Formaldehyde releasers: why to avoid them and what to use instead
These preservatives slowly release formaldehyde, a known human carcinogen and a common contact allergen, into the product over its shelf life.
The short answer
Quaternium-15 and DMDM hydantoin are the two most common and the two most frequently implicated in allergic contact dermatitis. Salon keratin treatments are the highest-exposure scenario by a wide margin.
- Where it hides
- Shampoo, conditioner, body wash, keratin treatments, nail hardener, some baby products
- Cleaner swap
- Sodium benzoate with potassium sorbate, phenoxyethanol, benzyl alcohol, or waterless bar formats that need no preservative.
- Also listed as
- DMDM hydantoin, Quaternium-15, Imidazolidinyl urea, Diazolidinyl urea, Bronopol, Sodium hydroxymethylglycinate
The label names to scan for
- DMDM hydantoin
- Quaternium-15
- Imidazolidinyl urea
- Diazolidinyl urea
- Bronopol (2-bromo-2-nitropropane-1,3-diol)
- Sodium hydroxymethylglycinate
- Methenamine
- 5-bromo-5-nitro-1,3-dioxane
What regulators have actually done
The EU requires a 'releases formaldehyde' warning above 0.001% and has banned several releasers outright. California's Proposition 65 lists formaldehyde as a carcinogen; the FDA has proposed banning formaldehyde in hair-smoothing products.
Why a releaser instead of formaldehyde itself
Free formaldehyde is unstable and heavily regulated, so formulators use compounds that hydrolyse and release small amounts continuously. That keeps the product preserved for years but means low-level formaldehyde exposure every time you use it.
The salon exposure case
Brazilian blowout-style keratin treatments heat the product to well above room temperature, converting releasers into airborne formaldehyde in a confined space. Occupational monitoring has repeatedly found levels exceeding workplace limits for stylists — the strongest argument for avoidance in this category.
Formaldehyde releasers: frequently asked questions
What is DMDM hydantoin?+
A preservative that slowly releases formaldehyde to keep water-based cosmetics free of bacteria and mould. It appears most often in shampoo and conditioner.
Can formaldehyde releasers cause allergies?+
Yes. They are among the more frequent causes of allergic contact dermatitis in patch-test clinics, and someone allergic to formaldehyde will usually react to all releasers.