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Abstract

Background

Plastics have been widely used for several decades, but their persistence in the environment has resulted in the widespread presence of microplastics (MPs) in the air, water, and soil. With particle sizes smaller than 5 mm, MPs are now recognized as emerging contaminants of concern owing to their potential impact on human health.

Objective

This study aimed to conduct a critical narrative umbrella review of published reviews and primary studies on microplastic exposure and human health. Specifically, the objective was to synthesize evidence across the major exposure pathways (ingestion, inhalation, and dermal), summarize the associated health outcomes, and critically appraise common themes, inconsistencies, and knowledge gaps. This review provides guidance for future research and policy directions by aligning findings with methodological strengths and limitations.

Results

MPs are consistently detected in food, water, air, human stool, blood, placenta, and breast milk. Reported outcomes include gastrointestinal inflammation, gut microbiota disruption, respiratory diseases, endocrine and reproductive dysfunction, and possible neurotoxicity. Inhalation is increasingly recognized as significant, and ingestion remains the most studied, whereas dermal exposure is underexplored.

Conclusion

Microplastics represent a pervasive and complex public health challenge. This umbrella review underscores the need for harmonized methodologies, epidemiological investigations, and mechanistic studies that reflect real-world exposure. Strengthening this evidence base is essential for risk assessment, regulation, and public awareness of the health impacts of microplastics.

Keywords

microplastic environment biodegradation health impact

Introduction

Over 320 million tons of plastics are produced each year, and their usage is currently widespread across society. Nevertheless, the long-lasting and enduring nature of plastic materials has led to notable ecological issues such as plastic waste buildup in landfill sites, streams, and oceans. Every year, almost 8 million tons of plastic debris are released into the ocean. Upon exposure to aquatic environments, plastics may deteriorate because of mechanical stress, microbiological activity, and radiation. The breakdown process results in the fragmentation of larger plastic items into tiny particles; plastic particles smaller than 5 mm are referred to as microplastics (MPs).¹ MPs are a particularly hazardous form of plastic pollution, posing significant risks to both the environment and human health.

Plastic particles smaller than 5 mm in diameter are termed MPs. MPs may come from various sources, such as the process of washing fabrics, which results in the release of microfibers,¹ and items for personal care that include microbeads.² As larger plastic particles break down in the environment, they gradually fragment into smaller pieces, contributing to the formation of MPs. This process is known as a partial decomposition.³ The widespread use of plastic products has led to the presence of MPs in several environmental media including water,⁴ soil,⁴ and air.² Research has shown that MPs are present in human feces,⁵ saliva,⁶ and placenta.⁷ This discovery has raised concerns regarding the possibility of bioaccumulation and the possible negative impacts on human health. Although the precise processes by which MPs influence human health are still under investigation, evidence points to contact with cutaneous tissue, inhalation, and ingestion as a means of entry.

MPs are present in seafood, water, and beer, making their ingestion a typical route of exposure.⁵ Skin contact with MPs may occur when coming into contact with polluted surfaces or when using personal care items,⁸ whereas inhalation of MPs via the air is possible, especially in indoor areas with high levels of dust.⁶ Although researchers are yet to completely comprehend the specific impact of MPs on the human body, their findings suggest that these small fragments pose several risks. These effects include tissue injury, inflammation, and oxidative stress.⁹ There have been findings indicating a correlation between exposure to MPs and adverse effects on male fertility and sperm quality. This might hinder successful conception and pose a hazard to reproduction.¹⁰ Several researchers have reported that MPs may accumulate in the human body gradually and have prolonged adverse health consequences in the long run.¹¹ MPs may induce bodily inflammation, which can subsequently result in many health complications including heart disease,¹⁰ cancer,¹² and autoimmune diseases.¹³ In addition, MPs can induce oxidative stress, which may harm cells and DNA. This may result in many health complications such as cancer, neurological disorders, and issues related to reproduction.¹⁴ The health impacts are usually worsened by chemical additives, including polychlorinated biphenyls and phthalate esters, which are incorporated into MPs during the manufacturing process. MPs are acknowledged as developing environmental and public health issues that can affect both human welfare and the natural environment. Many countries worldwide have issued regulations and banned the use of MPs in consumer products (Table 1).

Table 1.

Status of Regulating or Prohibiting the Use of Microbeads and Microplastics on Both the International and Domestic Levels.¹⁵

Year	Country	Legislation	Scope
2014	USA (Illinois)	Illinois Microbead Ban Act, Public Act 098-0342	Banned manufacture and sale of personal care products containing microbeads
2014	USA (New York)	Environmental Conservation Law, Section XYZ, S3932	Banned microbeads in cosmetic products
2014	USA (California)	California Senate Bill 1124 (SB1124)	Banned microbeads in rinse-off cosmetic products
2015	USA (Federal)	Microbead-Free Waters Act of 2015, Public Law 114-114	Phased nationwide ban on manufacture and sale of rinse-off cosmetics containing plastic microbeads
2016	Canada	Microbeads in Toiletries Regulations, SOR/2016-188	Prohibited manufacture, import, and sale of toiletries containing microbeads
2018-2021	New Zealand	Waste Minimisation (Microbeads) Regulations 2017, Section 23 of Waste Minimisation Act 2008	Banned sale and manufacture of personal care products containing microbeads
2019	Sweden	Ordinance (1998:944) on Prohibition in Certain Cases in Connection with Handling, Import and Export of Chemical Products	Amended to ban cosmetic products containing plastic microbeads
2020	Taiwan	Toxic and Concerned Chemical Substances Control Act – Amendment on Prohibited Ingredients in Cosmetic Products	Restricted use of microbeads in cosmetics and household chemicals
2019-2020	South Korea	Consumer Chemical Products and Biocides Safety Act (K-BPR) & Chemical Substances Safety Act (Partial Revision, 2025)	Developed test methods to detect microbeads in cosmetics; restricted microbeads in household chemicals

As the study of the health effects of MPs progresses, it is crucial to consistently identify the origins of these small fragments and to emphasize their potential consequences for human health. This study aimed to examine and clarify the complex relationship between MPs and human health with a focus on understanding the potential risks posed by these widespread contaminants. The sources of MPs, their entrance into the body, and the ways in which they interact with the human body were thoroughly investigated in this study. Furthermore, this study explored the routes (ingestion, inhalation, and skin contact) by which MPs enter the human body. As a result, the potential adverse health consequences related to MP infiltration are thoroughly understood.

