At a glance
| Chemical family | A formaldehyde-releasing cosmetic preservative (an allantoin-derived urea); milder sibling of diazolidinyl urea, related to DMDM hydantoin and quaternium-15 |
| CAS number | 39236-46-9 |
| Classification | The urea itself is not a classified carcinogen; it releases formaldehyde (IARC Group 1). The weakest contact allergen of the common releasers (~1.2% of patch-tested dermatitis patients). EU/UK-restricted with a formaldehyde-warning label |
| Where you encounter it | Lotions, creams, shampoos, makeup 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
Imidazolidinyl urea is an antimicrobial preservative in the formaldehyde-releaser class, used to keep water-based cosmetics free of microbial growth. Derived from allantoin, it preserves by slowly decomposing to liberate a small, steady amount of formaldehyde. Peer-reviewed — de Groot et al. 2010 Sold as Germall 115, it is the gentler counterpart to diazolidinyl urea (Germall II); the two are chemically close, share decomposition products, and cross-react in allergic individuals.
What sets imidazolidinyl urea apart within the family is that it is the mildest of the common releasers — it gives off less formaldehyde than diazolidinyl urea and carries the lowest contact-allergy prevalence of the group. Peer-reviewed — Karimian et al. 2026
How it relates to the bedroom
A personal-care residue, like the rest of its class
For the sleep environment the pathway is familiar: a lotion, cream or shampoo used before bed leaves residue on skin that transfers onto sheets and pillowcases, carrying with it the slow formaldehyde release that continues in the product. Roughly one in five cosmetics in the US has historically contained a formaldehyde releaser of some kind, so it is a common, if low-level, presence. Peer-reviewed — de Groot et al. 2010 As with the other releasers, the right combination of concentration, warmth and water can push formaldehyde release above 200 ppm — the level at which a sensitized person may react. Peer-reviewed — de Groot et al. 2010
The mildest of a weak class
Calibrated honestly, imidazolidinyl urea is the least troublesome of the urea releasers. A meta-analysis of more than 1.3 million patch-tested dermatitis patients put its contact-allergy prevalence at 1.20% — the lowest of the five common releasers, below diazolidinyl urea (1.42%) and quaternium-15 (1.89%). Peer-reviewed — Karimian et al. 2026 For the general population it is a non-issue. Where it matters is the same narrow group as its siblings: people allergic to formaldehyde or to the urea itself, in whom leave-on residues — including those left on a pillow overnight — can sustain a facial or hand dermatitis. Inferred — urea-releaser sensitization presents in a cosmetic/facial pattern; the overnight pillow-contact contribution is a reasonable extension Because it cross-reacts with diazolidinyl urea, someone reacting to one should treat both as off-limits. Peer-reviewed — Karimian et al. 2026
The regulatory frame
The regulation mirrors that of its sibling and makes the formaldehyde point explicit. Formaldehyde is banned outright as a cosmetic ingredient in the EU and UK, having been classified a Category 1B carcinogen; the releasers that can produce it, imidazolidinyl urea among them (Annex V, entry 27), remain permitted. Regulatory — UK SAG-CS Opinion 2022; Cosmetic Regulation 1223/2009 Products that release formaldehyde above a threshold must say "contains formaldehyde," and regulators are tightening that threshold from 0.05% to 0.001% (10 ppm) specifically to protect formaldehyde-allergic consumers. Regulatory — UK SAG-CS Opinion 2022 The aim is disclosure for the sensitized, not removal of a low-risk preservative.
