Abstract
H.C. Red No. 1 is an aromatic compound used as a colorant in semipermanent hair dyes and colors. This ingredient is reportedly used in almost 50 products; one manufacturer reports current use concentrations of 0.5%. These products will generally have a warning statement and patch test instructions that should be followed to determine whether each individual user is sensitive to the product before use. In a study performed using human female cadaver skin, the percutaneous absorption of H.C. Red No. 1 was linear for the first 4 h, with total absorption of 1.68% after 48 h. The oral median lethal dose was between 2.5 and 5.0 g/kg for male rats and 0.625 and 1.25 g/kg for female rats. Short-term oral feeding of H.C. Red No. 1 to rats had effects on several organ weights and resulted in liver and splenic lesions. Dermal exposure to almost twice the oral concentration produced no evidence of toxicity. In rabbits, H.C. Red No. 1 was not a dermal irritant, but it was a mild ocular irritant. H.C. Red No. 1 was a contact sensitizer, but not a photosensitizer, in guinea pigs. No reproductive or developmental toxicity was observed when a formulation containing 0.15% H.C. Red No. 1 was applied dermally to rats, and neither fetotoxic nor teratogenic effects were seen in rats fed 0.1% H.C. Red No. 1. No evidence of mutagenic potential was seen in most bacterial and mammalian assays. No carcinogenic effects were reported for mice dosed dermally with H.C. Red No. 1, but several possible effects were seen in a rat skin-painting study with 0.15% H.C. Red No. 1, including liver enlargement, parathyroid and hepatocellular hyperplasia, hepatocellular hypertrophy, hyperkeratosis in several locations, and dermatitis. Whether these effects were compound-related was unclear. A repeated-insult patch test of a 3% slurry of H.C. Red No. 1 completed on 103 individuals with normal skin reported one possible and one definite sensitization reaction. Because the ingredient is used at a low concentration and very little is actually absorbed, the oral exposure data using concentrations of 0.1% represent a much higher exposure than would occur through the skin. The general absence of toxicity in such oral studies supports the safety of use of H.C. Red No. 1 in hair dye formulations at concentrations of 0.5%.