Is DMDM hydantoin safe? What a formaldehyde releaser is and where it is limited

Cosmetic preservative (formaldehyde releaser) · Also known as: DMDM Hydantoin, 1,3-Dimethylol-5,5-dimethylhydantoin, Dimethylol dimethyl hydantoin, 1,3-Bis(hydroxymethyl)-5,5-dimethylimidazolidine-2,4-dione, CAS 6440-58-0, EC 229-222-8 · Reviewed Oct 20, 2026 · 22 sources

Where DMDM hydantoin is allowed

What is DMDM hydantoin?

DMDM hydantoin is a preservative that works by releasing formaldehyde. Health Canada says such ingredients slowly release very small amounts of formaldehyde to preserve the product.

It belongs to a family: FDA's list of common cosmetic allergens names it alongside diazolidinyl urea, imidazolidinyl urea and quaternium-15, and Washington State's rule lists the same four. The Cosmetic Ingredient Review (CIR) panel calls this a slow, irreversible release, unlike the fast formaldehyde and methylene glycol balance in some other products.

Why it's used, and where you'll find it

Health Canada notes that cosmetics sit in warm, damp bathrooms where microorganisms thrive, so most contain preservatives. The EU's scientific committee (the SCCS) cited surveys finding formaldehyde releasers, as a group, in 7.9% of 4,680 German cosmetics and 23.8% of 8,057 US products.

• skin-care products and moisturisers
• hair-care products
• other leave-on and rinse-off cosmetics

What the research and regulators say

What the cancer classification of formaldehyde means

IARC lists formaldehyde in Group 1, 'carcinogenic to humans'. Its latest evaluation (Monographs Volume 100F, working group met 2009, published 2012) found sufficient human evidence that formaldehyde causes cancer of the nasopharynx and leukaemia, and a positive association with sinonasal cancer, from studies of workers such as industrial workers and embalmers. IARC says its classifications describe the strength of the evidence, not the level of risk. Health Canada says formaldehyde inhaled at high levels is anticipated to be a human carcinogen, but small amounts on the skin mean very low exposure and, in its words, 'no health risk'. IARC evaluated formaldehyde, not DMDM hydantoin; we found no regulator conclusion that DMDM hydantoin causes cancer at cosmetic levels. ^{[6, 9, 10, 11]}

Skin allergy in people allergic to formaldehyde

The SCCS says formaldehyde from releasers can trigger allergic contact dermatitis in people already allergic to it. In a 2016 double-blind study, 15 formaldehyde-allergic volunteers and 12 controls used DMDM hydantoin moisturisers for four weeks on skin pre-irritated with a detergent. A moisturiser releasing at least 40 ppm formaldehyde (made with 0.6% DMDM hydantoin, the EU maximum) caused reactions in 9 of the 15 allergic volunteers and none of the controls; one releasing 2.5 to 10 ppm caused none. In a 1988 study, 4 of 12 formaldehyde-allergic patients developed dermatitis after a week using a cream with 1% DMDM hydantoin. A North American patch-test review found most formaldehyde-allergic patients were not allergic to DMDM hydantoin or two related releasers. ^{[8, 12, 13, 14]}

Why the EU tightened its warning rule, and what the industry panel says

In 2021 the SCCS advised that the old warning trigger of 0.05% (500 ppm) did not sufficiently protect formaldehyde-sensitised consumers, and that 10 ppm would protect the vast majority; its advice covered skin sensitisation only. The Cosmetic Ingredient Review (CIR) panel, funded by the cosmetics trade association (which says it works independently), lists DMDM hydantoin as safe as used at up to 1% in its quick-reference table, citing a 1988 report and noting 'confirmed 09/05'. That report's abstract says mutagenicity results varied by test system. In 2021 the panel said it would speed up a re-review of DMDM hydantoin; we could not find the outcome. The EU cap is 0.6%. ^{[7, 8, 16, 18, 21, 22]}

Who might choose to avoid it

People with a known formaldehyde allergy are the group the clinical studies and the SCCS point to, and the EU warning exists for them. We found no other group singled out.

How to spot it on a label

Look for 'DMDM Hydantoin' (CAS 6440-58-0) in the ingredient list. Other releasers appear under their own names, such as diazolidinyl urea, imidazolidinyl urea and quaternium-15. Some EU packs also say 'releases formaldehyde'.

Frequently asked questions

Related ingredients

• Phenoxyethanol
• Methylparaben (and the parabens)
• Fragrance (Parfum)

This page summarizes what regulators and published research say, as of the review date above. Rules and evidence change; check the linked sources for the latest. It is general information, not medical advice — talk to a doctor or pharmacist about your own health.