Methylisothiazolinone contact allergy: a review

Area of Science:

• Dermatology
• Toxicology
• Cosmetic Science

Background:

• Methylisothiazolinone (MI) transitioned from combination use with MCI to standalone preservative in industrial and cosmetic products since the early 2000s.
• MCI/MI mixtures are known potent sensitizers, with MI also identified as a significant sensitizer.
• The prevalence of MI contact allergy is rising, with exposure sources including occupational, cosmetic, and household products.

Purpose of the Study:

• To investigate the prevalence and concentration of MI in cosmetic products.
• To assess the reactivity of allergic patients to varying MI concentrations found in consumer products.

Main Methods:

• Analysis of 1272 cosmetic products for MI labeling.
• Quantification of MI concentrations using high-performance liquid chromatography with UV and mass spectrometry detection.
• Evaluation of patient reactions to MI concentrations, including levels found in products.

Main Results:

• MI was found in 1.5% of analyzed cosmetic products, predominantly rinse-off types.
• Detected MI concentrations ranged from 2 to 100 ppm.
• A significant number of MI-allergic patients reacted to 50 ppm MI, a level below the maximum permitted concentration in cosmetics.

Conclusions:

• The increasing prevalence of MI contact allergy, evidenced by patient reactions to common product concentrations, warrants close monitoring.
• Inclusion of MI in the European Baseline Series for allergy testing is recommended.
• Potential for an epidemic of MI contact allergy necessitates ongoing surveillance and risk assessment.