Characteristics and Classification of MPs

The features and shapes of MPs can differ based on their origin and the environments in which they are found. These variations are summarized in Table 2. Generally, MPs range in size from a few millimeters (mm) to micrometers (μm) (16). Microplastic pellets, which are typically uniform in size, usually have a diameter of approximately 1 to a few millimeters. In contrast, microplastic fibers are often longer and thinner, with lengths ranging from approximately 10 μm to a few millimeters. Their sizes may vary greatly, ranging from a few micrometers to less than 1 μm (17).

Table 2.

Physical Properties of Different Categories of MPs.^16-18

Category of MPs	Physical Properties
Fragment	Irregular shape, sharp edges, thick, and often charred
Granule	Generally round in shape
Filament	Short, very small, and sometimes elongated
Pellet	Rounded overall appearance and predominantly flat on 1 side
Film	Thin and flexible
Foam	Soft texture, color (yellow to white)
Fiber	Circular form, with a length that is much longer than the breadth, thin and flexible

Primary MPs

Primary MPs are tiny plastic particles that are either intentionally manufactured in microscopic sizes or generated as byproducts of various industrial processes (Figure 1). These MPs are designed for specific purposes, such as their use as powdery materials in abrasive particles, injection molding, or resin pellets, which facilitate the transportation of polymers between various production sites. They may also result from progressive wear and tear of larger plastic products during use, production, or maintenance, such as synthetic textile erosion during washing or tire deterioration during driving.¹⁹

Figure 1.

Sources of microplastics.

Resin pellets, microbeads, and microfibers are some of the many shapes that these particles can take throughout their existence. Microbeads are small plastic spheres often used in personal hygiene and cosmetic goods. Some examples of these items are toothpaste and exfoliating scrubs.²⁰ Their primary function is to enhance the texture or act as abrasives. However, owing to their small size, microbeads can easily infiltrate water systems, making them difficult to remove using conventional wastewater treatment processes.²¹

Conversely, microfibers are fine plastic threads made from textiles such as synthetic clothes, carpets, and furniture. The apparel and fashion industries produce nearly 70 million tons of fiber annually, and a significant portion of the microfiber contamination in waterways comes from laundering these textiles. Microfibers are released at various stages of the textile life cycle, including manufacturing, usage, washing, and even disposal.²² Other sources including carpeting, personal care products such as wet cleansing wipes and facial masks, and tobacco filters have also been identified.²³

Resin pellets, often called nibs or nurdles, are the primary raw materials used for manufacturing plastic products. Incorrect handling or inadvertent spills during manufacturing, shipping, or processing may result in their release into the environment, which poses a severe danger to aquatic ecosystems. However, these substances have the potential to be discharged into the environment.^24,25

Secondary MPs

Secondary MPs are tiny plastic particles that are formed when larger plastic products break down. These large plastic products include containers, bags, and packaging supplies (Figure 1). Unlike primary MPs, which are produced at smaller sizes, secondary MPs are formed as larger plastic items break down over time, owing to different environmental factors.²⁶ Mechanical stresses, such as those caused by chemical reactions, friction, and waves, as well as exposure to sunlight, play a role in the deterioration of plastic items. These forces gradually decompose plastics into increasingly smaller pieces, eventually forming secondary MPs.²⁷

Most environmental MPs are believed to be secondary, primarily because macro plastics are frequently released into the environment. These secondary MPs may manifest themselves in a variety of ways, such as fragments, fibers, and even very small beads. Plastic fragments are bits of plastic that have fragments of erratic form and are the consequence of the disintegration of larger plastic products. The term “fiber” refers to the tiny strands that are generated from textiles such as fishing nets, ropes, and clothes. Microbeads are tiny cylindrical fragments that are similar in structure to primary MPs. Secondary MPs have the potential to damage ecosystems if released into their natural surroundings. These habitats include rivers, lakes, soil, and the air. The existence of these organisms may be dispersed over wide territories via their ability to be moved by water currents, wind, or human activity.²⁸

Tertiary MPs

Beyond the well-recognized categories of primary and secondary microplastics, recent literature has proposed the concept of tertiary microplastics. These particles undergo significant physical, chemical, and biological transformations after prolonged environmental exposure. Unlike secondary MPs, which are formed mainly through the fragmentation of larger plastics, tertiary MPs are characterized by extensive weathering, oxidation, sorption of environmental pollutants, and colonization by microbial biofilms.²⁷ These processes alter their surface chemistry, morphology, and toxicological profile, potentially rendering them more hazardous to human and ecological health. Tertiary MPs often act as vectors for persistent organic pollutants, heavy metals, and pathogenic microorganisms, thereby amplifying their ability to induce oxidative stress, inflammation, and endocrine disruption upon human exposure.¹⁷ Although the recognition of tertiary MPs remains relatively recent, it highlights the dynamic life cycle of plastic particles in the environment and underscores the importance of studying their complex interactions with living systems.²²

Routes of Exposure

MPs are prevalent pollutants that can enter the body via 3 main routes: ingestion, inhalation, and skin contact. These particles, found in various materials, fabrics, and dust, pose potential health risks via each of these exposure pathways.

Ingestion

Ingestion is the primary means by which humans are exposed to MPs. According to Borriello et al,²⁹ individuals consume approximately 39,000-52,000 fragments of MPs per year through food intake. These particles enter the gastrointestinal system either by consuming contaminated food or by being cleared from the respiratory system through the mucociliary process. This has the potential to cause an inflammatory response, heightened permeation, and alterations in the chemical composition and metabolism of gut microorganisms.

MPs have been found in several foods, including mussels,³⁰ commercially available fish,³¹ table salt,³² sugar,³³ and bottled water, indicating a high likelihood of human consumption. For example, Europeans are exposed to 11,000 MPs per capita annually through the ingestion of bivalves.³⁴ Furthermore, studies have estimated that individuals in Europe and China consume between 37 and 100 MPs per person per year via table salt.³⁵ Udovicki et al³¹ suggested that the deposition of MPs on tableware during meals may have a greater impact on human exposure than MPs already present in food. Dey et al³⁶ also emphasized that concerns over the pollution of ingested organisms may be excessive compared with the likely pollution caused by plastic containers and packaging.

