At a glance
| Chemical family | A formaldehyde-releasing cosmetic preservative (an allantoin-derived urea); sibling to imidazolidinyl urea, DMDM hydantoin and quaternium-15 |
| CAS number | 78491-02-8 |
| Classification | The urea itself is not a classified carcinogen; it releases formaldehyde (IARC Group 1). A weak contact allergen (~1.4% of patch-tested dermatitis patients). EU/UK-restricted with a formaldehyde-warning label |
| Where you encounter it | Lotions, creams, shampoos, hand gels and other water-based cosmetics and personal-care products, as a preservative |
| Sleep micro-environment relevance | A leave-on/rinse-off preservative that transfers onto bedding as a residue; relevant chiefly to formaldehyde-sensitized individuals |
| Activated carbon capture | Not the lever — product choice (formaldehyde-free preservation) and label-reading address it |
What it is
Diazolidinyl urea is an antimicrobial preservative — one of a handful of so-called formaldehyde releasers used to keep water-based cosmetics free of bacterial and fungal growth. Chemically it is derived from allantoin, and it works by slowly decomposing in the product to release a low, steady trickle of formaldehyde, which does the actual preserving. Peer-reviewed — Goossens & Aerts 2022 It is sold under the trade name Germall II, and sits alongside its close relatives imidazolidinyl urea, DMDM hydantoin and quaternium-15.
Of the common urea and hydantoin releasers, diazolidinyl urea releases the most formaldehyde — placing just behind pure paraformaldehyde in measured release, and ahead of its siblings. Peer-reviewed — Lv et al. 2015 That makes it an effective preservative and, simultaneously, the urea releaser that warrants the closest look.
How it relates to the bedroom
The same residue route — with a formaldehyde twist
For the sleep environment, diazolidinyl urea behaves like the rest of the personal-care family: a lotion, cream or gel applied before bed leaves a film on skin that transfers onto sheets and pillowcases. What is distinctive is the slow chemistry that continues in the product and on the skin — the gradual liberation of formaldehyde. Under the right conditions of concentration, warmth and water content, formaldehyde releasers can give off more than 200 ppm formaldehyde, enough to provoke allergic contact dermatitis in a sensitized person. Peer-reviewed — de Groot et al. 2010 Release rises with temperature and storage time — a reason a product can become more reactive over its life. Peer-reviewed — Lv et al. 2015
A weak allergen — but a real one, for some
The honest framing is calibrated. Diazolidinyl urea is a comparatively weak sensitizer: it is positive on patch testing in roughly 1.4% of dermatitis patients, lower than the isothiazolinone preservatives that drove recent allergy epidemics. Peer-reviewed — Goossens & Aerts 2022 For the great majority of people it is unremarkable. But for those already allergic to formaldehyde — or sensitized to the urea itself — it is a genuine trigger, and notably its reactions tend to show up as facial dermatitis, consistent with cosmetic use and, plausibly, with the face's long nightly contact with a pillow. Inferred — urea-releaser sensitization is associated with facial/cosmetic-pattern dermatitis; the pillow-contact link is a reasonable extension
How regulators have responded
The regulatory story makes the formaldehyde distinction concrete. Formaldehyde itself is now prohibited as a cosmetic ingredient in the EU and UK — banned outright after being classified a Category 1B carcinogen. Regulatory — UK SAG-CS Opinion 2022; Cosmetic Regulation 1223/2009 Yet formaldehyde can still legally reach consumers through releasers like diazolidinyl urea, which remains permitted (Annex V, entry 46). To bridge that gap, any finished product that releases formaldehyde above a threshold must carry a "contains formaldehyde" warning — historically set at 0.05%, which regulators have concluded is too high and have moved to lower to 0.001% (10 ppm) to protect formaldehyde-allergic consumers. Regulatory — UK SAG-CS Opinion 2022 The thrust is disclosure and protection of the sensitized, not a ban of the urea.
