Prevalence of Contact Allergy to Isothiazolinones in Dermatitis Patients From 2000 to 2025: A Systematic Review and Meta‐Analysis

Isothiazolinones are employed in the preservation of cosmetic, consumer and industrial products, with the objective of preventing deterioration and spoilage. However, the utilization of isothiazolinones is associated with an elevated risk of developing contact allergy (CA). Herein, we assess the epidemiology of CA to isothiazolinones among dermatitis patients from year 2000 onwards. We systematically searched PubMed, Embase, and Web of Science from 1 January 2000 to 19 April 2025 yielding 115 studies comprising 1 514 781 dermatitis patients. The prevalence of CA to methylchloroisothiazolinone/methylisothiazolinone (MCI/MI) was 4.58%, methylisothiazolinone (MI) was 5.48%, and benzisothiazolinone (BIT) was 2.09%. The clinical relevance ranged from 60.1% for MCI/MI, 55.6% for MI, and 35.3% for BIT. Asia and North and South America exhibited the highest rates of CA to isothiazolinones, whereas Europe showed lower rates. These findings underscore the efficacy of proactive risk management for post-marketed substances such as MI, underscoring substantial regional variations in usage patterns, which are contingent on the strictness or permissiveness of their incorporation into everyday consumer products. There is an indication of a decline, particularly regarding MI and MCI/MI. However, there has been an increase in the use of substances such as BIT, which necessitates enhanced surveillance measures.