Microplastic particles can be absorbed in the gut via specialized M-cells situated in Peyer’s patches, which are a particular region of the intestine. This occurs when particles are swallowed. The absorption rate may be influenced by how well the particles adhere to the mucus lining of the gastrointestinal tract, with higher adhesion leading to faster clearance.³⁷ Undissolved particles can enter the intestinal mucus by becoming more soluble through the adsorption of “corona” from the gut contents or owing to their small size. Experiments with polystyrene (PS) latex particles measuring 14 and 415 nm in rat digestive sections showed this ability, whereas larger particles (1.09 mm) did not exhibit the same capacity.³⁸

Persorption, another potential method of particle absorption, involves the transport of particles through a single layer of gastrointestinal epithelium via the paracellular route. MPs may undergo similar processes, as their movement to the circulatory system has been observed in living organisms after oral intake. For instance, Kik et al³⁹ reported that within 15 min of oral administration in rats, 6% of PS particles (0.87 mm) entered the bloodstream. Another study by Wu et al⁴⁰ showed that rats exposed to 50 nm PS particles at a dose of 1.25 mg/kg exhibited 34% absorption, with the particles likely carried through the mesenteric lymph to enter the circulatory system and accumulate primarily in the liver.

Additionally, human colon fibroblasts have been shown to internalize and release 44 nm PS nanospheres through passive transport across cell membranes, as demonstrated by Liu et al.⁴¹ When taken up by human gastric cancer cells, these 44 nm PS particles influence gene expression, reduce cell viability, and trigger structural alterations and pro-inflammatory reactions. Owing to food and environmental pollution, it is highly probable that humans are exposed to MPs through ingestion. However, the extent of the potential harm caused by consuming MPs remains uncertain because of the limited research assessing total human exposure and its impacts.

Inhalation

Multiple sources are responsible for the emission of MPs into the environment, including synthetic fabrics, wear and tear of materials such as automobile tires and structures, and re-suspension of MPs from different media. The first assessment of MPs in the air revealed that outdoor concentrations range from 0.3 to 1.5 particles per cubic meter, while indoor concentrations vary from 0.4 to 56.5 particles per cubic meter. These measurements included fragments of inhalable dimensions, accounting for 33% of the polymers.⁴² The estimated daily intake of airborne MPs through inhalation is 26-130 particles per day.⁴³

According to Bhat et al,⁴⁴ air samples taken using a mannequin showed that a male individual engaging in mild exercise was likely to inhale approximately 272 MPs daily. Various estimates depend on the sampling methodology and characteristics of the space, including cleaning schedules, activities, furnishing materials, and seasons. Lower density and smaller pieces penetrate deeper into the lungs owing to their particle shape and density. Following deposition, these particles may be cleared by macrophages or transported to the bloodstream or lymph nodes, resulting in their translocation.⁴⁵

Sharma et al⁴⁶ found that polyvinyl chloride (PVC) with a thickness of 2 mm, created using emulsion polymerization, caused significant toxicity in the lung cells of rats and humans, as well as the destruction of red blood cells (hemolysis). Airborne MPs in the workplace, such as flock, artificial fabric, and vinyl or polyvinyl chloride manufacturing, can lead to respiratory problems and interstitial lung disorders. Human pulmonary biopsies have shown the presence of 250 mm fibers, particularly in cancer biopsies, despite no proven causal link.⁴⁷ Thus, it is probable that pulmonary lesions may occur when exposed to larger amounts of airborne MPs or when individuals are more susceptible.

Dermal Contact

Nanoplastics (less than 100 nm) can cross the epidermal barrier; however, skin contact with MPs is typically regarded as less harmful.⁴⁸ Household appliances are a frequent source of exposure to plastic monomers and additives, including endocrine disruptors, such as bisphenol A and phthalates, via skin contact. However, in the absence of concrete evidence, it is inappropriate to dismiss the potential of nanoplastics to penetrate the dermal barrier and induce.⁴⁹

Medical professionals are aware that when plastics are encased in fibrous tissues, they may cause a foreign body response and mild inflammation. A study by Chang et al⁵⁰ found that surgical sutures made of braided polyester and monofilament polypropylene caused less inflammation after 3 weeks compared to those made of silk and fibrous encasing. Additionally, a study conducted by Hu and Palic (10) highlighted that both micro- and nanoplastics can cause inflammation and immune system responses. The differences in the surface properties between the 2 may lead to varying effects. Additionally, microplastics and nanoplastics can trigger oxidative stress in human epithelial cells.⁵¹ Given the extensive skin exposure to plastic fragments, such as pollen, synthetic yarn, and microbeads in beauty products, the potential negative consequences of nanoplastics require further study in this field.

Absorption, Distribution, Metabolism, and Excretion (ADME) Profile of MPs

Vattanasit et al⁵² found that inhaled MPs could penetrate the respiratory epithelium and be absorbed into the bloodstream. Similarly, Fournier et al⁵³ reported that ingested MPs can pass through the gastrointestinal tract and enter the systemic circulation, potentially reaching various organs. The uptake of MPs in the gut is influenced by particle size, shape, surface charge, concentration, and chemical composition. The intestinal mucus layer acts as the first barrier, with an effective mesh size reported in the 10-200 nm range, meaning that larger MPs in the micrometer range are generally retained and cleared in the lumen, whereas smaller sub-micrometer and nanoplastic fractions can penetrate the mucus and reach the epithelium. Surface chemistry also plays a role; hydrophobic or charged surfaces tend to adhere to mucus, whereas neutrally coated particles may diffuse more readily.

The size and surface characteristics of the MPs significantly influence their absorption. Smaller MPs, particularly those in the nano-size range, have a greater ability to cross biological barriers. Banerjee and Shelver⁵⁴ showed that nano-sized MPs (less than 100 nm) were more likely to penetrate cell membranes and enter systemic circulation compared to larger particles. However, MPs between 100 nm and ∼1 μm may also cross the mucus barrier under certain conditions, although at a much lower efficiency, particle aggregation can increase retention in mucus. This enhanced absorption potential raises concerns regarding the health risks associated with MP exposure.

