Keratin vs Japanese Straightening vs Brazilian Blow Dry: Which One, How Long It Lasts, What It Costs

Short answer:

• Keratin = Brazilian blow dry. Same family, different name. It smooths and softens, takes out some curl and fades over weeks to months.
• Japanese straightening rebuilds the hair’s bonds. 80%+ of the curl out, for good on treated hair, and you only ever do the roots.
• Frizz? Keratin. Curl you want gone? Japanese-style permanent. Unsure? Get a consultation before either.

I’m Zoltan, Mayfair: perming↑UP since 1991, straightening since 1999. I’ve used, sold and fixed all three. Here’s the comparison people actually ask me for.

Side by side

Compared	Keratin / Brazilian blow dry	Japanese / permanent straightening
What it does	Heat-seals a smoothing solution; loosens curl	Breaks and rebuilds disulphide bonds
Result	Smoother, softer, less frizz, some curl left	Straight on the treated hair
Lasts	~6 weeks to 5 months (stronger demi: 6+)	Permanent; roots every ~6–12+ months
Wash-out?	Yes, gradually	No
Line of regrowth	Soft, blends	Visible when roots grow
Time in chair	2–3 hours typical	3–6 hours typical
Risky on	Very bleached hair, too much heat	Bleached, relaxed or previously thio-treated hair
Main chemistry	Aldehydes (formaldehyde-releasers) or acids (e.g. glyoxylic)	Ammonium thioglycolate + neutraliser

Chair times are typical ranges. Your time depends on length and density and is confirmed when you book.

“Keratin treatment vs…” the other names

• vs nanoplasty / hair botox: same family as keratin, usually acid-based. Judge by the ingredient, not the name.
• vs rebonding: rebonding is the Asian name for thio straightening↓DOWN. Same family as Japanese.
• vs relaxer: a relaxer is permanent too, but hydroxide-based, and it doesn’t mix with thio. Never let anyone put one over the other.
• vs “smoothing”: that’s the category keratin is in.

Curly hair: which one?

This comes up constantly in what people search. The honest answer:

• You love your curls and hate the frizz → don’t straighten↓DOWN. Try a surface smoothing at most. Google autocompletes “keratin treatment ruined my curls” for a reason, and I believe every one of those people.
• You want looser, easier curls → a demi-permanent smoothing at the right strength. Mine, Straightment Demi↓DOWN, removes about 60% of the curl, and what it removes stays out.
• You want straight → permanent. Straightment Permanent↓DOWN takes out 80%+ of the curl on the treated hair, for good.

Straight talk: If a salon says keratin will make tight curls poker straight and then “wash out back to your curls”, one half of that sentence isn’t true. Treatments strong enough to straighten tight curl don’t fully wash out. Treatments that fully wash out don’t straighten tight curl.

More straight talk → The Brief

What it costs in the UK

Prices vary a lot by city, salon and hair length, and I can’t verify other salons’ prices, so I won’t quote them. Mine are by length band, from above the shoulder (S) to past the waist (XXL):

• Straightment Semi↓DOWN (smoothing↓DOWN, 2+ months): £149.95–£269.95
• Straightment Demi↓DOWN (the “keratin” job, 6+ months): all-over £219.95–£569.95 depending on length and whether hair is fine/wavy or thick/curly. Roots-and-refresh inside your window costs less.
• Straightment Permanent↓DOWN (the “Japanese” job): all-over £459.95–£789.95; roots-and-refresh from £369.95
• Correction: from £449.95, only after a strand test

Blow dry and finish are included on Demi and Permanent.

How long does keratin take in the salon?

Usually a couple of hours, longer on long thick hair. There’s no “express” shortcut that does the same job. An express treatment is a weaker treatment.

Which one lasts longest on wavy hair?

Permanent lasts longest by definition. On loose waves, a demi smoothing↓DOWN often gets you 90% of what you wanted for half the commitment. That’s usually where I’d start.

Still torn? Book the £9.95 online consultation. Fifteen minutes, your hair on camera, a straight answer.

— Zoltan

Sources

• Dias, Int J Trichology 2015
• de Paula et al., An Bras Dermatol 2022
• Dermatology Times — keratin 6 weeks to 5 months
• GB Cosmetics Regulation Annex III
• Search phrases taken from Google UK autocomplete, 26 Sep 2026