Keratin itself does not cause cancer. It is a natural protein that makes up your hair, skin, and nails. But “keratin treatments” sold in salons often contain formaldehyde, a chemical classified as a known human carcinogen. The confusion comes from the product name borrowing a harmless protein’s reputation to market what is essentially a chemical straightening process.
Keratin the Protein vs. Keratin the Treatment
Keratin is one of the most abundant proteins in your body. It forms the structural framework of your skin cells, giving them mechanical strength and integrity. A slightly different version of the protein, with a higher sulfur content that allows for tighter cross-linking, builds the hard tissue in your hair and nails. This protein is completely harmless. Your body produces it constantly.
What salons call a “keratin treatment” or “Brazilian blowout” is a smoothing process that coats hair strands with a liquid solution, then seals it with a flat iron at temperatures often exceeding 150 to 200°C. The smoothing effect comes not from keratin but from chemicals in that solution, and the most effective (and most common) active ingredient is formaldehyde or a compound that releases formaldehyde when heated.
Why Formaldehyde Is the Real Concern
The International Agency for Research on Cancer classifies formaldehyde as a Group 1 carcinogen, its highest category. There is sufficient evidence linking formaldehyde exposure to nasopharyngeal cancer (cancer in the upper throat behind the nose) and to leukemia. There is also limited evidence connecting it to cancers of the nasal cavity and sinuses.
When a stylist applies a keratin smoothing product and then heats it with a blow dryer or flat iron, formaldehyde gas is released into the air. Both the stylist and the client breathe it in. The FDA has confirmed this happens even with products labeled “formaldehyde-free,” because many contain related chemicals like methylene glycol or formalin, which are simply other names for formaldehyde or compounds that convert to it under heat.
Products Labeled “Formaldehyde-Free” Aren’t Always Safe
Testing has repeatedly shown that products marketed as formaldehyde-free still release formaldehyde into salon air when heated. The FDA warns consumers to check ingredient lists for three terms: formaldehyde, formalin, and methylene glycol. If any of these appear, the product contains or releases formaldehyde regardless of what the front label says.
Some newer products use glyoxylic acid or glycolic acid as alternatives. These do avoid intentionally adding formaldehyde, but they come with their own problems. Research published in the World Journal of Nephrology found that glyoxylic acid can also release formaldehyde when exposed to flat-iron temperatures. Beyond that, these products have been linked to acute kidney injury. A systematic review documented cases where oxalate crystals deposited in kidney tissue after exposure. In 77% of cases where biopsies were performed, oxalate crystals were found in the kidney tubules. Most patients experienced nausea and vomiting. While most recovered, some cases were severe enough to involve breathing difficulty, dangerous blood pressure spikes, or dangerously high potassium levels.
Who Faces the Greatest Risk
Stylists face far more exposure than clients. A client sits through one treatment lasting a couple of hours, perhaps a few times a year. A stylist may perform these treatments multiple times a week for years, breathing in formaldehyde gas each time. The CDC has flagged keratin hair-smoothing treatments as a specific occupational hazard, warning that stylists are at risk for exposure to a known asthmagen (a substance that causes or worsens asthma) and carcinogen.
OSHA sets workplace limits at 0.75 parts per million over an eight-hour shift and 2 ppm during any 15-minute period. When salon air exceeds those levels, owners are required to install ventilation systems, use lower heat settings on dryers and flat irons, and provide respirators to workers at no cost. In practice, many salons lack adequate ventilation, and many stylists are unaware of the chemical exposure involved.
A large NIH-supported study also found that women who used chemical hair straightening products frequently had a higher risk of uterine cancer. The researchers noted that several chemicals found in straighteners, including formaldehyde, parabens, bisphenol A, and metals, could be contributing to that elevated risk.
How to Reduce Your Exposure
If you are considering a keratin treatment, your risk depends on the specific product used and how often you get it done. A single treatment in a well-ventilated salon poses a much lower risk than repeated treatments in a poorly ventilated space. Still, there are practical steps you can take to minimize exposure.
- Ask for the ingredient list. Look for formaldehyde, formalin, or methylene glycol. If any appear, the product releases formaldehyde when heated.
- Don’t trust “formaldehyde-free” labels alone. Independent testing has repeatedly found formaldehyde in products making this claim. Ask the stylist what specific active ingredient the product uses.
- Check ventilation. The treatment should be done in a room with open windows, exhaust fans, or a dedicated ventilation system. If you can smell a sharp, irritating chemical odor during the process, formaldehyde is likely present in the air.
- Consider frequency. Occasional use carries lower cumulative risk than treatments every few months over many years.
Regulatory Action Is Still Pending
The FDA has proposed a rule that would ban formaldehyde and formaldehyde-releasing chemicals as ingredients in hair smoothing and straightening products sold in the United States. As of the most recent regulatory timeline, a formal proposed rule was expected in late 2024, but the ban has not yet taken effect. Until it does, these products remain legally available, and the burden of identifying and avoiding them falls on consumers and stylists.