The methylisothiazolinone epidemic goes along with changing patients' characteristics – After cosmetics, industrial applications are the focus

Background Sensitization to methylisothiazolinone (MI) has seen an exceptional epidemic, mainly attributed to its use in cosmetics. Objectives To trace the epidemic of MI allergy (2009–2018), and to analyze a possible change of patients' characteristics. Methods Informationsverbund Dermatologischer Kliniken‐data of patients patch tested between 2009 and 2018 with MI (0.05% aq.) were analyzed concerning anamnestic items and sensitization frequencies. Results Overall, 4.9% reacted positive to MI. Comparing sensitization to MI in three periods (2009, 2013/14, and 2017/18), there was an increase to 7% in 2013 and a decrease to 3.4% in 2018. The MOAHLFA Index (M=Men, O=Occupational Dermatitis, A=Atopic Dermatitis, L=Leg Dermatitis, F=Face Dermatitis, A= Age > 40) for the period 2013/14 is characterized by a lower proportion of occupational dermatitis and a higher proportion of face dermatitis. The period 2017/18 is characterized by increases of occupational dermatitis and hand dermatitis, and a decrease of face dermatitis. Painters, personal care workers, and hairdressers were particularly affected. Sensitization in hairdressers and personal care workers (mostly cosmeticians) decreased after the peak in 2013/14, whereas sensitization to MI in painters continued to increase. Conclusions After an unprecedented epidemic of MI allergy, mainly caused by its use in cosmetics, the continuous use of MI in industrial applications, for example, paints, and subsequent sensitization remain a matter of concern. Highlights After an epidemic of MI allergy mainly caused by its use in cosmetics, the continuous use of MI in industrial applications, for example, paints, and subsequent sensitization remain a matter of concern.