DMDM Hydantoin
Description
DMDM Hydantoin is a synthetic compound belonging to the hydantoin family. In cosmetics it is commonly found in shampoos, conditioners, cleansers, creams, lotions and other water-containing formulations.
It belongs to the group of formaldehyde releasers, substances capable of gradually releasing small amounts of formaldehyde within a formulation. This property accounts both for its antimicrobial effectiveness and for the main toxicological and dermatological concern associated with the ingredient.
Identification data and specifications
| Item | Data |
|---|---|
| INCI | DMDM Hydantoin |
| Chemical name | 1,3-Bis(hydroxymethyl)-5,5-dimethylimidazolidine-2,4-dione |
| CAS | 6440-58-0 |
| EC | 229-222-8 |
| Molecular formula | C₇H₁₂N₂O₄ |
| Molecular weight | 188.18 g/mol |
| Category | Preservative; formaldehyde releaser |
Technical and regulatory data
| Property | Data |
|---|---|
| Appearance | Solid/powder; also commercially available as aqueous solutions |
| Odour | Odourless |
| Water solubility | High, approximately 77.3 g/100 ml |
| Common cosmetic applications | Shampoos, conditioners, cleansers, creams, lotions and hair products |
| European Union | Cosmetics Regulation, Annex V/33 |
| Maximum EU concentration | 0.6% |
| Released-formaldehyde warning | Required when total released formaldehyde in the finished product exceeds 0.001% (10 ppm) |
Safety and sensitisation
The main concern associated with DMDM Hydantoin is skin sensitisation. Formaldehyde is a well-established contact allergen, and formaldehyde released from DMDM Hydantoin may cause or trigger allergic contact dermatitis, particularly in previously sensitised individuals.
A large systematic review and meta-analysis published in 2026, including 158 studies and more than 1.3 million dermatitis patients, reported a pooled prevalence of positive reactions to DMDM Hydantoin of 1.37%. This figure refers to dermatitis patients undergoing patch testing and must not be interpreted as the prevalence of allergy in the general population.
Sensitivity to DMDM Hydantoin is also closely associated with previous sensitisation to formaldehyde. Individuals with a known allergy to formaldehyde or other formaldehyde-releasing preservatives should therefore exercise particular caution and may benefit from avoiding products containing it.
A quantitative risk assessment published in 2023 on shampoo use nevertheless concluded that, under the exposure conditions modelled, the risk of inducing new sensitisation in previously non-sensitised consumers was low. This finding does not remove the concern for individuals already allergic to formaldehyde and does not contradict documented cases of allergic contact dermatitis.
Formaldehyde
Formaldehyde is an irritant and potent sensitiser and has a well-established carcinogenic classification under certain exposure conditions, particularly occupational and inhalation exposure.
However, this does not mean that the presence of DMDM Hydantoin in a cosmetic product at permitted concentrations automatically represents a carcinogenic risk. Risk assessment depends on the amount of formaldehyde actually released, route of exposure, frequency of use and individual susceptibility.
For cosmetic use, the best documented concern therefore remains allergic sensitisation and irritation.
Regulatory status
In the European Union, DMDM Hydantoin is permitted as a preservative at concentrations up to 0.6% under Annex V/33 of Regulation (EC) No 1223/2009.
EU legislation has substantially lowered the labelling threshold for formaldehyde released by preservatives. Where one or more formaldehyde-releasing substances result in more than 0.001% (10 ppm) total released formaldehyde in the finished product, the product must carry the warning “releases formaldehyde”.
The transition period for products complying with the previous threshold ended on 31 July 2026.
In Great Britain, DMDM Hydantoin also remains permitted subject to a maximum concentration of 0.6%.
In the United States, no directly comparable federal concentration limit applies specifically to DMDM Hydantoin in cosmetics. Safety assessments have nevertheless recognised its sensitisation potential and the importance of controlling exposure to released formaldehyde.
Conclusions
DMDM Hydantoin is effective at authorised concentrations, but its ability to release formaldehyde represents a genuine concern, particularly regarding skin sensitisation and allergic contact dermatitis.
Recent scientific evidence confirms the allergenic issue, although the risk of inducing new sensitisation under normal cosmetic-use conditions appears relatively low for most previously non-sensitised consumers.
Particular caution is appropriate for individuals with formaldehyde allergy, contact dermatitis or previous sensitisation to formaldehyde-releasing preservatives.
Classifying the ingredient as critical therefore remains justified under a precautionary approach, provided this is not interpreted as meaning that every cosmetic product containing DMDM Hydantoin necessarily presents a high risk.
