Abstract
Environmental factors in airplanes may precipitate headaches. We conducted a questionnaire-based study among consecutive travellers to determine the rate, severity and duration of flight-associated headaches (FAHA). Of the 906 eligible travellers (mean age 33.3 ± 13.8 years), 22.3% reported headaches at least once per month. FAHA occurred in 52 travellers (5.7%), of whom 34 were women (P = 0.0023 vs. none FAHA). The duration of pain was 4.0 ± 10.2 h after takeoff and continued for 5.7 ± 14.2 h after landing. Migraine was diagnosed in 19.2% of those with FAHA. The magnitude of headache was 6 ± 2 (on a scale of 1-10). Among those who suffer from FAHA, 45.4% reported that their pain was unilateral, in contrast to 72.7% among those with ‘non-flight’ headaches (P = 0.019). Nine travellers had headaches when descending to −400 m below sea level, and nine upon climbing to high altitude. This preliminary observation indicates that FAHA is not uncommon and should be further investigated.
Introduction
Headache is a common symptom. About 40% of the population will suffer severe, disabling headache at least once a year (1). The commonest types of headache are tension headaches and migraine. Numerous studies have shown a direct link between environmental or personal factors and headaches (2–4). One of the least investigated fields is that of flight-associated headache (FAHA) (5, 6).
There is a debate in the literature about the role of barometric pressure in the development of headaches. Although headaches constitute a common symptom in response to a fall in barometric pressure on one hand (7–9), a rise in barometric pressure may also cause headaches (10). Most passenger cabins in regular airliners are not pressurized to sea level. Furthermore, other factors within the cabin, such as reduced oxygen, noise created by the engines, poor quality of recirculated air, or tension, may induce headaches. We set out to investigate the prevalence and characteristics of FAHA in a large group of adults.
Patients and methods
This prospective study was carried out at the travel clinic of the B’nai Zion Medical Centre in Haifa. The clinic, established in 1992, now attends to 3000–4000 travellers per annum. The clinic provides pre-travel consultation, vaccinations and post-travel care, mostly for travellers to tropical countries.
During the study period (July–September 2006), 1080 sequential travellers were solicited to take part in the study; 12% of these (n = 130) declined participation. The study population thus consisted of 950 travellers (530 men) who were > 18 years old. Following a brief explanation about the study purposes and receipt of an informed consent, each traveller was handed a questionnaire. The opening question excluded from further responses those who had never flown in an airplane or had flown only once in their lifetime.
The questionnaire included three sections: (i) demographics; (ii) details of the nature of headaches in general, and FAHA in particular; and (iii) questions attempting to uncover the causes of FAHA. Those who responded positively in section (ii) to the question: ‘do you suffer from headaches during flights or soon thereafter?’ were asked to continue and describe these headaches. The following headache characteristics were recorded: family history, age of onset, length of symptom (years), severity (on a scale of 1–10), whether it was uni- or bilateral, and length of pain after takeoff or landing. When there was no information regarding a certain parameter, the data were recorded as ‘not available’, and the case in question was excluded from the denominator for that particular parameter only in the analysis. Numerical values of data were recorded when available.
Statistics
We used the statistical features of Microsoft's Excel™ to calculate rates, means and standard deviations. The Instat® software (GraphPad, San Diego, CA, USA) was used to compare means (Student's t-test) or categorical variables (Fisher's exact, or χ2 tests), and calculate relative risk.
Results
The questionnaires were distributed to 950 consecutive travellers who consented to participate. Forty-four (4.6%) were excluded on a ‘single-flight’ experience basis, leaving 906 evaluable travellers (Fig. 1).
FAHA and gender in eligible travellers. FAHA, flight-associated headache.
Demographics and flight habits
This cohort included 507 males (56%), with a mean age of 33.3 ± 14.2 years (range 18–91 years). Forty per cent indicated that they had had 0–10 flights during their lifetime, and 27.6% had had 11–20 flights. The great majority of participants (97.2%) travelled economy class.
Headaches in the entire cohort
Non-flight headaches occurred at least once per month (disregarding flights) in 194 (22.3%) of the participants (Table 1). However, this rate was significantly higher in the FAHA group (51.1%) as opposed to the rest of the cohort (20.9%; P < 0.0001). Twenty-three of the 194 (11.8%) had been given the diagnosis of ‘migraine’, in three others ‘sinusitis’ was the cause of headaches, and in three more the cause was ‘hypertension’. The mean age of onset of these headaches was 9.9 ± 20.8 years, and the mean score of pain on a scale of 1–10 was 6.0 ± 2.2.
Characterization of patients with FAHA (n = 52)
Rates were calculated only for valid responses.
FAHA, flight-associated headache.
