Contact sensitization to methylisothiazolinone in Finland--a multicentre study.

Area of Science:

• Dermatology
• Allergology
• Cosmetic Science

Background:

• Antimicrobials are a common cause of cosmetic-related contact allergies.
• Methylisothiazolinone (MI), previously combined with MCI, is now approved for standalone use in cosmetics and industrial products.
• MCI is an extreme-strong sensitizer, while MI is classified as a strong-moderate sensitizer.

Purpose of the Study:

• To investigate the prevalence of positive patch test reactions to MI in Finland.
• To assess the relationship between MI sensitivity and MCI/MI sensitivity.
• To evaluate the clinical relevance of MI allergy.

Main Methods:

• A 3-year patch testing study (2006-2008) involving 10,821 patients across eight Finnish clinics.
• Testing concentrations of MI included 0.1% (1000 ppm) and 0.03% (300 ppm).
• Positive MI reactors underwent a repeated open application test (ROAT) during 2008.

Main Results:

• Positive patch test reactions to 0.1% and 0.03% MI were observed in 1.4% and 0.6% of patients, respectively.
• 66% of MI-positive patients also reacted to MCI/MI.
• 10 out of 33 patients (30%) undergoing ROAT showed positive results.

Conclusions:

• Methylisothiazolinone (MI) used independently can induce contact allergy.
• The findings highlight the potential for MI to cause allergic reactions when used alone in cosmetics.
• Continued surveillance is necessary to confirm the safety profile of MI in cosmetic applications.