Ingredient Guide
Formaldehyde & Formaldehyde Releasers in Beauty Products
Formaldehyde is a known human carcinogen. It appears directly in some nail and hair products — and is released over time by a family of preservatives used across many product categories. Here's what beauty professionals need to know.
Why formaldehyde matters in a salon setting
Formaldehyde is classified as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC). In beauty settings, cumulative occupational exposure comes from: direct formaldehyde in nail hardeners and some smoothing treatments; formaldehyde released by preservatives in shampoos and treatments; and formaldehyde produced when heat is applied to certain smoothing treatment ingredients.
A single exposure is low-risk. The concern for beauty professionals is repeated daily exposure across multiple clients — inhalation, skin contact, and eye irritation accumulating over a career. Proper ventilation, nitrile gloves, and ingredient awareness are the primary protective measures.
Formaldehyde-releasing preservatives (full list)
DMDM Hydantoin
HighFound in: Shampoos, conditioners, lotions, hair treatments
recognized skin sensitizer, significant formaldehyde releaser
Quaternium-15
HighFound in: Shampoos, cosmetics, nail hardeners
one of the strongest formaldehyde releasers in cosmetics
Imidazolidinyl urea
ModerateFound in: Shampoos, moisturizers, hair products
slower releaser, but cumulative with other releasers
Diazolidinyl urea
ModerateFound in: Shampoos, skin care, hair products
releases at a higher rate than imidazolidinyl urea
2-Bromo-2-nitropropane-1,3-diol (Bronopol)
ModerateFound in: Shampoos, lotions
low formaldehyde release but independently sensitizing
Sodium hydroxymethylglycinate
Low-moderateFound in: Moisturizers, hair products
releases small amounts of formaldehyde
Tosylamide/formaldehyde resin
ModerateFound in: Nail polish, nail hardeners
film-former; can cause nail allergies in sensitized individuals
Glyoxylic acid
High when heatedFound in: 'Formaldehyde-free' smoothing treatments
produces formaldehyde-like compounds under flat iron heat
Methylene glycol
HighFound in: Brazilian blowout products
legally classified as formaldehyde in aqueous solution by FDA/OSHA
Frequently asked questions
- What is DMDM hydantoin and does it release formaldehyde?
- DMDM hydantoin is a preservative that slowly releases formaldehyde to prevent microbial growth in cosmetic products. It is considered a formaldehyde releaser and is found in shampoos, conditioners, hair treatments, and lotions. It is a recognized skin sensitizer and contributes to cumulative formaldehyde exposure in professional settings.
- Are formaldehyde-free keratin treatments actually formaldehyde-free?
- Not always. Many products marketed as formaldehyde-free contain glyoxylic acid, methylene glycol, glutaraldehyde, or DMDM hydantoin — ingredients that release or behave similarly to formaldehyde when heated. California, the EU, and several other jurisdictions regulate or restrict these even when labeled as formaldehyde alternatives.
- Which nail products contain formaldehyde or releasers?
- Formaldehyde is used directly as a nail hardener (typically listed as Formalin or formaldehyde). Formaldehyde releasers including DMDM hydantoin, Quaternium-15, tosylamide/formaldehyde resin, and imidazolidinyl urea appear in nail hardeners and strengtheners. Tosylamide/formaldehyde resin is a film-forming agent in many nail polishes.
Check for formaldehyde releasers in your products
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