What’s the Deal with Keratin Treatments and Other Hair Straighteners?

Have you ever gotten a keratin treatment? A Brazilian Blowout? Maybe you’ve heard that they make hair silky smooth and relaxed and are expensive. Or maybe you’ve heard that they can cause cancer. Are the risks greater than the benefits?  And what products are the FDA planning to ban in April 2024?

What is a Keratin Treatment?

Keratin is a protein found in the hair, nails, and skin. Keratin affects your hair texture and whether it is straight, wavy, or curly. Using chemicals to change the molecules in coiled or curly hair to make it straight or wavy is known as relaxing the hair. In a keratin treatment, cream containing formaldehyde, or methylene glycol (a chemical that releases formaldehyde when used in hair straightening) is brushed into the hair, which is then blown dry and flat-ironed. The combination of formaldehyde, heat, and compression causes straight keratin in the cream to bind to the keratin in the hair, making curly or wavy hair more relaxed.[1]

Why is Formaldehyde a Problem?

Formaldehyde is a colorless, strong-smelling gas that causes health problems when inhaled, sprayed into the eyes, or absorbed through the skin. It can irritate the eyes, nose, and throat, cause coughing and wheezing, and trigger a severe allergic reaction of the skin, eyes, and respiratory tract.[2] Some people have also reported that it caused headaches, dizziness, nausea, chest pains, vomiting, and rashes. [3] [14] Repeated exposure at high levels has been linked to various cancers, including leukemia, uterine cancer, and ovarian cancer. [4] [5][14] Formaldehyde is released at highly concentrated levels when it is heated, so stylists that perform keratin treatments and customers that repeatedly get them are at a greatest risk for these health problems.[4] That’s why the FDA has been raising alarm as early as 2010 and has plans to ban hair smoothing products with formaldehyde in April 2024.[14][15] 

Which Products and Ingredients are Dangerous?

The New York State Department of Health list the following as some of the companies that sell one or more products that contain formaldehyde: Brazilian Blowout Solution,Cadiveu Brazilian Thermal Reconstruction, Coppola Keratin, QOD GOLD Solution and many more. See the full list of products here. Many of these products have been banned in the E.U. and Canada due to their health risks.[8]

All of these treatments contain either formaldehyde or another chemical that releases formaldehyde when heated. The following chemicals are all considered formaldehyde by OSHA: methylene glycol, formalin, methylene oxide, paraform, formic aldehyde, methanal, oxomethane, oxymethylene, or CAS Number 50-00-0.[6] There are also other hair products, such as conditioners and hair sprays, that contain keratin but do not contain any form of formaldehyde, and do not require heat activation. They just leave keratin on the outside of your hair, rather than binding the molecules together. So, it’s best to read the ingredients label before taking any product home, to make sure that you aren’t exposing yourself to formaldehyde, whether it’s listed as formaldehyde, methylene glycol or by one of these other names.

It’s important to know that Keratin is not the only hair straightener that is dangerous.  A 2022 study indicated a possible link between the use of chemical hair straighteners and uterine cancer. Researchers found women who applied chemical straightening products on their hair at least four or more times a year were more than twice as likely to develop uterine cancer compared to those that did not, and that Black women were at higher risk.  [9] [14]  Following the 2022 NIH study, a lawsuit was filed against L’Oreal and other beauty companies for selling chemical hair straightening products. [10]

Isn’t a Brazilian Blowout “Formaldehyde-Free”? No!

Brazilian Blowout is one of the most common brands of keratin treatments. As a result of the 2010 controversy over formaldehyde in keratin treatments, Brazilian Blowout created a formula that they advertised as “formaldehyde-free.” While there is no formaldehyde listed in the ingredients, the main chemical used is methylene glycol, which releases formaldehyde when it is heated during the treatment process. Because of this, the FDA issued a warning letter to Brazilian Blowout in 2011 saying that the product is “misbranded” because the “formaldehyde-free” label is false or misleading.[11] [15] Brazilian Blowout is actually one of the most dangerous treatments because almost 12% of the product is basically formaldehyde hiding under another name, and contains three times as much formaldehyde as most other keratin treatments.[6] Five other keratin treatments labeled “formaldehyde-free” were also found to contain formaldehyde levels up to five times the recommended amount.[12]

In response to the FDA’s letter, Brazilian Blowout changed the labeling on their original formula to warn consumers about health risks, and created an alternative product called Brazilian Blowout ZERO+, which does not contain any formaldehyde.[15] But according to a company representative, the new product does not leave the hair as smooth as the original.[1]

Risks to Stylists and Customers

Because stylists are at greatest risk for formaldehyde exposure, the national Occupational Safety and Health Administration (OSHA) set a standard for the amount of formaldehyde allowed in the air. [16] If workers have been exposed to more than a specified amount of formaldehyde, their health must be monitored and they must be reassigned to a job with significantly less exposure. The salon is required to install ventilation systems, use lower heat settings on blow dryers, and monitor formaldehyde levels at all times using a Consumer Sampling and Analysis Kit.[3] Other workers should also be trained annually to safely handle chemicals and be provided personal protective equipment, including gloves, aprons, and eyewash stations.[2] Learn more about OSHA’s recommendations for formaldehyde exposure here.