For inhalation exposure, the deposition patterns depended on aerodynamic diameter. Particles >10 μm tend to deposit in the nasal passages and upper airways, those between 2.5 and 10 μm in the tracheobronchial tree, and particles <2.5 μm, especially ultrafine particles <0.1 μm, can reach the alveoli, where they may cross the alveolar-capillary barrier. The shape, density, and surface chemistry further influence deposition and clearance by mucociliary transport or macrophage uptake. Fibrous MPs, for example, may resist clearance and persist longer in lung tissues.

Once absorbed, MPs are distributed throughout the body via the blood stream. Studies have identified MPs in various tissues and organs such as the lungs, liver, and kidneys. Schwabl et al⁵⁵ detected MPs in human liver and lung tissues, indicating widespread distribution. Yong et al⁵⁶ also observed MP accumulation in the livers and spleens of animal models, suggesting that MPs can reach and persist in these organs.

Unlike organic compounds, MPs are resistant to metabolic processes. They are not easily broken down by metabolic enzymes, which contributes to their persistence in the body. Prata et al⁵⁷ noted that MPs remain relatively unchanged after absorption, leading to their accumulation in tissues and prolonged exposure. Polymer types (such as PE, PS, and PET) and the presence of additives or adsorbed pollutants can also affect bio-persistence and potential toxicity. The interaction of MPs with biological molecules (lipids and proteins) can influence their behavior within the body. Sun et al⁵⁸ found that MPs could bind to proteins in the bloodstream, affecting their distribution and interaction with cells. However, the lack of significant metabolic degradation poses a challenge for understanding the full extent of MP impact.

MPs are primarily excreted through feces and urine. Ramsperger et al⁴⁸ reported that MPs ingested through contaminated food or water are typically excreted in feces, while inhaled MPs may be cleared through mucociliary action and expectoration. Nonetheless, particle size and shape strongly influence retention; larger or fibrous particles tend to be trapped in mucus and eliminated, whereas smaller particles that cross epithelial barriers may evade excretion and accumulate in tissues, leading to potential long-term exposure.

Health Impacts of MPs

Although research on the health impacts of MPs is still ongoing, there is evidence that exposure to these microscopic plastic particles may have adverse effects on human health. This section examines the many documented health effects linked to the consumption of MPs, categorized based on their mode of ingestion. Figure 2 and Table 3 illustrates the impact of human exposure to MPs on human health.

Figure 2.

Health impact of microplastics.

Table 3.

Organ-specific Health Impacts of MPs.

System Affected	Potential Diseases/Conditions	Key Observations	References
Skin	• Allergic reactions	Research mostly limited to allergic responses; a few human studies available	(^5,11,76)
Skin	• Contact dermatitis		(^5,11,76)
Gastrointestinal tract	• Inflammatory bowel disease (IBD)	Positive correlation between IBD severity and fecal MPs; minimal human research on microbiota impacts	(^53,119,120)
	Colorectal and pancreatic cancer
	Gut barrier dysfunction
	Metabolic disorders
	• Non-alcoholic fatty liver disease
Respiratory system	• Occupational hypersensitivity pneumonitis	Primarily studied in occupational settings; some diseases linked to exposure to specific plastics like polyacrylic nanoparticles and styrene	(^24,43,62)
	• Lung cancer
	• Obstructive bronchiolitis
	• Respiratory issues (coughing, dyspnea, wheezing)
	• Pleural effusion
Blood and hematologic system	• Leukemia	Associations found primarily in occupational settings with long-term exposure	(^6,107,121)
	Bladder cancer
	Lymphohematopoietic neoplasms
Nervous system	• Neurotoxic effects (headache, fatigue, dizziness	Correlation found with environmental styrene exposure; more research needed to confirm causation	(^5,30,122)
	• Encephalopathy
	• Unspecified dementia
	• Degenerative neurological disorders
Musculoskeletal system	• Periprosthetic osteolysis	Linked to polyethylene (PE) particles in hip prostheses	(^38,122,123)
Reproductive system	• Decreased fertility	Effects observed mainly in animal studies; human impact not thoroughly studied	(^4,15,49,103)
	• Gonadal damage
	Reduced offspring weight
Genetic material	• DNA damage	Evidence from occupational exposure to styrene; potential link to specific genotypes	(^{12,15,124,125})
Genetic material	Increased sister chromatid exchange frequency		(^{12,15,124,125})

Ingestion

Microplastic ingestion has been associated with several health effects such as gastrointestinal problems, alteration of the endocrine system, and toxicity.

Gastrointestinal Problems

Microplastic exposure has been identified as a substantial health hazard associated with gastrointestinal symptoms. Studies have indicated that consuming microplastic particles, whether from contaminated food or water, may result in a range of gastrointestinal problems. These include bloating, digestive system inflammatory conditions, irritable bowel disorder, alterations in intestinal permeability, and gut bacterial imbalance.^31,59 Furthermore, it has been shown that MPs accumulate in the digestive tract, potentially causing physical discomfort and obstructions. The biological effects of MPs on the gastrointestinal system are expected to arise from their adjuvant activity, which may amplify the immune response to biomolecules attached to their surface. This interaction can lead to significant health consequences.^37,59 Exposure to microplastics may disrupt the symbiotic relationship between the host and naturally occurring gut microbiota, resulting in a condition known as dysbiosis, which refers to an imbalance in the microbial communities of the gut. It can negatively affect digestion, immunity, and overall gut health. The presence of microplastics could therefore exacerbate these imbalances, potentially leading to a range of gastrointestinal issues and broader health problems.⁶⁰ MPs in zebrafish have detrimental consequences in the intestines, including mucosal injury, inflammation, increased permeability, and disruption of metabolic processes.⁶¹

Elevated levels of MPs result in modifications to the gut microbiota, heightened inflammation, and modifications to immune cell populations.⁶² Recent studies have also examined the impact of human consumption of MPs. Visalli et al⁶³ investigated the effects of microplastics of different sizes (3 and 10 μm) on human intestinal cells. The results revealed that a moderate degree of cytotoxicity was caused by both the particle sizes. However, smaller particles had a more noticeable effect on the cell membranes. Kaseke et al⁶⁴ conducted recent research that discovered the first occurrence of polymer breakdown in human digestion. These results indicate that MPs have the potential to damage the digestive system. Individuals with inflammatory bowel disease have been found to have higher levels of microplastics in their stools than healthy individuals. This suggests a potential link between microplastics and the development or progression of inflammatory bowel disease.

