Hair Straightening Treatments Explained: Keratin, Brazilian Blow Dry, Japanese, Nanoplasty and Hair Botox (UK Guide)

Short answer: There are really only three families of salon straightening↓DOWN, whatever the menu calls them:

1. Smoothers (keratin, Brazilian blow dry, nanoplasty, “hair botox”). They coat and set the hair with heat and fade over weeks to months.
2. Thio straighteners (Japanese straightening, thermal reconditioning, rebonding). They break and rebuild the hair’s bonds: 80%+ of the curl out, for good on treated hair.
3. Relaxers (hydroxide). Also permanent. They’re a different chemistry and don’t mix with thio.

Everything else is marketing.

I’m Zoltan. I did my first perm in 1991 and my first straightening in 1999. I’ve worked in Mayfair since the Curzon Street days and have had my own chair on Maddox Street since 2018, with the work written up in Vogue, Harper’s Bazaar, Tatler and The Sunday Times along the way. I’ve also imported a Brazilian blow dry system into the UK myself. So I’ve seen these treatments from the salon side and from the supplier side.

1. Keratin and the Brazilian blow dry

What people search: “keratin treatment↓DOWN”, “Brazilian blow dry”, “keratin treatment for curly hair”, “how long does keratin last”.

What it does: a solution goes on, then the flat iron seals it in, often 15–20 passes on a section. In the classic formulas, formaldehyde crosslinks the hair’s keratin so it is “set” straighter. Here’s a fact most menus won’t tell you: research finds little evidence that the keratin in the bottle actually gets into your hair. The work is done by the chemistry and the heat.

How long: anything from about 6 weeks to 5 months depending on strength, washing and water.

Watch out for: formaldehyde and anything that releases it. It’s banned as an ingredient in UK cosmetics, but “releasers” exist and get released as gas when heated. Full detail in is keratin treatment safe.

2. Nanoplasty, “hair botox” and “formaldehyde-free” smoothing

What people search: “keratin treatment↓DOWN vs nanoplasty”, “keratin vs hair botox”, “hair straightening treatment nanoplasty”.

What it is: the names are brands and fashions, not chemistry. There’s no botox in hair botox. Many of these are acid-based smoothers, and some use glyoxylic acid. That ingredient is under investigation after French and Israeli doctors linked it to acute kidney injury. The EU’s scientific committee is reviewing it now. As of September 2026 there is no EU or UK restriction.

My rule: judge the product by its active ingredient and its amount, never by its name.

3. Japanese straightening, thermal reconditioning, rebonding

What people search: “Japanese hair straightening↓DOWN”, “permanent hair straightening”, “keratin treatment vs rebonding”.

What it does: a thioglycolate lotion breaks the disulphide bonds that hold your curl. The hair is rinsed, dried and ironed straight, then neutralised with an oxidiser that locks the new shape in. In GB law the professional strength is capped at 11% thioglycolic acid at pH 7–9.5.

How long: the treated hair stays straight. You only ever do the new growth.

Watch out for: hair that has been bleached or relaxed. Hair treated with a hydroxide relaxer shouldn’t then take a thio straightener. And never let anyone overlap onto hair that’s already been done.

4. Relaxers

Used mostly on very tight, coily hair. They’re hydroxide-based, with a GB professional limit of 4.5% sodium/potassium hydroxide and a legal “can cause blindness” warning. A large US study (NIH Sister Study, 2022) found an association between frequent relaxer↓DOWN use and uterine cancer. It doesn’t prove cause, but it’s worth knowing.

How I translate this to my own menu

You searched for…	What it is	My treatment	Lasts
Keratin / Brazilian / nanoplasty / hair botox	Smoothing, some curl reduction	Straightment Demi↓DOWN: about 60% of the curl out	6+ months
Frizz only, keep my shape	Surface smoothing	Straightment Semi↓DOWN	2+ months
Japanese / permanent / rebonding	Bonds rebuilt	Straightment Permanent↓DOWN: 80%+ out, for good	Roots ~12 months
“Someone else’s treatment went wrong”	Correction	Strand test first, then a written plan	—

I hold several systems and strengths and choose at the chair. A salon with one product has to make every head fit that product.

Straight talk: “Best hair straightening treatment” is the wrong question. The right one is “what’s the gentlest thing that gets my hair where I want it?” Sometimes the honest answer is a good cut and a better brush.

More straight talk → The Brief

Where you live changes the answer

Humidity and water hardness vary a lot across the UK and Ireland. Chalk-hard water in Brighton and East Anglia behaves differently from soft upland water in Manchester or Glasgow, and 170 rain days behaves differently from 110. I’ve written a guide for each region: South East, London, South West, East of England, Midlands, North West, Yorkshire, North East, Scotland, Wales, Northern Ireland, Ireland.

— Zoltan

Sources

• Dias, Int J Trichology 2015 — chemistry of straighteners
• de Paula et al., An Bras Dermatol 2022 — review of straightening
• Dermatology Times — keratin duration
• OSHA — formaldehyde in hair smoothing products
• GB Cosmetics Regulation Annex III — thioglycolic acid and hydroxide limits
• ANSES (France) — glyoxylic acid alert, Jan 2025; EU call for data
• American Cancer Society on the NIH Sister Study