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DMDM Hydantoin

Worth knowingPreservativepreservative

EU-restricted, a common contact allergen, or subject to live debate.

Also written as: 1,3-Bis(hydroxymethyl)-5,5-dimethylimidazolidine-2,4-dione · Dimethylol Dimethyl Hydantoin

What it is

DMDM hydantoin works by slowly releasing small amounts of formaldehyde into the product, which is what kills the microbes. It is still a permitted EU preservative, but formaldehyde itself was banned as a cosmetic ingredient in 2019, and since 2022 the EU has required a 'releases formaldehyde' warning at a much lower threshold than before. It is now uncommon in European skincare and more often seen in imported or older formulations.

What it does well

  • Broad-spectrum and stable across a wide pH range

    It is particularly effective against Gram-negative bacteria and does not need an acidic formula, which is why it was historically popular in shampoos and lotions.

    Moderate evidence

Worth knowing

  • Releases formaldehyde, a Group 1 human carcinogen by inhalation

    The amounts released in a cosmetic are small and the cancer classification relates to inhaled occupational exposure, not skin contact with a mask. The practical skin issue is allergy, not cancer.

    Matters most toPeople who prefer to avoid formaldehyde exposure of any kind.

  • A recognised contact allergen

    A 2026 systematic review and meta-analysis of 158 studies and over 1.3 million dermatitis patients found a pooled prevalence of DMDM hydantoin allergy of 1.37%, alongside 2.88% for formaldehyde itself.

    Matters most toPeople with known formaldehyde allergy: they need to avoid all formaldehyde releasers, not just formaldehyde.

Where the EU stands

Concentration-restricted

Permitted preservative up to 0.6%. Because it releases formaldehyde, any finished product containing it must be labelled 'releases formaldehyde' if free formaldehyde exceeds 0.001% (10 ppm), a threshold lowered from 0.05% by Regulation (EU) 2022/1181, applying from 31 July 2024.

Regulation (EC) No 1223/2009, Annex V entry 33; labelling rule in the preamble to Annex V as amended by Commission Regulation (EU) 2022/1181 · source ↗

Sources (2)

Every link goes to the original: a journal, a PubMed record or an EU document.

  1. [1]
    The Prevalence of Contact Allergy to Formaldehyde and Formaldehyde Releasers: A Systematic Review and Meta-Analysis

    Contact Dermatitis · 2026 · doi:10.1111/cod.70172

    Across 158 studies and 1,347,638 dermatitis patients, pooled contact allergy prevalence was 2.88% for formaldehyde and 1.37% for DMDM hydantoin; the authors note formaldehyde and quaternium-15 have been prohibited in the EU since 2019 while DMDM hydantoin has not.

  2. [2]
    Contact dermatitis associated with preservatives: Retrospective analysis of North American Contact Dermatitis Group data, 1994 through 2016

    Journal of the American Academy of Dermatology · 2021 · doi:10.1016/j.jaad.2020.07.059

    Formaldehyde and formaldehyde-releasing preservatives were among the most frequent preservative allergens, with formaldehyde itself positive in 7.8% of patients tested.