Endocrine Disruption

MPs are acknowledged as having the potential to cause endocrine disruption. They can adsorb and retain various substances from their surroundings, including endocrine-disrupting compounds (EDCs). EDCs are external substances or mixtures that can interfere with the normal functioning of the endocrine system, potentially leading to adverse health effects in organisms.^65,66 When microplastics are ingested or come into contact with living organisms, they can release EDCs, which may disrupt endocrine function. This disturbance may have negative consequences for hormonal equilibrium, reproductive capacity, growth, and general well-being.⁶⁷ The presence of EDCs was more probable because of the minute dimensions and extensive dispersion of MPs.

Leso et al⁶⁸ examined the effects of polystyrene MPs (PSMPs) on the availability of microcystin-LR (MCLR) and its impact on the reproductive system of zebrafish. PSMPs increased the accumulation of MC-LR in the reproductive organs of zebrafish and exacerbated the harmful effects of MC-LR on the reproductive system. PSMPs also affect sex hormone levels and disrupt the hypothalamic-pituitary-gonadal axis, aggravating reproductive failures.⁶⁹ All examined Atlantic horse mackerel samples from the Middle Mediterranean Sea were confirmed to have MPs in their gastrointestinal system. Vitellogenin, a biomarker suggesting disturbance of the endocrine system, was found in the livers of male specimens, indicating that the fish species had widely consumed plastics.⁷⁰ Japanese medaka fish experienced changes in gene expression and aberrant proliferation of germ cells as a result of exposure to MPs and the chemicals they contain.⁷¹ These findings suggest that adult fish may have endocrine system problems when there is a lot of plastic trash in their surroundings.⁷² Although evidence suggests that MP additive compounds may have adverse consequences, our knowledge of how these chemicals leak from different types of polymers and their potential influence on human health is still limited.⁷³

MPs as Vectors for Pathogens and Antibiotic-Resistant Bacteria

MPs quickly attract bacteria and a wide variety of species, similar to other surfaces observed in marine settings, leading to the development of intricate biofilms. Stabnikova et al⁷⁴ used the term “plastisphere” to refer to the distinct microbial communities that live on the surfaces of MPs in marine settings. Plastic surfaces that are exposed to saltwater have been shown to swiftly produce a protective layer and succeeding biofilm, both of which have a different structure than the surrounding seawater that is around them. When serving as vectors for dangerous bacteria, MPs can pollute water supplies and food chains, thereby facilitating the transmission of illnesses.⁷⁵ After consumption, MPs and the accompanying pathogenic bacteria may accumulate in the digestive system, which may lead to inflammatory reactions or infections. Certain pathogenic bacteria discovered on MPs have been associated with respiratory infections, gastrointestinal ailments, and skin problems in humans.⁷⁶

Research conducted in Hong Kong’s wastewater treatment facilities has investigated the colonization of sewage by MPs. A study found that bacterial populations formed biofilms on the surfaces of polyethylene microbeads that had been incubated in untreated sewage.⁷⁷ The research showed a progressive rise in the variety of bacteria over time and detected the presence of bacteria that may cause diseases in humans and fish on MPs. This suggests that MPs can carry pathogenic microorganisms in sewage. Fleischmann et al⁷⁸ effectively detected the presence of Vibrio parahaemolyticus on several kinds of MPs obtained from the North and Baltic Sea. This finding suggests that the colonization of MPs by Vibrio may have originated from surrounding seawater. These results highlight the significance of investigating the spread and endurance of these harmful bacteria on MPs in the ocean, especially in terms of possible health hazards linked to microbial communities connected with MPs.⁷⁸ A similar study detected the presence of Escherichia coli and Vibrio spp. on plastic resin pellets collected from public swimming beaches.⁷⁹

Moreover, there is increasing concern about the existence of antibiotic-resistant microorganisms in MPs. The transfer of resistance genes from these bacteria to other bacteria facilitates the dissemination of antibiotic resistance, leading to substantial difficulties in health care and the management of bacterial illnesses. A study discovered that MPs present in mariculture systems include antibiotic-resistant bacteria (ARB) and multi-antibiotic-resistant bacteria.⁸⁰ MPs have shown resilience to many antibiotics including penicillin, sulfafurazole, erythromycin, and tetracycline.⁸¹ MPs can serve as carriers of antibiotic-resistant bacteria. Silva et al⁸² have shown that MPs can harbor and transport bacteria, including those with antibiotic-resistant genes, facilitating their spread across different environments. MPs support the formation of bacterial biofilms. Nguyen et al⁸³ found that antibiotic-resistant bacteria can form biofilms on MPs, which can be more resistant to antibiotic treatment compared to planktonic bacteria. Biofilm formation on MPs can enhance the survival and persistence of drug-resistant strains. The presence of MPs in aquatic environments can affect microbial communities and potentially contribute to the spread of antibiotic resistance. Furthermore, there is increasing concern regarding the long-lasting presence of detrimental compounds such as pesticides and polycyclic aromatic hydrocarbons, which stick to plastics and serve as vehicles for these harmful pollutants.

