Are Keratin Treatments Safe? Formaldehyde, the Kidney Injury Warning, and Where the FDA Ban Stands (November 2026)

Are keratin treatments safe? It depends a lot on what is in the bottle. Older formulas give off formaldehyde gas when the flat iron heats them, and formaldehyde can cause cancer. Many newer "formaldehyde-free" formulas swap in glyoxylic acid, which health officials in France now link to sudden kidney injury in some women. Meanwhile, the U.S. ban on formaldehyde in these products still has not been proposed.

This guide covers what is in smoothing treatments, the 2026 kidney cases, where U.S. and EU rules stand right now, what women who had them say, and what to ask before you book.

Short answer

Formaldehyde smoothing is a real risk. Heat turns it into a gas you and your stylist breathe in. It irritates eyes, nose, and lungs, and long or high exposure is tied to cancer.
"Formaldehyde-free" is not the same as safe. Many of these use glyoxylic acid. A December 2025 review found 34 women with kidney injury after hair straightening, and in 20 of 36 cases the product was sold as formaldehyde-free.
The U.S. ban is still stuck. The FDA's planned rule has been under White House review since August 6, 2026, with a target of November 2026. It has been delayed since 2023.
The EU is reviewing glyoxylic acid now. Its safety panel took the job on April 30, 2026 and has 12 months.
Bottom line: if you get one, know the exact product and its ingredients first. If the salon cannot tell you, skip it.

What is in a keratin treatment?

The name is mostly marketing. The keratin in the bottle does not do the straightening. The work is done by chemicals that reshape the hair when a flat iron heats them. The two big ones:

Formaldehyde, also listed as formalin or methylene glycol. The FDA says heating it releases formaldehyde gas into the air. Above 0.1 parts per million, some people get watery, burning eyes, a sore throat, coughing, wheezing, nausea, and skin irritation. Repeated contact can also cause skin allergies.
Glyoxylic acid and related acids. These are the main swap in many "formaldehyde-free" treatments. The body can turn it into oxalate, the same stuff in many kidney stones, which can form crystals in the kidneys.

The kidney injury cases

The review. A systematic review published in December 2025 pulled together 34 patients with 36 cases of kidney injury after hair straightening. Every patient was female, the average age was about 29, and the youngest was 10. Kidney injury showed up a median of 2 days after treatment. Most had vomiting (81%) or nausea (69%). Six cases needed dialysis. All patients recovered.
France (February 24, 2026). France's health safety agency said 15 new cases had been reported in France since October 2024. Lab tests found glyoxylic acid in at least three products that did not list it on the label. In its first case, a woman had kidney injury three times in three years, each time hours after a smoothing treatment. Her scalp burned during each one and later broke out in sores, and low back pain started within an hour after.
A 26 year old woman (March 2026). Three days after a salon straightening sold as formaldehyde-free, she had nausea, vomiting, and pain in both sides of her back. She had severe kidney injury. Her scalp had itched and turned red right after the product went on. She recovered within a month with treatment.
A 39 year old woman (June 2026). After chemical hair products, she had vomiting, diarrhea, and back pain. A kidney biopsy found oxalate crystals. She also fully recovered with treatment.
Israel (August 6, 2026). The Health Ministry warned against products from a chain of straightening shops. One unregistered smoothing gel contained glyoxylic acid, and formaldehyde, which is banned in cosmetics there, was also found.

French officials list these warning signs of kidney trouble during a treatment or in the hours after it: low back or belly pain, nausea or vomiting, and unusual tiredness. Some of their cases also had headaches and strong thirst. They say this applies even if the label does not list glyoxylic acid, so mention the hair treatment if you get checked.

New research (2026)

A lab study says normal use is fine. A July 2026 study measured how much of two products on the market gets through the skin during a realistic treatment. It estimated the oxalate a client takes in is 20 to 41 times lower than what the body normally gets from food and makes on its own, and said there were no health concerns under the conditions tested. That clashes with the case reports, which may involve stronger products, mislabeled ones, or people who react more. The EU review is meant to sort this out.
What else is in these products. A June 2026 review of 21 studies found keratin treatments more often contain formaldehyde or chemicals that release it, while relaxers more often contain hormone disrupting chemicals and fragrance. Several of the studies also found stylists may get more exposure than clients.
Stylists' lungs. An April 2026 study of 41 female salon workers who do keratin treatments found their lung test scores were lower than expected for people like them.
Cancer links are still being studied. A 2026 study of more than 46,000 U.S. women found using hair straighteners or relaxers was tied to higher rates of thyroid and pancreatic cancer. It shows a link, not proof that the products caused it, and the authors saw little sign that more use meant more risk.