If you are a hairdresser who wants to protect your workers from the health risks of formaldehyde, don’t offer keratin treatments at your salon. If you just thinking of getting regular keratin treatments for yourself (Brazilian Blowout recommends getting treatments every 12 weeks), remember that will put yourself and others at greater risk for irritation, allergic reactions, and even cancer. Regardless, with the FDA’s announcement to ban hair-smoothing products that contain formaldehyde, products that contain or create formaldehyde as an ingredient will not be legally available soon. [14][15]

If you want to straighten your hair, remember that using a flat iron releases water vapor, which is much safer for your health. Of course, any form of straightening will damage hair and should be used sparingly, alternating with protective hairstyles that don’t require altering hair’s natural texture, such as braids or gentle twists. These will give your hair (as well as your skin and sinuses) a break from harsh chemicals and heating elements.

We agree with other experts who say that the FDA should have prohibited the use of formaldehyde in hair straightening products years ago.  The FDA started to do so in 2016, but for reasons that are not clear, that decision was blocked until 2024! [14] We also urge the Federal Trade Commission to crack down on false advertising by products labeled as “formaldehyde-free.”


All articles on our website have been approved by Dr. Diana Zuckerman and other senior staff.

  1. Environmental Working Group. Best options for straight hair, Hair Straighteners. ewg.org. http://www.ewg.org/hair-straighteners/our-report/how-to-get-straight-hair-whats-the-best-option/. April 2011.
  2. Occupational Safety and Health Administration. OSHA Fact Sheet: Formaldehyde. Osha.gov. https://www.osha.gov/OshDoc/data_General_Facts/formaldehyde-factsheet.pdf. April 2011.
  3. S. Food & Drug Administration. Hair-Smoothing Products That Release Formaldehyde When Heated. Fda.gov. https://www.fda.gov/cosmetics/cosmetic-products/hair-smoothing-products-release-formaldehyde-when-heated#:~:text=A%20hair%20straightening%20or%20smoothing,the%20air%20as%20a%20gas. Updated August 24, 2020.
  4. National Cancer Institute. Formaldehyde and Cancer Risk. Cancer.gov. https://www.cancer.gov/about-cancer/causes-prevention/risk/substances/formaldehyde/formaldehyde-fact-sheet#what-has-been-done-to-protect-workers-from-formaldehyde Updated June 10, 2011.
  5. Schwilk E, et. al. Formaldehyde and leukemia: an updated meta-analysis and evaluation of bias. Journal of Occupational and Environmental Medicine. 2010;52(9):878-886. https://journals.lww.com/joem/Abstract/2010/09000/Formaldehyde_and_Leukemia__An_Updated.5.aspx.
  6. Environmental Working Group. Brands that hide formaldehyde. ewg.org. http://www.ewg.org/hair-straighteners/our-report/hair-straighteners-that-hide-formaldehyde/. April 2011.
  7. New York State Department of Health. Consumer Health Alert: Hair Straightening Products and Formaldehyde. health.ny.govhttps://www.health.ny.gov/environmental/chemicals/formaldehyde/docs/consumer.pdf. Updated Feb 2024.
  8. Women’s Voices for the Earth. Hair Straightening Products Containing Formaldehyde. womensvoices.org. https://www.womensvoices.org/safe-salons/brazilian-blowout/hair-straightening-products-containing-formaldehyde/. Updated January, 2018.
  9. National Institute of Health. Hair straightening chemicals are associated with higher uterine cancer risk. https://www.nih.gov/news-events/news-releases/hair-straightening-chemicals-associated-higher-uterine-cancer-risk. 17 October 2022.
  10. Melillo, Gianna. Lawsuit against L’Oreal, beauty companies alleges hair straightening products cause uterine cancer. The Hill. October 25th, 2022. https://thehill.com/changing-america/well-being/prevention-cures/3703073-lawsuit-against-loreal-beauty-companies-alleges-hair-straightening-products-cause-uterine-cancer/
  11. S. Food and Drug Administration. Warning Letter: Brazilian Blowout 8/22/11. College Park, MD: U.S. Food and Drug Administration; August 22, 2011. https://www.fdalabelcompliance.com/letters/ucm270809.
  12. Maneli MH, Smith P, Khumalo, NP. Elevated formaldehyde concentration in “Brazilian keratin type” hair-straightening products: A cross-sectional study. Journal of the American Academy of Dermatology. 2013;70(2):276-280. https://www.jaad.org/article/S0190-9622(13)01135-3/fulltext#back-bib7
  13. Rabin RC. The FDA Wanted to Ban Some Hair Straighteners. It Never Happened. The New York Times. October 21, 2020. https://www.nytimes.com/2020/10/21/health/brazilian-blowout-formaldehyde-fda.html.Rabin, R. C., & Jewett, C. (2023, October
  14.  F.D.A. Plans to Ban Hair Straighteners With Formaldehyde. The New York Times. https://www.nytimes.com/2023/10/16/health/hair-straighteners-black-women-fda.html
  15. Nutrition, C. for F. S. and A. (2022). Hair Smoothing Products That Release Formaldehyde When Heated. FDA. https://www.fda.gov/cosmetics/cosmetic-products/hair-smoothing-products-release-formaldehyde-when-heated
  16. 1910.1048—Formaldehyde. | Occupational Safety and Health Administration. (n.d.). Retrieved February 15, 2024, from https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.1048