What the research says
- A formaldehyde releaser, not a carcinogen itself. Slowly liberates formaldehyde (IARC 1) as its preserving mechanism. Peer-reviewed — de Groot et al. 2010
- The weakest common releaser. Lowest patch-test prevalence (1.20%) of the five; releases less formaldehyde than diazolidinyl urea. Peer-reviewed — Karimian et al. 2026
- Cross-reacts with diazolidinyl urea. Shared decomposition products mean co-sensitization; avoid both if allergic to one. Peer-reviewed — Karimian et al. 2026
- Regulated by disclosure. Formaldehyde banned as an ingredient; releasers permitted but labelled; threshold tightening to 0.001%. Regulatory — UK SAG-CS 2022
What helps reduce it
Read labels if you are sensitized. "Imidazolidinyl urea" is named on ingredient lists, with a "contains formaldehyde" warning above the threshold. Regulatory — UK SAG-CS 2022
Avoid the whole releaser group if allergic. Because of cross-reactivity, formaldehyde-allergic people should steer clear of leave-on products preserved with any releaser. Peer-reviewed — de Groot et al. 2010
Launder bedding normally. The residue washes out; formaldehyde is water-soluble and volatile. Inferred
What does NOT help
- Fearing it as a carcinogen. The urea is not classified as carcinogenic; the trace formaldehyde it releases is the issue, and the practical concern is allergy, not cancer from cosmetic use. Peer-reviewed — de Groot et al. 2010
- Switching to diazolidinyl urea to "be safe." That is the stronger releaser and they cross-react — no benefit for a sensitized person. Peer-reviewed — Karimian et al. 2026
Open research questions
- The real-world contribution of bedding-transferred formaldehyde to dermatitis in sensitized sleepers. Speculation
- Whether the lower 0.001% labelling threshold meaningfully reduces flares for the formaldehyde-allergic. Speculation
Citations
- de Groot AC, et al. (2010). Formaldehyde-releasers in cosmetics: relationship to formaldehyde contact allergy. Contact Dermatitis. ~20% of US cosmetics contain a releaser; releasers can exceed 200 ppm formaldehyde; advise formaldehyde-allergic patients to avoid leave-on products with quaternium-15, diazolidinyl urea, DMDM hydantoin or imidazolidinyl urea. Via Consensus. Reference record Peer-reviewed
- Karimian K, et al. (2026). The prevalence of contact allergy to formaldehyde and formaldehyde releasers: a systematic review and meta-analysis. Contact Dermatitis. Imidazolidinyl urea pooled prevalence 1.20% — lowest of the five releasers; diazolidinyl urea 1.42%, quaternium-15 1.89%; geographic differences support EU regulation's effectiveness. 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); imidazolidinyl urea permitted (Annex V entry 27); "contains formaldehyde" label above 0.05%, recommended lowered to 0.001%. UK OPSS / SAG-CS Regulatory
Frequently asked questions
Is imidazolidinyl urea a carcinogen?
No — the urea itself is not a classified carcinogen. It is a formaldehyde releaser: it slowly decomposes in a product to give off small amounts of formaldehyde, which is the preserving action, and formaldehyde is the IARC Group 1 carcinogen. The honest description is a formaldehyde donor, not a carcinogen in its own right. Of the common urea releasers, imidazolidinyl urea is among the least formaldehyde-active, releasing less than its sibling diazolidinyl urea.
How is it different from diazolidinyl urea?
They are close relatives — imidazolidinyl urea is sold as Germall 115, diazolidinyl urea as Germall II — and they cross-react, meaning someone allergic to one often reacts to the other because they share decomposition products. The practical difference is strength: imidazolidinyl urea releases less formaldehyde and is the milder, less allergenic of the two, with the lowest patch-test prevalence of the five common releasers.
Why does it matter in the bedroom?
Like the other personal-care preservatives, it arrives on your bed as a residue from products applied before sleep — lotions, creams, shampoos — that transfer onto sheets and pillowcases. For most people this is of no consequence. It matters to the minority allergic to formaldehyde or to the urea itself, for whom leave-on residues can trigger or maintain contact dermatitis, frequently on the face.
Should I avoid it?
Only if you are sensitized. Imidazolidinyl urea is the weakest of the common formaldehyde releasers — positive in about 1.2% of patch-tested dermatitis patients — so it is not a general concern. If you have a formaldehyde or formaldehyde-releaser allergy, avoid leave-on products preserved with it; it is named on the label, and a 'contains formaldehyde' warning appears above a set threshold. Formaldehyde-free options are easy to find.
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.