Characteristics of the flight-associated headache group
FAHA occurred in 52 travellers (5.7%), of whom 34 (65.4%) were women (Table 1). In contrast, among those without FAHA (n = 854), only 42.7% (n = 365) were women (P = 0.0023). The mean age of those suffering from FAHA (13.8 ± 33.2) was not significantly different from the rest of the group (33.3 ± 14.2).
Comparison of FAHA with ‘regular’ headaches (>1 per month)
The rate of frequent headaches (one or more per month) in the FAHA group was 51.1%, and 10 of them were migraineurs. The rate of frequent headaches in the control group (n = 173) was 20.9%. The rate of migraine was somewhat higher in the FAHA vs. the control group (19.2% vs. 15%, P = NS). There was a significant difference in the laterality of pain between the two groups. Whereas in the FAHA group most headaches were bilateral, those in the ‘frequent headache’ group were unilateral (72.7%, P = 0.019, Fisher's).
Pain characterization in the FAHA group
Ten respondents (19.2%) indicated that the pain appeared on each and every flight. Nineteen described the pain as occurring both on takeoff and landing, whereas in 21 it happened solely upon landing. Almost half (48%) of those suffering from FAHA took analgesics, mostly paracetamol.
A family history of headache was elicited in 13 (32%) of the FAHA group, compared with 26 (14.9%) of the control group (relative risk = 2.17, P = 0.018).
Discussion
The present study found that FAHA affects 5.7% of those who fly. Extrapolation, on the basis of 3.3 billion seats offered annually on commercial flights (http://www.oag.com accessed 14/8/2007) (11) with an occupancy of 70%, gives a figure of > 100 million who suffer from FAHA. This finding has enormous impact, both in terms of suffering and economics. Even if we consider that only 31 of 52 patients constantly took medications to alleviate their headaches during flights, the figures still pose a huge and painful problem.
We found that those who are at risk for FAHA can be identified and characterized. For example, almost two-thirds were women, and one-third reported a family history. Women are known to suffer from headaches more frequently than men (12–16). The familial predisposition is well known. Montagna et al. have found that the rate of headache in family members increases 2.1–3.9 times if one member suffers from headache (17). Similar findings have been reported by a Serbian study (18). Future studies could focus on these high-risk groups and alleviate their distress.
The mechanism of FAHA could not be determined in our study, but we found FAHA to be associated with migraines. One-fifth of the study group reported migraines, and all were women. Notably, the rate of migraine in the general population is lower and stands at 6% in men and 15% in women (19). Nevertheless, other factors, such as the change in barometric pressure, the lower partial pressure of O2, the constant noise of the engines and the lower air quality caused by recirculation, all seem plausible hypotheses. The possible link of FAHA to migraines certainly reflects on the suggested treatment: for example, advocating pre-flight prophylaxis.
The question arose whether FAHA is caused by the change in barometric pressure. A recent publication in the New England Journal of Medicine supports this possibility (20). We found that almost a quarter of FAHA patients had worsening of the headaches upon ascent, and one-fifth upon descent to the Dead Sea (–400 m below sea level), which clearly implies an association. This association has recently been suggested (21), although the exact relationship is yet to be determined. Cottrell (22) has found an association between the barometric pressure in the cabin and the partial pressure of inhaled oxygen. It is also known that hypoxaemia may cause headaches (23–25).
What is the course of FAHA over the years? The present study was not prospective by nature, but it failed to find an improvement over the years. Other studies not focusing on FAHA have in fact found a decrease of headaches in menopausal women. The persistence of FAHA over the years could attest to the mechanism/aetiology. It cannot be excluded that these people diminish their flights in order to avoid the pain. Headaches have an enormous effect on daily living (26), with a decline in quality of life (27). Businesspeople who suffer from FAHA and need to fly often are prone to disability and inability to concentrate, which may affect their choice of work (28).
This study has inherent limitations. As this cohort approached our travel clinic seeking vaccination to tropical countries, most were young adults. We may have missed many older business travellers flying to Europe or the USA. As only 18 of the present cohort flew business class, too small a group on which to draw conclusions. Future studies should address this segment also. The retrospective nature of this study is flawed by the known problems of this type of study (recall bias, etc.). Finally, we would have liked to elaborate on the preventive and therapeutic aspects of FAHA, which will be possible in a prospective trial.
In conclusion, this is the first comprehensive study of the rate and associations of FAHA. FAHA seems to affect a significant number of the travel population. Those at risk for FAHA and the features of FAHA were delineated. Future studies should address the underlying mechanisms and therapeutic options.
Competing interests
None to declare.
Footnotes
Acknowledgements
The authors are grateful to Karl Neumann, MD and H. Neumann for reviewing the manuscript.