Isothiazolinone Sensitization in Gran Canaria (Spain). A Follow-up of 20 Years

Isothiazolinones are responsible for an epidemic of allergic contact dermatitis across Europe over the past 2 decades. Regulatory restrictions on methylisothiazolinone (MI) in cosmetics have been followed by declining sensitization rates in surveillance networks. Benzisothiazolinone (BIT) and octylisothiazolinone (OIT) have emerged as sensitizers of growing clinical relevance.

To characterize temporal trends in sensitization to MCI/MI, MI, BIT, and OIT over more than 2 decades at a single center in Gran Canaria, Spain.

Cross-sectional study of patients patch-tested between 2003 and 2025. Temporal trends were analyzed using univariate analysis and generalized additive logistic regression models adjusted for age, sex, atopic dermatitis, and occupation.

Sensitization rates were 11.1% for MCI/MI, 11.6% for MI, 7.6% for BIT, and 0.9% for OIT. MCI/MI and MI sensitization peaked around 2014-2015 and 2020-2021, respectively, then declined following European cosmetic regulatory restrictions. BIT sensitization showed a flatter, sustained trend and was independently associated with older age, male sex, and absence of atopic dermatitis.

There has been a decline in MCI/MI and MI sensitization after regulatory restrictions on cosmetic application. BIT is an emerging isothiazolinone of concern with a distinct occupational profile, warranting regulatory attention to household cleaners and industrial sources.