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We read the report by Hollund et al with great interest.1 We agree that there is limited information about the prevalence of airway symptoms caused by highly reactive chemicals in hairdressing salons. In this well designed study, authors focused on age as a risk factor and observed an increased prevalence of respiratory symptoms among the oldest and youngest hairdressers and observed more symptoms among hairdressers over 40 years of age.
Work intensity, work duration, working conditions, and job titles (master, and fellow hairdresser) should also be considered as risk factors for occupational asthma and respiratory symptoms. With the exception of work intensity, these features have been reported as risk factors in previous studies.2–4 Work intensity is an objective parameter for evaluating occupational exposures. In our study, we calculated work intensity from the average number of chemical applications per week (bleaching, dye, and permanent wave) and observed a 3.6 times higher risk of occupational asthma among hairdressers with high work intensity (95% CI 1.2 to 10.9) with a significant trend (χ2trend 4.9, p = 0.027).5 However, we did not observe any excess by work duration, which probably is a result of the healthy worker effect. Hollund et al stated that the older hairdressers had more customers than the younger ones, which may be evidence of higher occupational exposures. If they had used work intensity as a more objective criterion than age, they might have prevented possible misclassifications by age.
Working conditions of hairdressers and exposures depend on country and regional variability, which might also affect study results. In the United States and United Kingdom, the term “hairdressers” is inclusive, denoting women's hairdressers and barbers for men.6 In Turkey, however, the term addresses women's hair salons only. Most of the studies on hairdressers have been published from Nordic and industrialised countries.7–11 Studies from developing countries will help to describe the extent of occupational health problems among hairdressers and to identify aetiological factors.