Cited skincare — peer-reviewed evidence, no upsell.

DMDM Hydantoin

Preservative that works by slowly releasing formaldehyde. A recurring patch-test allergen, especially for formaldehyde-sensitized skin.

What it does

DMDM hydantoin keeps water-based formulas free of bacteria and mold by releasing small amounts of formaldehyde over the product's life. That mechanism is also its liability: North American patch-test surveillance records consistent positive reactions to it, and people sensitized to formaldehyde tend to react to the whole releaser class. It is most common in shampoos, conditioners, and other rinse-off products, with occasional leave-on use. Well tolerated by most people; worth avoiding if you've flagged a preservative or fragrance sensitivity.

The evidence, graded

strongCommon 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

DMDM

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