DMDM Hydantoin

Also known as: Dimethylol dimethyl hydantoin, Formaldehyde releaser

High ConcernpreservativeEWG: 7-9

A formaldehyde-releasing preservative that slowly emits formaldehyde — a known carcinogen — into the product.

How it works

DMDM Hydantoin works by slowly releasing formaldehyde, which prevents microbial growth. The formaldehyde released is a IARC Group 1 carcinogen and potent sensitiser. While concentrations are typically low (the released formaldehyde is usually 0.01–0.1%), repeated exposure can cause contact allergy and sensitisation, particularly in leave-on products.

Avoid if

Everyone — particularly formaldehyde-sensitive individualsLeave-on products

Commonly found in

ShampoosConditionersSome moisturizers

Safety & restrictions

Releases formaldehyde — IARC Group 1 carcinogen. Contact allergen and sensitiser. Hair care brands have faced lawsuits over DMDM hydantoin in products with reported hair loss. Choose formaldehyde-free preservatives.

Restricted / banned in:EU (restricted — formaldehyde release above 0.2% must be labelled)

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For informational purposes only. Not medical advice. Consult a dermatologist for personalised guidance.