MPs in Human Biological Samples

Recent studies have reported the presence of MPs in the human blood, indicating systemic exposure and the potential for MPs to circulate throughout the body. For example, Yang et al⁸⁴ detected MPs in blood samples from individuals across different regions, underscoring the widespread nature of this contamination. The implications of MPs in the blood are significant, as they may lead to internal exposure and interaction with various organs and systems. MPs have also been identified in the saliva and urine, suggesting both ingestion and excretion pathways. Abbasi et al⁸⁵ found MPs in the saliva of individuals who consumed contaminated water, whereas Pironti et al⁸⁶ reported the presence of MPs in urine samples, highlighting the body’s attempt to eliminate these particles. The detection of MPs in the placenta, as reported by Zurub et al,¹⁴ raises concerns regarding fetal exposure. The ability of MPs to cross the placental barrier suggests potential risks to fetal development and long-term health consequences for the offspring. MPs have been found in various tissues and bone marrow, indicating their possible accumulation and adverse effects on cellular functions. A study by Yong et al⁵⁶ documented MPs in lung and liver tissues, linking their presence to inflammation and potential toxicity. Bone marrow contamination, as noted by Jing et al,⁸⁷ may affect hematopoiesis and overall immune function. The presence of MPs in breast milk, as reported by Caba-Flores et al,⁸⁸ highlights concerns about infant exposure during breastfeeding. Given the critical role of breast milk in early development, MPs may pose a risk to infant health and development. MPs have been detected in stool and sputum samples, reflecting the excretion of ingested or inhaled particles. Huang et al⁸⁹ and Schwabl et al⁵⁵ found MPs in these samples, providing insights into the body’s elimination processes and potential environmental sources of contamination.

MPs Crossing Blood-Brain Barrier

Yang et al⁹⁰ demonstrated that MPs can be detected in the brain tissue after systemic exposure. Their study found that inhaled or ingested MPs could potentially enter the central nervous system (CNS) and accumulate in brain regions, raising concerns about possible neurological impacts. Kopatz et al⁹¹ explored the mechanisms by which MPs can cross the BBB. They reported that MPs smaller than 100 nm were more likely to penetrate the BBB because of their size and surface properties. This study highlighted that MPs might disrupt tight junctions between endothelial cells, facilitating their entry into the CNS. Jin et al⁹² investigated the neurotoxic effects of MPs in animal models. They found that exposure to MPs leads to neuroinflammation and oxidative stress in the brain, suggesting that the ability of MPs to cross the BBB contributes to neurological damage and cognitive impairment.

Impact of MPs on Reproductive Health

Studies by Ribas-Maynou et al⁹³ and Xie et al⁹⁴ have found that MPs can impair sperm quality by inducing oxidative stress and inflammation. This can lead to reduced sperm motility, concentration, and viability, potentially affecting the fertility. MPs have been found in the placenta, suggesting that they can cross the placental barrier. Chen et al⁹⁵ demonstrated that MPs could accumulate in the placenta, potentially affecting fetal development and health.⁹⁶ Once MPs cross the placenta, they can expose the fetus to potential risks. Zurub et al¹⁴ found that fetal exposure to MPs can lead to developmental issues and an increased risk of health problems later in life.

Inhalation

Inhalational exposure to MPs is associated with several health issues, including respiratory and cardiovascular issues.

Respiratory Problems

Respiratory health may be adversely affected by inhalation of MPs present in air. These minuscule particles may provoke inflammation and irritation in the respiratory system, resulting in symptoms such as wheezing, coughing, difficulty in breathing, and worsening of established respiratory disorders such as asthma.⁷⁶ The size of the fiber affects its toxicity. While larger fibers are more lasting and damaging to lung cells, thinner fibers may be inhaled into the respiratory system. The lungs cannot efficiently remove fibers with a size range of 15-20 μm.⁹⁷ Fibers longer than 10 μm and smaller than 0.3 μm are considered the most hazardous.⁹⁸ The health consequences of microplastic are especially worrisome for individuals employed in the synthetic textile and flock industries.⁹⁹ Previous research that has examined the lung tissue of workers in the textile industry has shown that synthetic fibers are present, leading to respiratory distress.¹⁰⁰

A study examining the lungs of workers exposed to nylon flocks found that some individuals had a chronic lung illness called interstitial lung disease, even after leaving the workplace. This condition causes gradual deterioration in lung function, culminating in secondary pulmonary hypertension and respiratory failure.¹⁰¹ This underscores the necessity of conducting medical monitoring and taking steps to limit exposure in the polypropylene flock business by implementing these methods.¹⁰² Furthermore, airborne fibrous MPs have a water-repellent surface that allows them to soak contaminants from their surroundings.¹⁰³ Within urban environments, MPs coexist with vehicle pollution and can carry polycyclic aromatic hydrocarbons (PAHs) and hazardous metals. Upon emission, they may have harmful consequences on lung health such as genotoxicity.¹⁰⁴ The breakdown of PAHs linked to fibrous MPs might result in both stable and unstable DNA damage, which can contribute to possible harmful consequences.^104,105 Prolonged exposure to airborne MPs can contribute to chronic respiratory conditions such as chronic bronchitis and chronic obstructive pulmonary disease. Akhbarizadeh et al²⁰ have highlighted the association between exposure to industrial dust and respiratory illnesses in those working in the plastic and rubber industries.

Cardiovascular Problems

These tiny particles have been reported to cause oxidative stress and inflammation, affect the function of the inner lining of blood vessels, and disrupt normal heart function, thereby increasing the risk of cardiovascular issues.⁷⁶ Moreover, the capacity of MPs to gather noxious chemicals from their surroundings introduces an additional level of apprehension, since these compounds may potentially have adverse effects on the cardiovascular system. Most animal models have been used to study the role of MPs in the development of cardiovascular diseases. Studies have shown that higher concentrations of MPs lead to decreased viability of mammalian cells, increased cell metabolism, and changes in genes related to inflammation and oxidative stress.¹⁰⁶

A number of studies have shown that increasing the quantity of MPs administered to mice results in changes to the hematological systems, gene regulation, and pathways related to immune system activity and metabolism in bone marrow cells.¹⁰⁷ Li et al¹⁰⁸ investigated the effects of PS MPs on the cardiovascular system. These findings demonstrate that PS MPs induce elevated levels of collagen synthesis, heart damage, oxidative stress, and activation of the fibrosis-related Wnt/β-catenin pathway. These findings suggest that PS MPs may harm the cardiovascular system by stimulating scar tissue formation in the heart and initiating injury to the heart muscle via oxidative stress. Huang et al¹⁰⁹ discovered that mice that ingested PS MPs exhibited higher fat mass, weight gain, increased insulin levels, and developed insulin resistance. The correlation with obesity was further reinforced by analyzing gene expression and gut microbiota.

