Formaldehyde
IARC Group 1 human carcinogen. Avoided in pregnancy due to miscarriage risk in occupational exposure studies. Common in hair-straightening treatments.
Quick answer
Avoid formaldehyde during pregnancy. IARC Group 1 human carcinogen. Inhalation and dermal exposure are linked to increased miscarriage risk in salon-worker studies — particularly relevant for keratin/Brazilian hair-straightening treatments. Choose formaldehyde-free alternatives.
INCI name
Formaldehyde
CAS number
50-00-0
Also known as
Methanal, methylene oxide, formalin (aqueous solution)
Formula
CH2O
What is Formaldehyde?
What formaldehyde is
Formaldehyde is the simplest aldehyde — a colorless gas at room temperature, soluble in water (formalin). It’s used industrially as a disinfectant, preservative, and chemical building block. In personal care products it appears either as free formaldehyde (rare in modern formulations) or via “formaldehyde donors” that slowly release it (covered separately under DMDM Hydantoin)1.
Why formaldehyde is avoided in pregnancy
Formaldehyde is classified as a Group 1 human carcinogen by the International Agency for Research on Cancer (IARC) — the highest category. The classification is based on epidemiological evidence linking inhalation exposure to nasopharyngeal cancer and myeloid leukemia2.
For pregnancy specifically, occupational studies have shown:
- Increased miscarriage risk in salon workers, embalmers, and lab technicians with chronic formaldehyde exposure3
- Possible association with low birth weight and preterm birth in higher-exposure populations
- Particularly relevant for keratin/Brazilian hair-straightening treatments, which can release significant formaldehyde during heat application
Where formaldehyde shows up
In personal care and household products:
- Keratin/Brazilian hair-straightening treatments — the highest-exposure scenario. Even “formaldehyde-free” products often contain methylene glycol or related compounds that release formaldehyde under heat4.
- Some nail polishes and nail hardeners
- Particle board and pressed-wood furniture (off-gassing)
- Cigarette smoke (passive exposure)
- Some embalming-fluid-adjacent products
For cosmetics, the larger concern is formaldehyde-releasing preservatives (DMDM hydantoin, imidazolidinyl urea, quaternium-15) which slowly release formaldehyde over the product’s shelf life. See the dedicated DMDM Hydantoin page.
If you work in a salon or with formaldehyde
Discuss with your OB. Many salon professionals modify their practice during pregnancy: avoiding keratin treatments, improving ventilation, wearing N95 respirators when working with formaldehyde-containing products. Employer accommodations may be appropriate3.
Safer alternatives
For hair smoothing without formaldehyde: amino-acid based smoothing treatments, glyoxylic acid treatments (a newer alternative), and traditional silicone-based serums are formaldehyde-free options.
Is Formaldehyde safe while breastfeeding?
Continue to avoid formaldehyde occupational exposure during breastfeeding.
When to talk to your OB
If you used a product containing Formaldehyde before learning you were pregnant, mention it at your next prenatal visit — but most topical cosmetic exposures are not a cause for panic. For prescription exposures or specific concerns, contact your OB or midwife directly.
Sources
- U.S. National Library of Medicine. Formaldehyde. PubChem. View source →
- International Agency for Research on Cancer. (2012). Formaldehyde, 2-butoxyethanol and 1-tert-butoxypropan-2-ol. IARC Monographs Volume 88. View source →
- Pierce JS, Abelmann A, Spicer LJ, et al. (2011). Characterization of formaldehyde exposure resulting from the use of four professional hair straightening products. Journal of Occupational and Environmental Hygiene. View source →
- U.S. Occupational Safety and Health Administration. Hair Smoothing Products That Could Release Formaldehyde. OSHA Hazard Alert. View source →