Cited skincare — every flag names its source, no upsell.

Methylisothiazolinone

Synthetic preservative once ubiquitous in wash-off products; banned/restricted in leave-ons after a global allergic-contact-dermatitis epidemic.

What it does

Methylisothiazolinone (MI) is a broad-spectrum biocide that surged in cosmetic use after parabens fell out of favor in the late 2000s. Within years, MI became one of the most-cited contact allergens in dermatology patch-test surveys — within years it became one of the most-cited contact allergens in dermatology patch-test surveys. It has since been restricted in leave-on cosmetics in the EU and restricted concentrations in rinse-off; US OTC and personal-care products may still contain it. If you've flagged a fragrance or preservative sensitivity, MI is high-priority to avoid even in shampoos and body washes.

The evidence, graded

moderateCommon sensitivity and contact-allergy triggers in skincare include fragrance (the most-cited cosmetic allergen), essential oils, denatured alcohol, and certain preservatives (methylisothiazolinone, formaldehyde-releasers). Patch test new products on the inner forearm for 48–72 hours before face-wide use.Warshaw 2020 · Dermatitis ↗

Graded per the methodology: strong · moderate · emerging · expert consensus. A weak source on a strong claim gets the weaker label.

Also known as

MI, MIT

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