Dmdm Hydantoin
Also known as Dimethyloldimethyl hydantoin, 1,3-Bis(hydroxymethyl)-5,5-dimethylimidazolidine-2,4-dione, Glydant
“CIR Expert Panel says: safe as used in cosmetics.”
DMDM Hydantoin is a widely studied formaldehyde-releasing preservative with a CIR unqualified Safe (S) finding from a 1988 assessment confirmed in 2005 (JACT 7(3):245-77). The primary safety concern is the slow release of formaldehyde in aqueous formulations, which can trigger reactions in formaldehyde-allergic individuals. de Groot et al. (2010) documented sensitization frequencies to formaldehyde-releasers in European patch-test populations at 0.3–1.4% depending on the specific compound, with DMDM Hydantoin showing a direct relationship between positive patch tests and prior formaldehyde allergy. Lv et al. (2015) quantified release rates across eight preservatives, finding DMDM Hydantoin in the mid-range, with release dependent on matrix, pH, time, and temperature. A 2023 quantitative risk assessment (PMID 37177794) found the margin of safety for a shampoo containing 1% DMDM Hydantoin was above 1 for typical use scenarios in healthy individuals, indicating low induction risk.
Broad-spectrum antimicrobial preservative effective against bacteria, yeasts, and molds
Widely used in rinse-off products (shampoos, conditioners) where short contact time limits exposure
CIR Expert Panel found it safe in cosmetic use at the concentrations studied (1988, reconfirmed 2005)
Mid-range formaldehyde releaser — releases less than paraformaldehyde and diazolidinyl urea at equivalent concentrations
- · Formaldehyde releaser: hydrolyzes in aqueous formulations to release free formaldehyde, which is a known contact allergen and Category 1B skin sensitizer
- · Patients with pre-existing formaldehyde allergy can develop allergic contact dermatitis from DMDM Hydantoin-containing cosmetics (cross-reactivity mechanism)
- · Patch test data shows direct correlation between DMDM Hydantoin reactivity and formaldehyde allergy
- · Formaldehyde is classified as a human carcinogen (IARC Group 1) at high inhalation exposures; dermal exposure from rinse-off cosmetics is considered lower risk
EU Annex V (Entry 33) restricts max concentration to 0.6% with mandatory warning label if released formaldehyde exceeds 0.05% (pre-2026 threshold); EU is tightening the warning threshold to >0.001% formaldehyde effective July 2026
CIR Quick Reference Table (12/2017, revised 07/2018) — DMDM Hydantoin row: Finding=S, Citation=JACT 7(3):245-77, 1988 confirmed 09/05
“DMDM Hydantoin | S | [no Detail entry] | JACT 7(3):245-77, 1988 confirmed 09/05”— QRT-122017revised072018.pdf, p. 41