High concernPreservative
DMDM Hydantoin
Formaldehyde releaserKnown carcinogenAllergenSkin irritant
What it is
A hydantoin-based preservative that slowly releases formaldehyde as it breaks down in aqueous solutions.
What it does
Preserves water-based products against bacterial and fungal growth in shampoos, conditioners, lotions, and sunscreens.
Why it’s a concern
Formaldehyde is classified by IARC as a Group 1 human carcinogen (causally linked to nasopharyngeal cancer and leukaemia). While DMDM hydantoin releases only small amounts over time, the continuous low-level exposure is a concern for scalp and skin contact. A 2021 class-action lawsuit against a major haircare brand cited DMDM hydantoin as a cause of hair loss and scalp irritation. Contact dermatitis rates among dermatology clinic patients are well documented.
Also known as
1,3-dimethylol-5,5-dimethylhydantoin
CAS numbers
6440-58-0
Commonly found in
shampooconditionerlotionsunscreen
Safer alternatives
- sodium benzoate
- potassium sorbate
- leucidal liquid
- glyceryl caprylate
Related chemical families
Sources
- IARC Monograph Volume 100F
- American Contact Dermatitis Society Allergen of the Year 2015 (formaldehyde)