Table 4.

Epidemiological studies assessing relation between respiratory symptoms/diseases are persulphate/bleach exposure (n = 9 studies, n = 10 publications)

Author, year of publication, country	Study period, study design, respiratory outcome	Methods	N hairdressers	N controls	Main outcomes	Quality assessment Total score*
Hollund et al. (2001), (2003) Norway	1995–1999 Prospective study Respiratory symptoms, atopy	Questionnaire, interview (for exposure assessment), total/specific IgE	91	80 office workers	Hairdressers over 40 years had significantly more symptoms than controls in a model adjusted for atopy and smoking: •Wheezing- 56 vs 24%, respectively, OR 3.3 (95% CI 1.0 to 11) •Breathlessness- 68 vs 33%, respectively, OR 3.9 (95% CI 1.1 to 14) Hairdressers had significantly more symptoms of wheezing, breathlessness, or runny nose from exposure to bleaching powder than controls in a model adjusted for atopy, age, and smoking: 44 vs 3%, respectively, OR 20 (95% CI 4.3 to 96) Hairdressers reported on average 13 chemically treated clients per week In 1999, former hairdressers reported significantly more respiratory symptoms when exposed to bleaching powder, compared with current hairdressers	12.5 12.5
Albin et al. (2002) Sweden	1996–1997 Cross-sectional Asthma	Questionnaire	3957	4905 general population	Moderate effects on risk of asthma were found from hairdressing work (among never-smokers in comparison to controls in a model adjusted for calendar year, hay fever and region of residence: •Asthma incidence 4.4. vs 2.5 per 1000 person-years, respectively, IRR 1.6 (95% CI 1.1 to 2.2) The hairdressers most often performing hair bleaching treatments or using hair spray had, compared with the most infrequent users, a slightly, but not significantly higher incidence of asthma in a model adjusted for calendar year, hay fever, smoking and region of residence: •Bleaching- IRR 1.5 (95% CI 0.7 to 3.0) •Hair spraying- IRR 1.4 (95% CI 0.8 to 2.4) Two or more bleaching procedures per week reported 69% of hairdressers, 8 or more procedures 10%	13
Iwatsubo et al. (2003) France	1994–1997 Prospective study Respiratory symptoms, lung function	Questionnaire, spirometry, NSIC, expert workplace description	297 apprentices	248 office apprentices	In the initial phase, respiratory symptoms were significantly less frequent and lung function was better among hairdressing apprentices In the final phase, there was the same result for respiratory symptoms, but significant deterioration of lung function was found in hairdressing apprentices compared to controls. There was no significant correlation between change in lung function and specific hairdressing activities, including frequency of bleaching One or more bleaching procedure per day reported 41% of apprentices, 5 or more procedures 8%	14
Hashemi et al. (2010) Iran	Cross-sectional Respiratory symptoms, lung function	Questionnaire, spirometry	50	50 office workers	All respiratory symptoms (cough, breathless, wheezing, and phlegm) were significantly more prevalent in the hairdressers than in the control group (P < .001). Hairdressers reported that bleaching powder and hair spray were the most irritant chemicals that provoke respiratory symptoms. The impaired lung function tests in hairdressers followed symptom data	9.5
Lysdal et al. (2014) Denmark	1985–2007 Prospective cohort Respiratory symptoms	Questionnaire	5324 (all hairdressing graduates in study period)		Shortness of breath due to bleaching was reported in 27.1%; more ex-hairdressers ever had respiratory reaction to bleaching ( 30.2%) than current hairdressers (17.6%, OR 2.02, 95% CI 1.77–2.31). Respiratory reaction to bleaching was found significantly more in hairdressers with adulthood onset asthma (57.5%) than in hairdressers with childhood asthma (38.1%), and without asthma (24.4%)	13.5
Hassan and Bayomy (2015) Egypt	Cross-sectional Respiratory symptoms	Questionnaire	80	50 office workers	Hairdressers were more likely to report wheezes, chest tightness and cough than office workers (23.8 vs 8.0, 21.3 vs 8.0, and 25.0 vs 10%, respectively; p = 0.02, 0.04, and 0.03, respectively). Hairdressers who were more likely to report symptoms than controls were older, with higher body mass index and longer duration of work There were no significant associations between frequent bleaching and respiratory symptoms. One or more bleaching procedures per day reported 64% of hairdressers, 5 or more procedures 29%	10
Nemer et al. (2015) Palestine	2008–2013 Prospective study Respiratory symptoms, lung function	Questionnaire, spirometry, NH3 measurement	170 (initial phase) 161 (follow-up)		Current hairdressers developed more respiratory symptoms and larger lung function decline than former hairdressers during follow-up Hairdressers who applied bleaching more than 5 times per week showed a non-significant stronger decline of FEV1 compared with those who applied it less than 5 times per week. Five or more bleaching procedures per week reported 38% of hairdressers	15
Norlien et al. (2017) USA	2012 Cross-sectional Respiratory symptoms	Questionnaire	2058		Respiratory symptoms were reported by 46%. Relationship between asthma diagnosis and exposure results was not found. Use of bleach was reported by 87.3%	7.5†
Foss-Skiftesvik et al. (2017) Denmark	Cross-sectional Rhinitis, asthma	Questionnaire	504 apprentices	1400 general population	The 1-year prevalence of rhinitis symptoms was higher in hairdressing apprentices than in controls: •58.1% vs 46.6%, respectively, crude OR 1.59 (95%CI 1.30–1.98) Asthma symptoms were equally common. These findings were confirmed in models adjusted for smoking, education level, and degree of rurality Bleaching products were the most frequently reported cause of rhinitis and asthma symptoms in hairdressing apprentices	13.5

OR odds ratio, IRR incidence risk ratio, CI confidence internal, FEV₁ forced expiratory volume in the first second, IgE immunoglobulin E, NSIC nonspecific inhalation challenge

*Maximum score = 15; scores ≥ 70% of maximum score are in bold

†Studies with the indicated risk of bias