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Diazolidinyl Urea

Worth knowingPreservativepreservative

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

Also written as: Germall II · N-(Hydroxymethyl)-N-(dihydroxymethyl-1,3-dioxo-2,5-imidazolidinyl-4)-N'-(hydroxymethyl)urea

What it is

Diazolidinyl urea is a more active successor to imidazolidinyl urea, releasing more formaldehyde and therefore working at lower concentrations. It is still permitted in the EU at up to 0.5% but is now rare in European skincare, partly because of the formaldehyde labelling rule and partly because of its allergy profile.

What it does well

  • Strong, pH-independent antibacterial protection

    More potent than imidazolidinyl urea, so lower use levels achieve the same protection in emulsions and lotions.

    Moderate evidence

Worth knowing

  • Higher formaldehyde release than the older ureas, and correspondingly more allergy

    Pooled contact allergy prevalence was 1.42% in the 2026 meta-analysis, above imidazolidinyl urea and DMDM hydantoin.

    Matters most toPeople with formaldehyde allergy or a history of preservative dermatitis.

  • Triggers the formaldehyde warning label

    Products must be marked 'releases formaldehyde' if free formaldehyde exceeds 10 ppm in the finished product.

    Matters most toAnyone screening labels for formaldehyde.

Where the EU stands

Concentration-restricted

Permitted preservative up to 0.5%. As a formaldehyde releaser, products containing it must carry the warning 'releases formaldehyde' where free formaldehyde exceeds 0.001% (10 ppm).

Regulation (EC) No 1223/2009, Annex V entry 46; labelling rule in the preamble to Annex V as amended by Commission Regulation (EU) 2022/1181 · source ↗

Sources (1)

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

    Pooled contact allergy prevalence for diazolidinyl urea was 1.42%; the authors note it remains permitted in the EU while formaldehyde and quaternium-15 do not.