Contact allergy to hair cosmetic allergens in Thailand

Background Hair cosmetics such as hair dyes, bleaching, waving, and cleansing products are composed of numerous chemical ingredients. Allergic reactions to these contact allergens, other than p-phenylenediamine, are rarely reported. Objectives To study the incidence of patch test reactions to hair cosmetic allergens and identify the factors associated with hair cosmetic allergy in Thailand. Methods We retrospectively reviewed the case records of patients who underwent patch testing from 2009 to 2018. Patients with at least one positive patch test reaction to a potential contact allergen associated with hair cosmetic ingredients were studied. Results Overall, 2842 patients were patch tested. Of the hair cosmetic allergen categories, preservatives had the highest rate of positive reactions, followed by surfactants and hair dyes. Perming agents were less problematic in comparison. The hands, head, and neck were the predominately affected sites of allergic reactions to hair cosmetic ingredients. Conclusions Preservatives, surfactants, and hair dyes are important contact allergens, whereas perming agents are less likely to cause allergic reactions. Hair cosmetic ingredients are regulated by national agencies, which influences their extent of exposure and rates of contact allergies. Further continuous observation of hair cosmetic allergy is needed to provide the best patient care.