Keratin straightening, glyoxylic acid and kidney injury: what to know
Acute kidney injury cases after straightening with glyoxylic acid, ANSES advice from January 2025, what to check on the label and which symptoms need a doctor now.
- In January 2025 ANSES, France's health safety agency, concluded that glyoxylic acid in straightening products is highly probably the cause of acute kidney injury cases.
- Symptoms usually start during the treatment or within a few hours: lower back or abdominal pain, nausea, vomiting, sometimes a burning or sore scalp.
- If you get these symptoms after straightening, see a doctor promptly and say you have just had your hair straightened.
- Check the label for Glyoxylic Acid and Glyoxyloyl ingredients. If you're unsure, ask the salon to show you the ingredients first.
Some “keratin” or “Brazilian” straightening products use glyoxylic acid to straighten the hair, and cases of acute kidney injury (AKI) after these treatments have been reported in Israel, France, Switzerland and elsewhere. In January 2025 France’s health safety agency, ANSES, concluded that glyoxylic acid is highly probably the cause and advised not using these products for now. This article covers what happened, how to read the label, and which symptoms mean you should see a doctor straight away, without treating every straightening method as dangerous.
How glyoxylic acid ended up in straighteners
Brazilian straightening used to rely on formaldehyde, which has been completely banned in cosmetics in Europe since 2019 because it causes cancer. Makers looked for replacements, and glyoxylic acid is one of them. ANSES says straighteners usually contain about 3-10%, but levels range from 0.1% to over 25%.
A typical treatment goes like this: the solution is applied to washed hair, strand by strand, left for 10-60 minutes and not rinsed out; the hair is then blow-dried and flat-ironed at around 200°C. Makers usually advise keeping the product 0.5-1 cm away from the scalp.
ANSES explains that a very acidic product, heat and long contact all help the substance pass through the scalp, especially if the scalp is already irritated or broken.
What the case reports tell us
| Report | What was found |
|---|---|
| Israel (Bnaya et al. 2023, summarised by ANSES) | 26 patients aged 13-58. Symptoms started during or within 3 hours of the treatment. 10 (38%) had a scalp rash. Of 7 kidney biopsies, 6 showed calcium oxalate crystals. Kidney function returned to normal in every patient whose outcome was known. |
| Switzerland (Huber et al. 2024) | A 42-year-old woman with right flank pain, nausea and vomiting. Biopsy showed many calcium oxalate deposits. No dialysis was needed. |
| France (cosmetics vigilance scheme) | One woman had AKI three times, after three straightening treatments. Two more cases in 2024 involved products with 9% and 12.5% glyoxylic acid. |
| ANSES total | 46 cases identified, which it believes is an undercount. |
The proposed mechanism: the body turns glyoxylic acid into oxalate, which binds calcium and forms crystals that lodge in the kidneys, much like ethylene glycol poisoning.
Lower back or abdominal pain, nausea or vomiting within hours of a straightening treatment: don’t wait. See a doctor and say you’ve just had your hair straightened.
Worked example: reading kidney numbers from a real case
Blood creatinine is used to track kidney function; the higher it goes, the less waste the kidneys are filtering. ANSES gives a general normal range for women of 50-100 µmol/L. Here is one French case (a 38-year-old woman, product with 9% glyoxylic acid):
- Her baseline from the year before: 58 µmol/L.
- Two days after the treatment: 117 µmol/L.
- 117 ÷ 58 = 2.02, so roughly double, which doctors classify as stage 2 acute kidney injury (KDIGO 2).
- Note that 117 looks close to the “normal” 50-100, but for her it was double her usual value. Doctors compare against each person’s own baseline.
- With fluids, calcium supplements and a low-oxalate diet as her doctor advised, it fell to 93 on 15 July and was back to 88 µmol/L on 22 July.
Compare the far more serious Swiss case: 584 µmol/L on admission, 238 at discharge and 77 µmol/L three months later.
The example is here to show why testing matters, not so you can interpret your own blood results.
Symptoms that need a doctor
ANSES advises both clients and hairdressers that if any of these appear during the treatment or in the hours after it, they should see a doctor promptly or call a poison control centre, and mention the straightening product:
- abdominal pain or lower back pain (around the kidneys)
- nausea or vomiting
- unusual tiredness
- a burning scalp during the treatment, or scabbed sores afterwards, which came alongside the symptoms above in several cases
These symptoms are not specific and can have other causes; blood and urine tests sort that out. The key thing is to tell the doctor about the straightening, so they consider it.
Reading the label and talking to the salon
Ingredient (INCI) names to look for:
| Name on the label | Note |
|---|---|
| Glyoxylic Acid | The one ANSES advises not to use |
| Glyoxyloyl Carbocysteine | A derivative that can break down into glyoxylic acid in acidic, heated products; ANSES says to watch it too |
| Glyoxyloyl Keratin Amino Acids | Another derivative group ANSES flags |
Before a treatment, ask to see the product box or label. If the salon can’t tell you what’s in it, you don’t have enough information to decide. How to read an ingredient list is covered in Reading a cosmetic ingredient list.
If you still want straight hair, careful blow-drying and flat-ironing doesn’t involve these chemicals. See Blow-drying, straightening and curling with less damage.
Where the rules stand
- Israel banned straighteners containing glyoxylic acid in 2022 (but not its derivatives).
- In France, ANSES’s opinion of 21 January 2025 advised against using them and asked for a European risk assessment.
- The European Commission ran a call for safety data on glyoxylic acid in cosmetics from 9 April 2025 to 8 April 2026. The next step is an assessment by its Scientific Committee on Consumer Safety (SCCS). At the time of writing, the EU has not restricted it.
No ban doesn’t mean safe; it means the assessment isn’t finished.
Common mistakes
| Doing this | Why it’s a problem |
|---|---|
| Assuming “formaldehyde-free” means safe | Many replacement formulas use glyoxylic acid |
| Putting up with a burning scalp during treatment | An irritated scalp absorbs more |
| Straightening with a sore scalp or inflamed dandruff | The first French patient had regular dandruff and developed sores after treatment |
| Blaming back pain afterwards on sitting too long | Symptoms can start within the first hour; get checked |
| Seeing a doctor but not mentioning the treatment | They may not think of this cause |
| Repeating the treatment after a reaction | The French patient reacted every time |
This article is general information, not a diagnosis. If you have kidney disease or have had kidney stones, talk to your doctor before any chemical hair treatment.
Sources
FAQ
Does every keratin treatment risk kidney failure?
No. Reported cases number in the tens, and nobody knows how many treatments were done in total, so there is no risk rate. But some cases were serious enough for hospital, which is why ANSES advises avoiding products with glyoxylic acid for now.
Is a formaldehyde-free straightener safer?
Not necessarily. After Europe banned formaldehyde in cosmetics, many replacement formulas turned to glyoxylic acid and related ingredients. Check the actual ingredient list.
Does the kidney recover?
In the reported cases with follow-up, kidney function mostly returned to normal after treatment, but one woman had it happen again each time she had her hair straightened. Getting seen early helps a lot. Don't wait it out.
General guidance. Products differ between brands: always follow the label. If you react to a product, see a doctor.