Methylisothiazolinone contact allergy and dose-response relationships

Area of Science:

• Dermatology
• Toxicology
• Cosmetic Science

Background:

• Methylisothiazolinone (MI) is a preservative increasingly associated with contact allergies.
• The eliciting threshold for MI-induced contact allergy is not well-established.
• Phenoxyethanol enhances MI's antimicrobial properties but its effect on MI allergy is unknown.

Purpose of the Study:

• To determine the eliciting doses of MI contact allergy using patch testing and repeated open application tests (ROAT).
• To investigate if phenoxyethanol influences reactivity to MI in patch tests.

Main Methods:

• Eleven individuals with known MI allergy underwent patch testing with MI and MI plus phenoxyethanol.
• A ROAT simulated exposure to cosmetic cream containing 100, 50, or 5 ppm MI.
• Dose-response relationships were analyzed for both testing methods.

Main Results:

• Phenoxyethanol did not alter the allergic reactions to MI.
• The lowest eliciting dose of MI in patch tests was 1.47 µg/cm(2).
• In ROAT, 64% reacted to 0.21-0.105 µg/cm(2) and 18% reacted to 0.0105 µg/cm(2) (5 ppm MI).

Conclusions:

• A significant percentage of MI-allergic patients react to concentrations much lower than the maximum permitted in cosmetics (100 ppm).
• The study highlights the potential for lower concentrations of MI in cosmetics to elicit allergic reactions.
• Recommendations include reducing MI concentrations in products and close monitoring of MI contact allergy development.