Formaldehyde
Banned in EU cosmetics or credibly linked to serious harm.
Also written as: Methanal · Formalin · Methylene Oxide
What it is
Formaldehyde is a small, highly reactive gas usually supplied dissolved in water. It was once a mainstream cosmetic preservative and nail hardener. It carries a harmonised EU classification as a category 1B carcinogen, and IARC classifies it as carcinogenic to humans on the basis of inhalation exposure. It was removed from the EU list of permitted cosmetic preservatives and prohibited outright in 2019.
Worth knowing
Classified as a carcinogen
The carcinogenic evidence relates to inhaled formaldehyde (nasopharyngeal cancer and leukaemia in occupational settings) rather than to skin contact with a cosmetic. That distinction matters, but the classification is why it is banned outright rather than merely limited.
Matters most toEveryone; it should not be present in any EU cosmetic.
A common and clinically important contact allergen
A 2026 systematic review of 158 studies covering 1,347,638 dermatitis patients found a pooled formaldehyde contact allergy prevalence of 2.88%, clinically relevant in about 42% of positive cases.
Matters most toPeople with eczema or dermatitis of unknown cause; they should also avoid formaldehyde-releasing preservatives.
Can still appear indirectly through releasers
Because DMDM hydantoin, diazolidinyl urea and imidazolidinyl urea remain permitted, small amounts of free formaldehyde can still be present. That is why the EU requires a 'releases formaldehyde' warning above 10 ppm.
Matters most toPeople with confirmed formaldehyde allergy.
Where the EU stands
Banned in EU cosmetics
Prohibited as a cosmetic ingredient in the EU since 2019. It was deleted from Annex V (former entry 5) and is listed among the substances prohibited in cosmetic products in Annex II. Separately, products containing formaldehyde-releasing preservatives must be labelled 'releases formaldehyde' where free formaldehyde exceeds 0.001% (10 ppm).
Regulation (EC) No 1223/2009, Annex II (prohibited substances); deleted from Annex V by Commission Regulation (EU) 2019/831; labelling rule from Commission Regulation (EU) 2022/1181 · source ↗
Sources (2)
Every link goes to the original: a journal, a PubMed record or an EU document.
- [1]The Prevalence of Contact Allergy to Formaldehyde and Formaldehyde Releasers: A Systematic Review and Meta-Analysis
Contact Dermatitis · 2026 · doi:10.1111/cod.70172
Pooled prevalence of formaldehyde contact allergy was 2.88% across 1.35 million patients, clinically relevant in 41.6% of positives; the paper confirms formaldehyde has been prohibited as a direct EU cosmetic ingredient since 2019.
- [2]Contact dermatitis associated with preservatives: Retrospective analysis of North American Contact Dermatitis Group data, 1994 through 2016
Journal of the American Academy of Dermatology · 2021 · doi:10.1016/j.jaad.2020.07.059
Formaldehyde produced positive patch tests in 7.8% of 50,799 patients, making it one of the leading preservative allergens in the series.