Where the rules stand (November 2026)

U.S. The FDA first planned to propose a ban on formaldehyde and chemicals that release it in heated smoothing products for October 2023. Its current agenda lists November 2026. The rule has been sitting in White House review since August 6, 2026. Even once proposed, it would need a public comment period before any final ban. It also does not cover glyoxylic acid.
States. California, Maryland, and Washington already restrict formaldehyde in cosmetics. Washington adds limits on more formaldehyde releasing chemicals starting January 1, 2027.
EU. Formaldehyde is already banned in EU cosmetics, which is why glyoxylic acid took over there. The EU's consumer safety panel agreed on April 30, 2026 to decide whether glyoxylic acid is safe at up to 16% in hair straighteners, or what lower amount would be. It has 12 months.

What people who tried it say

Greasy and still frizzy. In late October 2026, one woman with curly, frizzy hair said that a week after a salon smoothing treatment, her hair was flat, greasy, and still frizzy, and she still needed as much heat as before. She asked how to make it wash out faster.
New stylist, new problem. A woman who had done keratin for years without trouble said that after switching to a new stylist, her hair turned so oily she had to wash it every two days.
It does not last on fine hair. A woman with very fine hair said she had heard treatments last only 2 to 3 months on hair like hers, and she wanted something that lasted 6. Another woman said she has done keratin every 10 weeks for almost 20 years, and is moving to at home kits because salons cost too much.
Color change. One woman said a keratin treatment turned her untreated off black hair dark brown.
Curls that do not come back. A teen growing out years of keratin treatments said the bottom half of her hair would not curl anymore, even after a curly cut. A woman a year into growing hers out said her ends were always dry and kept breaking.
Hair loss worries. A woman with female pattern hair loss said her thinning curls had turned loose and frizzy, and asked if a keratin treatment would make the shedding worse.
Scared off by the chemicals. A young woman asking about keratin said the formaldehyde part scared her because it can cause cancer.

Lesser-known tips

Ask for the Safety Data Sheet. Salon products may not carry a full consumer ingredient list, but the salon must have a safety sheet for staff. Look for formaldehyde, formalin, methylene glycol, and glyoxylic acid or "glyoxyloyl" ingredients.
Do not trust names. "Brazilian," "Japanese," "nanoplasty," "botox," and "organic" are not ingredients. French officials found glyoxylic acid in products that did not list it.
A burning scalp is not normal. In the French case, scalp burning during the treatment came before each kidney injury. If your scalp burns or itches hard, ask for it to be rinsed off.
At home kits carry the same risk. French officials warned that these products are sold straight to shoppers, not just to salons. At home, you also have nobody checking ventilation or timing.
Fumes are a sign. If your eyes sting and the room smells sharp when the iron hits your hair, formaldehyde is likely in the air.
Think about your stylist too. She breathes this all day. A salon that uses strong fans, opens doors, and knows its products is a better sign than one that just says "it's safe."
Stack with care. Several posters asked about doing color and keratin close together. Each one weakens hair, and doing both quickly is how breakage happens.

Fair take

What supporters say: a good smoothing treatment can cut frizz for months, save hours of blow drying, and mean less heat damage from daily flat ironing. Many women have done them for years with no health problems.

What the evidence says: formaldehyde based treatments expose you and your stylist to a known cancer causing gas. The common swap, glyoxylic acid, has been tied to rare but serious kidney injury, sometimes from products that did not even list it. Every patient in the 2025 review recovered, but some needed dialysis first. And U.S. rules have not caught up.

Bottom line

Keratin treatments are not harmless salon fluff. Formaldehyde ones mean breathing in a cancer causing gas, and some "formaldehyde-free" ones carry a small but real kidney risk. If you still want one, know the exact product and its ingredients, choose a well aired salon, and stop if your scalp burns. If nobody can tell you what is in the bottle, walk out. And if you are refreshing your look for dating photos, The Face They See lets people of the opposite gender rank your photos for free.

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