Reference summary — not medical advice or a personal risk estimate.
Hair straightening / relaxer
Chemical treatments to straighten hair. Formaldehyde-releasing formulations are the highest-risk category.
Also known as: keratin treatment, chemical straightener
What this does NOT mean
Finding a factor documented in this product category does not establish that ordinary use of hair straightening / relaxer causes cancer. It means research — through regulatory testing, recall records, or IARC review — has found that chemical present in this category. Whether it matters for you depends on formulation, dose, frequency, and route of exposure.
What has been documented
- FormaldehydeIARC Group 1IARC Group 1Contains · high confidence
Some keratin and chemical smoothing treatments release formaldehyde during application, especially when heated. FDA has issued warnings and OSHA has issued a hazard alert.
Evidence source: US FDA
How to read this page
A factor appearing on this page means it has been documented in this product category — through EPA / FDA testing, IARC monographs, or regulatory recall records. Whether it presents a meaningful personal risk depends on the specific formulation, dose, and how you're exposed. Click any factor to read what science actually says about it, and where.