Ingredient dictionary

DMDM Hydantoin

DMDM hydantoin is a preservative that slowly releases small amounts of formaldehyde to stop bacteria and mold from growing in a product. It is on the label of 6 products in our library. Checked against our library November 6, 2026.

The catch: it belongs to the formaldehyde releaser family, so people with a formaldehyde allergy are generally told to avoid it, since it slowly gives off formaldehyde.

Formaldehyde releasers. People with a formaldehyde allergy are told to avoid these preservatives too.

What DMDM Hydantoin does

Keeps bacteria and mold from growing
Protects water-based formulas from spoiling
Helps products stay fresh on the shelf

DMDM hydantoin is made by reacting a hydantoin base with formaldehyde, which gives a compound that holds onto formaldehyde and releases it slowly. Formulators like it for rinse-off products such as shampoos and cleansers, because it works well in water-based formulas and helps them last on the shelf.

In a finished product, it is rarely noticed by feel or scent. It is used in small amounts, so it adds little to the texture of a shampoo or cleanser. Its job is quiet: it keeps the formula stable between uses, which matters most for products that are opened and used often.

Good for

Rinse-off products like shampoos and cleansers, where a preservative keeps water-based formulas stable.

Be careful if

It belongs to the formaldehyde releaser family, so people with a formaldehyde allergy are generally told to avoid it, since it slowly gives off formaldehyde.

Frequently asked questions

Is DMDM hydantoin safe?

It is permitted in cosmetics in many countries, and most people use products containing it without trouble. The main concern is for people with a formaldehyde allergy, who are usually advised to avoid formaldehyde releasers. If you have sensitive skin or a known allergy, ask a dermatologist.

Does DMDM hydantoin release formaldehyde?

Yes. It is a formaldehyde releaser, so it slowly gives off small amounts of formaldehyde. That slow release is how it keeps water-based products from growing bacteria and mold.