Recent research has also shown a clear correlation between MPs and cardiovascular disease. Exposure of liver cells and human kidneys to PS MPs resulted in altered gene expression of important enzymes, reduced cell growth, defects in structure, and increased amounts of ROS.¹¹⁰ Wu et al¹¹¹ studied whether foreign particles were present in blood clots collected from patients who had heart surgeries. The thrombi included a variety of particles, including synthetic components, which were discovered during the examination. These results highlight the underestimated adverse health effects associated with exposure to microparticles and underline the need for further studies in this area. The effects of PSMPs on human vascular endothelial cells were also investigated by Chen et al.¹¹² PSMPs have been shown to induce oxidative stress, impair vascular barrier function, and induce apoptosis. Nevertheless, when individuals were subjected to PSMPs at blood concentrations that mimicked real-life conditions, there was no substantial increase in the likelihood of developing atherosclerosis. This implies that exposure to PSMPs is associated with a low cardiovascular risk.

Dermal Contact

The possibility of skin irritation and allergic responses cannot be excluded, even if there are no definitive data showing that MPs are harmful when they come into direct contact with the skin.

Skin Irritation

MP particles can induce skin irritation, itching, redness, and inflammation upon contact. The rough texture of some MPs and their ability to block pores or disturb the natural protective functions of the skin might lead to these negative responses. Additionally, MPs may include additives or pollutants that cause skin irritation.¹¹³ Contact between MPs and chemical additives in plastics can cause skin irritation, dermatitis, and allergic reactions. Research by Muhib et al¹¹⁴ indicated that workers with direct skin contact may develop rashes and other dermatological conditions. Extended or recurrent contact with MPs may cause persistent skin irritation and exacerbate pre-existing skin disorders. However, a toxicity investigation conducted in rats showed that prolonged exposure to PP MPs did not cause any irritation to the eyes or skin.¹¹⁵ However, the potential for this phenomenon must be disregarded.

Allergic Reaction

Exposure of the skin to microplastics may lead to the development of allergies and trigger immunological responses. When the body’s immune system detects foreign particles, they may be hazardous and produce histamines and other inflammatory compounds, which may cause allergy symptoms. The symptoms may include pruritus, erythema, edema, urticaria, and, in rare instances, more serious responses, such as anaphylaxis.¹¹⁶ Individuals with any form of allergy or sensitivity are more prone to developing allergic responses to MPs. Research has reported that when individuals are exposed to elevated levels of PP MPs, they might stimulate immunological reactions and heighten cellular hypersensitivity.¹¹⁷ Hwang et al¹¹⁸ found that while increased levels of PS particles did not induce histamine release or allergic responses in HMC-1 cells, they did cause inflammation in the early stages (Table 3).

Results and Discussion

Overview of the Literature

Our structured search identified a large body of reviews and primary studies addressing human exposure to MPs and their associated health outcomes. Since 2018, there has been an exponential increase in publications, with systematic and scoping reviews focusing on exposure pathways, toxicological mechanisms, and biomonitoring. In addition, a growing number of studies have reported MPs in human biological matrices, including stool, blood, placenta, breast milk, urine, and sputum. This confirms that exposure is not theoretical but measurable in humans. However, these studies often differ in scope, methodology, and sensitivity of detection, making direct comparison difficult.

Umbrella synthesis indicates that ingestion, inhalation, and dermal contact are the dominant routes of entry into the human body. Among these, ingestion has received the most research attention, with systematic reviews reporting estimated annual intakes ranging from 39,000 to 52,000 MP particles per individual. Inhalation has emerged as a significant pathway in indoor and occupational settings, with biopsy evidence supporting particle accumulation in the lungs. Dermal exposure remains the least characterized, although in vitro studies have suggested the potential of nanoplastics to penetrate the skin barrier. Together, these findings provide a compelling case for widespread exposure but raise urgent questions about the extent of associated health risks.

It is also evident that most toxicological and mechanistic studies rely on pristine laboratory-generated polystyrene particles. Although these models are valuable for mechanistic insights, they fail to capture the complexity of environmental MPs, which are often aged, chemically laden, and biologically colonized. This methodological gap creates uncertainty when extrapolating laboratory results to real-world human exposure. Hence, while the literature provides strong evidence for exposure and biological plausibility, its translation into clinical outcomes remains uncertain.

Results of the Review

Ingestion has consistently been reported as the primary route of human exposure. Microplastics have been detected in a wide variety of foods, including seafood, salt, sugar, bottled water, and beer. Several studies have confirmed the uptake of MPs into the gastrointestinal tract, with MPs detected in human stool samples. Experimental data support absorption through specialized intestinal cells, and subsequent systemic distribution has been observed in animal models. Clinical studies have also reported higher fecal MP loads in individuals with inflammatory bowel disease, suggesting a link between exposure to MPs and gastrointestinal pathology. However, the strength of the evidence remains variable, as most findings rely on cross-sectional or laboratory-based investigations.

Inhalation has been highlighted in multiple reviews as a significant, but underexplored pathway. The concentrations of airborne MPs vary greatly depending on the setting, with indoor levels generally being higher than outdoor levels. Occupational studies in the textile and plastic industries have linked exposure to respiratory diseases including interstitial lung disease and chronic inflammation. Autopsy and biopsy confirmed the presence of MPs in the lung tissue, reinforcing biological plausibility. However, methodological inconsistencies in sampling coupled with limited longitudinal data hinder definitive conclusions regarding causality and population-level risk.

Dermal exposure is rarely addressed in systematic reviews but appears in a handful of experimental and occupational studies. Although microplastics larger than 100 nm are unlikely to penetrate intact skin, nanoplastics demonstrate the ability to cross epithelial barriers in vitro. Workers handling plastics or those exposed to synthetic textiles have reported dermatitis and allergic reactions, although confounding factors make attribution difficult. Overall, dermal exposure remains the least understood pathway, and its contribution to the systemic burden is likely modest compared to ingestion and inhalation.

