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Allergic Contact Dermatitis — SCE Dermatology MCQ

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ModerateInflammatory DermatosesAllergic Contact DermatitisSCE Dermatology

A 35-year-old woman has chronic hand eczema. Patch testing using the European baseline series shows a strongly positive (+++) reaction to methylisothiazolinone (MI) at day 4. She works as a hairdresser and uses various leave-in hair products. What is the significance of this finding?

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Correct answer: D — MI is a preservative in rinse-off and leave-on cosmetics and is likely causing her eczema

Methylisothiazolinone (MI) is a preservative that has become one of the most common contact allergens, particularly since its increased use in cosmetics and personal care products following EU restrictions on MI/MCI combination. It was named Contact Allergen of the Year by the ACDS in 2013. A strongly positive patch test reaction at day 4 is a true allergic response. Hairdressers are exposed through hair care products. Following EU regulation, MI was banned from leave-on cosmetic products in 2016 and restricted in rinse-off products, but older stock or non-EU products may still contain it.

Reference: BAD 2017 Contact Dermatitis Guidelines; BJD 2015 MI epidemic