Formaldehyde-releasing preservatives, explained

What the term means

We work from documents and have not tested any products. This page sets out what a few public sources say about one family of cosmetic preservatives, and where those sources stop.

Preservatives are added to water-containing products to keep them from spoiling. Formaldehyde releasers are preservatives that give off formaldehyde. A 2009 review in Contact Dermatitis (PMID 19706047) identified 35 chemicals as formaldehyde releasers, and listed seven more that the literature calls releasers but for which data are “inadequate to consider them as such beyond doubt.” It also notes “nomenclature mistakes and outdated information” in the field, so lists of releasers vary.

PubChem (retrieved 2026-11-14) describes one of them, DMDM hydantoin, as “an antimicrobial formaldehyde releaser preservative with the trade name Glydant,” belonging to a class called hydantoins, “used in the cosmetics industry and found in products like shampoos, hair conditioners and skin care products.”

The names on a label

The EU’s glossary of common ingredient names, Commission Decision (EU) 2019/701, is the official list used for cosmetic ingredient labelling in the EU. We checked each name below against its text (retrieved 2026-11-14). These are the entries it contains:

Substance	Glossary entry	Entry number
DMDM hydantoin	DMDM HYDANTOIN	8286
Quaternium-15	QUATERNIUM-15	20965
Diazolidinyl urea	DIAZOLIDINYL UREA	7197
Imidazolidinyl urea	IMIDAZOLIDINYL UREA	11750
Formaldehyde	FORMALDEHYDE	9245
2-Bromo-2-nitropropane-1,3-diol	2-BROMO-2-NITROPROPANE-1,3-DIOL	191

An exact search for the one-word form “BROMONITROPROPANEDIOL” found no entry, so we do not give it as a label name. PubChem lists other names for DMDM hydantoin, among them Glydant and 1,3-Dimethylol-5,5-dimethylhydantoin, with CAS number 6440-58-0, but does not say which appear on labels. Our guide to reading an ingredient list and our page on allergen names on ingredient labels cover label wording for fragrance.

The glossary tells you the official name of an ingredient. It says nothing about whether a releaser is present at a level that matters, which the next sections take up.

Why researchers study them

The 2026 abstract opens by calling formaldehyde and its releasers “common preservatives and potent sensitizers.” Contact allergy, in the words of the EU’s fragrance-allergen regulation text that we read for our guide to the 26 fragrance allergens, is a lasting change in the immune system, and eczema can develop on re-exposure. The preservative question is the same kind of problem as fragrance allergy, but the substances are different.

How common is the allergy

A 2026 systematic review and meta-analysis (PMID 42035787, Contact Dermatitis) searched PubMed, Embase and Web of Science up to 30 September 2025 and included 158 studies covering 1,347,638 dermatitis patients. It reports pooled prevalence of contact allergy among those patients of:

• formaldehyde, 2.88% (95% CI 2.55-3.24), with clinical relevance of 41.57%
• 2-bromo-2-nitropropane-1,3-diol, 2.76%
• quaternium-15, 1.89%, with the highest clinical relevance of the group at 55.67%
• diazolidinyl urea, 1.42%
• DMDM hydantoin, 1.37%
• imidazolidinyl urea, 1.20%

The abstract reports prevalence of 2.96% among children and 2.61% among adults, with no significant difference, and 2.65% against 2.85% for patients with and without atopic dermatitis, again with no significant difference. It reports the highest regional prevalence in North America (6.8%) and says the disparities “suggest that regulatory interventions, such as the EU’s prohibition of formaldehyde and quaternium-15 in cosmetics, are highly effective public health measures.” We did not read the underlying EU legal text, so we repeat this only as the authors’ statement.

These figures describe people who were already referred for patch testing because of dermatitis, so they do not give the chance that an ordinary user will react.

The 2009 review adds that formaldehyde allergy frequency is consistently higher in the USA (8-9%) than in Europe (2-3%), and warns that patch testing with a 1% formaldehyde solution “may result in both false-positive and false-negative (up to 40%) reactions” and that judging whether a positive result is relevant is “often challenging.”

How the releaser and the formaldehyde allergy connect

The 2010 review (PMID 20136876) reports that “15% of all reactions to 2-bromo-2-nitropropane-1,3-diol and 40-60% of the reactions to the other releasers are caused by a reaction to the formaldehyde in the test material.” So for most releasers, a good share of positive patch tests reflect an underlying formaldehyde allergy.

A Finnish occupational-clinic study (PMID 18976378, 2008) patch tested 81 patients with formaldehyde allergy and 18 with allergy to some releaser independent of formaldehyde between 2001 and 2007. It found reactions to releasers in 79% of the formaldehyde-allergic patients and said allergy to a releaser without formaldehyde allergy was rare compared with studies on general dermatological patients. Sources of sensitisation included metalworking fluids first, then creams, and the authors said exposure to releasers in liquid soaps and other rinse-off products was common.

How much formaldehyde is in a product

This is where the sources are most cautious. The 2010 review says there is only “fragmented data” on free formaldehyde in cosmetics preserved with these donors. It states that all the releasers it examined except 2-bromo-2-nitropropane-1,3-diol (for which data are lacking) “can, in the right circumstances of concentration and product composition, release >200 p.p.m. formaldehyde, which may result in allergic contact dermatitis.” It then says: “Whether this is actually the case in any particular product cannot be determined from the ingredient labelling.”

The 2009 review says levels of 200-300 p.p.m. free formaldehyde in cosmetic products have been shown to induce dermatitis from short-term use on normal skin, and that “what concentration of formaldehyde is safe for sensitive patients remains unknown.”

Based on this, the 2010 authors recommended advising patients allergic to formaldehyde “to avoid leave-on cosmetics preserved with quaternium-15, diazolidinyl urea, DMDM hydantoin, or imidazolidinyl urea, acknowledging that many would tolerate some products.” That recommendation is addressed to clinicians about patients with a diagnosed allergy. We report it and do not extend it to anyone else.

What this means for a fragrance-free shopper

These are preservatives. A fragrance-free test, ours included, looks for fragrance, parfum, aroma, perfume, essential oils and fragrance chemicals in the maker’s published ingredient list. It does not screen for preservatives, so a product can pass it and still list a formaldehyde releaser. See fragrance-free vs unscented and what parfum means for the fragrance side, and what hypoallergenic means for why that label is not a screen for specific ingredients.

Preservatives are discussed on their own pages here: phenoxyethanol, parabens, methylisothiazolinone and sodium benzoate. Category pages where preservative choice shows up in ingredient lists include fragrance-free skincare, shampoo and baby wash. The broader fragrance-free products guide explains how we read maker ingredient lists.

A plain line

This page reports what published sources say. It is not advice on any individual’s skin. For a suspected reaction, or if you have been told you are allergic to formaldehyde, ask a dermatologist or an allergy or dermatology society.

What we don’t fully know

Our unknowns section lists the limits. In short: we read four abstracts and one database record, no regulator text on these substances, and no data on any named product, and the sources do not say what level is acceptable for people who are already sensitised.