Common Themes

The pervasiveness of human exposure is a dominant theme in the literature. Through food, air, or direct contact, MPs are consistently found in multiple biological matrices, demonstrating their ability to enter and circulate in the human body. This ubiquity raises significant public health concerns even in the absence of definitive disease attribution. Another recurring theme is the biological plausibility of harm, which is supported by robust evidence from animal and cellular models. These studies consistently demonstrated inflammation, oxidative stress, immune dysregulation, endocrine disruption, and, in some cases, genotoxicity following MP exposure.

Despite this strong mechanistic foundation, the translation to human health outcomes remains weak. Epidemiological evidence is scarce, and most human studies are descriptive rather than causal. For example, MPs have been detected in the blood, placenta, and breast milk; however, the clinical consequences of these findings are uncertain. Likewise, associations with gastrointestinal and respiratory diseases are intriguing, but preliminary. The gap between mechanistic plausibility and clinical evidence represents a major challenge in this field.

Finally, methodological heterogeneity undermines the ability to compare results across studies. Variations in particle isolation, size thresholds, polymer identification techniques, and contamination control create inconsistencies that complicate the synthesis. Most toxicological studies rely on pristine particles, which likely underestimates the toxicity of environmentally weathered MPs. These recurring themes suggest that while exposure is well established, the true scale of its health impact remains unclear.

Gaps in Evidence

Several critical knowledge gaps have emerged from this umbrella review. First, there is a lack of standardized protocols for the detection and quantification of MPs in human tissues. The current methods vary widely, raising concerns regarding reproducibility and contamination. Without harmonized approaches, it is difficult to establish reliable prevalence or burden estimates.

The second gap lies in epidemiological research. The literature lacks large longitudinal cohort studies capable of linking MP exposure with specific health outcomes. Most evidence remains cross-sectional or is derived from high-exposure occupational settings. This limits our ability to assess chronic health risks or establish dose-response relationships.

The third gap is the near absence of data on nanoplastics, which are smaller, more biologically mobile, and potentially more harmful than microplastics. While in vitro studies have shown that nanoplastics can cross barriers such as the blood-brain and placental barriers, human evidence is nearly nonexistent. Similarly, little is known about the interactions between MPs and co-pollutants, including persistent organic pollutants, heavy metals, and microbial biofilms, all of which may exacerbate toxicity. Addressing these gaps is essential for advancing risk assessment and regulatory decision making.

Conclusion and Future Directions

The increasing use of plastics, coupled with their enduring characteristics, has increased the vulnerability of people to MPs. MPs might potentially produce inflammatory lesions when they come into contact with tissues, especially in cases of high concentrations or high individual vulnerability. The rising prevalence of neurological illnesses, immunological disorders, and malignancies may be attributed to increased exposure to environmental pollutants such as MPs. Even when using the precautionary principle, the considerable uncertainty that emerges from this lack of knowledge should not be alarming. Given the anticipated increase in the presence of these artificial substances in our surroundings, more research is necessary to comprehensively understand the potential harm of MPs to human well-being. This entails acquiring information on human exposure, pathophysiology, and resulting effects.

Future Directions

While there is currently no substantial evidence of a widespread threat to human health from microplastics, understanding the extent of human exposure, particularly to particles smaller than 10 μm, is crucial.¹¹⁵ Modeling studies on polystyrene microplastics suggest that safe exposure levels for humans range between 5.1 and 53.3 milligrams per gram of body weight.³⁷ This range represents the minimum exposure required to trigger the effects of the most sensitive biomarker. However, it is important to note that actual exposure levels are unlikely to reach these thresholds in typical scenarios.¹²⁶ Continued research and monitoring are essential to accurately assess and manage the potential risks associated with microplastic exposure.

This result is supported by several investigations that have examined the consumption of MPs in the context of environmental exposure to other additives and toxins that are often found in the environment. These studies emphasize the need for further research, owing to the existing dearth of evidence for risk assessment.¹²⁷ Moreover, plastics used in toxicological experiments often exhibit distinct surface characteristics, weathering, and adsorption of chemicals and organisms compared with their ambient equivalents, resulting in erroneous findings. Therefore, it is necessary to further investigate the potential risks of MPs to public health. This includes examining not only the concentrations of MPs that are present in the environment but also the specific features of these MPs that are significant to the environment. MPs enter the human body when inhaled, ingested, and come into contact with the skin, which may result in the development of chronic inflammatory lesions. Estimations can be used to evaluate human exposure to MPs including inhalation⁴⁸ and ingestion.¹²⁸

Human exposure may be determined more accurately by modifying standard diagnostic techniques.¹²⁹ Nevertheless, there is still a need for advanced techniques to detect plastics in these materials, including processes such as tissue digestion or histological section staining. These approaches are inherently constrained by the restricted availability of tissue and possibility of sample contamination, particularly because of the prevalent use of plastic materials in pharmaceutical products. The evaluation of the effects of MPs on human health may be aided by research conducted on model organisms, such as rodents or rats, or on cell cultures. Efforts to establish a connection between exposure and poor outcomes via observational studies may be undertaken; however, this will likely require the use of large sample sizes and meticulous attention to confounding factors.

Footnotes

Author Contributions

SM and RR contributed significantly to the original designing, drafting, and writing of the manuscript.

Declaration of Conflicting Interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Sandhya Jinesh

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Microplastics: A Narrative Review on Modes of Exposure and Impact on Human Health

Abstract

Background

Objective

Results

Conclusion

Keywords

Introduction

Characteristics and Classification of MPs

Primary MPs

Secondary MPs

Tertiary MPs

Routes of Exposure

Ingestion

Inhalation

Dermal Contact

Absorption, Distribution, Metabolism, and Excretion (ADME) Profile of MPs

Health Impacts of MPs

Ingestion

Gastrointestinal Problems

Endocrine Disruption

MPs as Vectors for Pathogens and Antibiotic-Resistant Bacteria

MPs in Human Biological Samples

MPs Crossing Blood-Brain Barrier

Impact of MPs on Reproductive Health

Inhalation

Respiratory Problems

Cardiovascular Problems

Dermal Contact

Skin Irritation

Allergic Reaction

Results and Discussion

Overview of the Literature

Results of the Review

Common Themes

Gaps in Evidence

Conclusion and Future Directions

Future Directions

Footnotes

Author Contributions

Declaration of Conflicting Interests

Funding

ORCID iD

References