What the research says
- It is a formaldehyde releaser, not a carcinogen itself. Slowly liberates formaldehyde (IARC 1); that is the antimicrobial mechanism and the hazard. Peer-reviewed — Goossens & Aerts 2022
- The most formaldehyde-active urea releaser. Releases more formaldehyde than imidazolidinyl urea, DMDM hydantoin or quaternium-15. Peer-reviewed — Lv et al. 2015
- A weak contact allergen. Positive in ~1.4% of patch-tested dermatitis patients; can cause facial and airborne dermatitis in the sensitized. Peer-reviewed — Goossens & Aerts 2022
- Regulated by disclosure. Formaldehyde banned as an ingredient; releasers permitted but labelled; threshold being tightened to 0.001%. Regulatory — UK SAG-CS 2022
What helps reduce it
Read labels if you are sensitized. "Diazolidinyl urea" is named on ingredient lists, and a "contains formaldehyde" warning flags release above the threshold. Regulatory — UK SAG-CS 2022
Choose formaldehyde-free preservation. For formaldehyde-allergic people, the practical step is avoiding leave-on products preserved with any of the releasers. Peer-reviewed — de Groot et al. 2010
Launder bedding normally. The residue washes out, and formaldehyde is water-soluble and volatile. Inferred
What does NOT help
- Treating it as a carcinogen to fear. The urea is not a classified carcinogen; the formaldehyde it releases is, but in tiny amounts. The accurate concern is allergy, not cancer risk from cosmetic use. Peer-reviewed — Goossens & Aerts 2022
- Air purifiers. This is a skin-and-product residue and a trace formaldehyde source, not a major airborne pollutant. Inferred
Open research questions
- How much formaldehyde transferred to bedding from leave-on products contributes to facial dermatitis in sensitized sleepers. Speculation
- Whether the tightened 0.001% labelling threshold measurably reduces formaldehyde-allergy flares. Speculation
Citations
- Goossens A, Aerts O (2022). Contact allergy to and allergic contact dermatitis from formaldehyde and formaldehyde releasers: a clinical review and update. Contact Dermatitis. Diazolidinyl urea one of five main releasers; patch-test 2% pet. separately; cause of localized/airborne/generalized dermatitis. Via Consensus. Reference record Peer-reviewed
- Lv C, et al. (2015). Investigation on formaldehyde release from preservatives in cosmetics. Int. J. Cosmetic Science. Release order paraformaldehyde > diazolidinyl urea > DMDM hydantoin ≈ quaternium-15 ≈ imidazolidinyl urea; release rises with temperature and storage. Via Consensus. Reference record Peer-reviewed
- UK SAG-CS Final Opinion on Formaldehyde Releasing Substances (July 2022); EU/UK Cosmetic Regulation 1223/2009. Formaldehyde prohibited as an ingredient (Annex II 1577, Cat 1B carcinogen); diazolidinyl urea permitted (Annex V entry 46); "contains formaldehyde" label above 0.05%, recommended lowered to 0.001%. UK OPSS / SAG-CS Regulatory
Frequently asked questions
Is diazolidinyl urea a carcinogen?
The urea itself is not a classified carcinogen. What makes it noteworthy is that it is a formaldehyde releaser: it slowly decomposes in a product to give off small amounts of formaldehyde, which is the antimicrobial action — and formaldehyde is the IARC Group 1 carcinogen. So the accurate way to describe diazolidinyl urea is as a formaldehyde donor, not as a carcinogen in its own right. The amounts of formaldehyde involved in cosmetic use are very small.
What is it used for?
It is a preservative — sold under the trade name Germall II — used to stop bacteria and fungi growing in water-based cosmetics and personal-care products such as lotions, creams, shampoos and hand gels. Preservatives like this are necessary in water-containing products; without them the product would spoil. Diazolidinyl urea is the most formaldehyde-active of the common urea preservatives, which is why it preserves effectively but also draws the most scrutiny.
Why does it matter in the bedroom?
Like the other personal-care preservatives in this Atlas, it reaches your bed as a residue: a lotion or cream applied before sleep transfers onto sheets and pillowcases. For the large majority of people this is harmless. The group it matters to is the minority already allergic to formaldehyde or to the urea itself, for whom even small residues on bedding or in leave-on products can trigger or sustain contact dermatitis — often on the face, the area in longest contact with a pillow.
Should I avoid it?
Only if you are sensitized. Diazolidinyl urea is a relatively weak allergen — positive in roughly 1.4% of patch-tested dermatitis patients — so for most people it is not a concern. If you have a known formaldehyde or formaldehyde-releaser allergy, the advice is to avoid leave-on cosmetics preserved with it; the ingredient is named on the label, and EU/UK rules add a 'contains formaldehyde' warning above a set threshold. Formaldehyde-free alternatives are widely available.
Related compounds
Embr is a sleep environment company researching and addressing the chemistry of the bedroom. Research and product development in progress.
Last reviewed 2026-06-27. If you find a factual error, contact us.