DMDM Hydantoin
DMDM hydantoin is a preservative that prevents microbial growth in products such as shampoos and conditioners by releasing small amounts of formaldehyde over time. Formaldehyde is a strong skin allergen and is classified by IARC as carcinogenic to humans (Group 1). Although the amounts in cosmetics are very low, the high risk range reflects its allergy potential and the availability of safer alternatives.
Risk range
1 is the lowest and 10 the highest risk. The range depends on the amount used, whether the product is rinsed off and how it is used. The Temiz İçerik app uses the same ranges.
At the lower end in rinse-off products and at low levels; it moves towards the upper end in leave-on products, for people with a formaldehyde allergy and in old products or products stored in the heat.
What is DMDM hydantoin and what is it used for?
DMDM hydantoin belongs to a group of preservatives known as formaldehyde releasers. As it comes into contact with water in the product, it gradually releases small amounts of formaldehyde, which kills bacteria and fungi.
Because it is cheap and effective, it was widely used for many years in shampoos, conditioners and liquid soaps. Other substances in the same group include imidazolidinyl urea, diazolidinyl urea, quaternium-15 and sodium hydroxymethylglycinate.
Which products contain it?
- Shampoos, conditioners and hair styling products
- Shower gels and liquid soaps
- Some lotions, make-up and make-up removers
- Some household cleaning products and industrial fluids
Is it harmful? The scientific assessment
What matters is less DMDM hydantoin itself than the formaldehyde it releases. Formaldehyde is one of the known causes of allergic contact dermatitis, and people sensitive to formaldehyde can react with eczema even to the low amounts in products. IARC has classified formaldehyde in Group 1 (carcinogenic to humans); however, this classification is based mainly on high, long-term occupational exposure through inhalation, not on the low skin exposure from cosmetic use.
In the EU, DMDM hydantoin may be used in cosmetics at a maximum of 0.6%. Current EU rules require a “releases formaldehyde” warning on the label of products containing formaldehyde releasers when the amount of formaldehyde released exceeds a certain threshold. This warning is there so that, in particular, people with a formaldehyde allergy can easily identify the product. Turkish legislation is aligned with the EU.
The amount of formaldehyde released can vary with the age of the product, temperature and pH; it can increase in products kept in the heat for a long time. Claims of hair loss have been debated publicly, but no causal link has been established scientifically.
Who should be careful?
- People diagnosed with a formaldehyde allergy: They should look on labels not only for DMDM hydantoin but for all formaldehyde releasers.
- People with recurring eczema on the scalp, face or neck: Having a patch test done by a dermatologist can help find the trigger.
- People choosing products for babies and children: Products without formaldehyde releasers may be preferable.
What to do when you see it on a label
Using a product containing DMDM hydantoin occasionally poses no serious danger if you don't have an allergy. Even so, because there are many alternatives made with preservatives of lower allergy potential, such as phenoxyethanol or methylparaben, choosing these products is a sensible choice, especially for sensitive skin. It also helps to store products in a cool place and pay attention to the expiry date.
Frequently asked questions
Does DMDM hydantoin cause cancer?
DMDM hydantoin itself is not classified as a carcinogen. The formaldehyde it releases is in IARC Group 1, but this assessment is based mainly on high levels of inhaled occupational exposure.
How can I recognise formaldehyde releasers on the label?
The main ones are DMDM Hydantoin, Imidazolidinyl Urea, Diazolidinyl Urea, Quaternium-15 and Sodium Hydroxymethylglycinate. In the EU, products exceeding the threshold also carry a “releases formaldehyde” warning.
Does DMDM hydantoin cause hair loss?
There is no scientifically proven cause-and-effect relationship. If you are experiencing hair loss, you are advised to see a dermatologist.
Sources
Updated: 2026-10-11 · How we score
This page is for general information and is not personal medical advice. Warnings on the product label and the advice of a health professional always come first.