Is Keratin Treatment Safe? Formaldehyde, Glyoxylic Acid and the UK Rules in 2026

Short answer: It depends on what’s in the bottle and who’s holding the iron.

• Formaldehyde is classed as a Category 1B carcinogen and is banned as an ingredient in UK cosmetics.
• Ingredients that release formaldehyde are still allowed. Since 15 July 2026, a product must be labelled “releases formaldehyde” if it releases 0.001% or more (the old threshold was 0.05%). Shops can sell off old-label stock until 14 January 2027.
• Glyoxylic acid, the usual “formaldehyde-free” alternative, is under EU review after reports of kidney injury. It is not banned as of September 2026.

I’m Zoltan, a texture specialist in Mayfair since 2018 and straightening↓DOWN hair since 1999. This is the page I wish every client read before they booked anywhere, including with me.

Formaldehyde: what’s actually banned

Formaldehyde crosslinks the hair and holds it straight. That’s why the old Brazilian formulas worked so well. It’s also why it’s banned: it’s a Category 1B carcinogen, prohibited in cosmetics under Annex II in both the EU and GB.

The catch is that it has other names: methylene glycol, methanediol, formalin, methanal. Heat a methylene glycol solution with a flat iron and you get formaldehyde gas. The US workplace safety agency (OSHA) warns that products labelled “formaldehyde free” can still expose people to it.

What changed in 2026: the UK’s new rules (SI 2026/23) came into force on 15 July 2026. Any product releasing 0.001% or more formaldehyde must say “releases formaldehyde” on the label. The EU made the same change earlier.

In the US: the FDA has missed deadline after deadline on its promised formaldehyde ban since 2023. As of April 2026 it was “still developing the proposed rule”. So don’t assume an American product is regulated to UK standards.

Glyoxylic acid: the “safe” alternative that isn’t settled

When formaldehyde got its bad name, much of the industry moved to glyoxylic acid. Then the reports started:

• Israel (2023): 26 patients with acute kidney injury after straightening↓DOWN. Three needed temporary dialysis.
• France (NEJM, 2024): one woman had kidney injury three times, each soon after a straightening. In mice, the product caused kidney damage within 24 hours.
• France (ANSES, January 2025): five cases. The agency called glyoxylic acid “very likely responsible” and asked for EU action “restricting or even banning” it.

The European Commission collected data until April 2026. In May 2026 it asked its scientific committee whether up to 16% is safe in straighteners, with answers due in 2027. Until then it’s legal, and it’s in a lot of “nanoplasty”, “hair botox” and “organic keratin” products.

Straight talk: I’m not telling you glyoxylic acid will hurt you. I’m telling you the question is open, and you’re allowed to ask what’s going on your head. A good hairdresser can tell you the active ingredient by name. If yours can’t, that’s your answer.

More straight talk → The Brief

Is keratin bad for your hair?

Mostly the damage isn’t the chemistry. It’s:

• Heat: an iron at the top setting, 20 passes, on fine or bleached hair.
• Wrong strength: a thick-curly formula on fine wavy hair.
• Layering: keratin on top of a previous straightener on top of a box dye, with nobody asking.
• Overlapping: re-treating hair that’s already been done, every visit, until it snaps.

Five questions to ask any salon, including mine

1. What’s the active ingredient, and does this product release formaldehyde?
2. Can I see the ingredient list?
3. Will you strand test my hair first?
4. Is the room ventilated or extracted?
5. Will you treat only new growth next time?

Pregnancy, asthma, kidney problems

I’m a hairdresser, not a doctor. There’s no solid safety data for chemical straightening↓DOWN in pregnancy. If you’re pregnant, have a kidney condition or have breathing problems, ask your GP or midwife first, and tell your hairdresser.

So is it worth it?

For the right hair, with the right product, yes. It can give you back an hour a day. For hair that’s bleached to the edge, often no. Then a cut, a gentler smoothing↓DOWN or a correction plan is the honest answer. See the three families of straightening, or if something’s already gone wrong, keratin ruined my hair: what now.

Not sure? The online consultation is £9.95 and gets you a straight answer before you spend hundreds.

— Zoltan

Sources

• GB SAG-CS Opinion 16 — formaldehyde and formaldehyde-releasing substances (2024)
• The Cosmetic Products (Amendment) Regulations 2026, SI 2026/23
• EU Regulation 2022/1181
• OSHA — hair smoothing products
• CNN via KRDO — FDA misses formaldehyde ban deadline (Jan 2026); Fox34 (Apr 2026)
• Bnaya et al., Am J Kidney Dis 2023
• NEJM 2024 letter, summarised
• ANSES — glyoxylic acid alert confirmed (Jan 2025)
• European Commission — call for data on glyoxylic acid; SCCS mandate, May 2026