QUICK ANSWER
Hair smoothing and straightening treatments range from semi-permanent protein coatings like keratin to permanent bond-restructuring systems like Japanese straightening, rebonding and relaxers. The right choice depends on how straight you want to go, how long you want it to last, and what your hair has already been through. This guide covers every method used anywhere in the world.
WHY TRUST THIS GUIDE
Written by [ZOLTAN — one line: name, Mayfair salon, years behind the chair]. I don't sell most of these treatments — I advise on them, and I see the results (good and bad) walk into my chair every week. No salon selling you one system will tell you what the rival system does better. This guide will.
HOW TO CHOOSE — THE FOUR QUESTIONS
1. HOW STRAIGHT? Frizz-free with movement (keratin, hair botox, smoothening) — or pin-straight (Japanese straightening, rebonding, relaxer, magic straight).
2. HOW PERMANENT? Washes out gradually over months (keratin family, nanoplastia) — or permanent on treated lengths with a regrowth line (rebonding, Japanese, relaxers).
3. WHAT HAS YOUR HAIR BEEN THROUGH? Bleach, henna, old relaxers and previous straightening all change what is safe. Permanent systems and compromised hair are a dangerous mix; coating systems are more forgiving.
4. WHAT CHEMISTRY WILL YOU ACCEPT? Aldehyde systems (the formaldehyde debate), acid systems (glyoxylic), thio and hydroxide systems (permanent restructuring), or protein-only repair. Each has a different risk and result profile.
THE MASTER COMPARISON
Keratin treatment — smooths, loosens curl ~50% — 3-5 months, fades out — keratin + aldehyde or acid.
Nanoplastia — smooth to very straight — 4-6 months, fades out — glyoxylic acid + amino.
Hair botox — repair, de-frizz, minimal straightening — 2-4 months — proteins and fillers, no botulinum.
Brazilian blowout — smooths, keeps body — 3 months — acid/aldehyde keratin.
Hair smoothening — relaxed, natural fall — 4-6 months — cysteine or acid systems.
Japanese straightening — pin-straight, glass finish — permanent + regrowth — thio + heat.
Hair rebonding — pin-straight — permanent + regrowth — thio/alkaline + heat.
Magic straight perm — pin-straight, Korean finish — permanent + regrowth — alkaline + iron.
Relaxer — straightened afro texture — permanent + regrowth — hydroxides (lye/no-lye).
Silk press — pin-straight, no chemicals — until the next wash — heat only.
Escova progressiva — the Brazilian original, smooth-straight — 3-4 months — historically formol; now banned actives.
Brazilian blow dry — UK name for keratin smoothing — 3-4 months — keratin systems.
Permanent hair straightening — umbrella term — varies — varies.
THE SEVEN FAMILIES
1. THE KERATIN FAMILY — semi-permanent protein coatings sealed with heat. The world's most-booked smoothing category. Start with our complete guide to keratin treatments, the story of the Brazilian blowout, and what the UK calls a Brazilian blow dry or permanent blow dry.
2. THE REBONDING FAMILY — Asia's permanent pin-straight systems. Read the full guide to hair rebonding and its dozens of regional variants.
3. JAPANESE SYSTEMS — where permanent straightening was perfected. The definitive guide to Japanese hair straightening and thermal reconditioning, plus the modern acid wave.
4. KOREAN SYSTEMS — the magic straight culture: straight with life in it. Full guide to the magic straight perm and its volume variants.
5. RELAXERS AND AFRO-HAIR METHODS — the oldest category, from hydroxide relaxers to the chemical-free silk press.
6. THE NEW GENERATION — Brazil's post-formol wave: nanoplastia, hair botox, and the original escova progressiva that started everything. Also see India's favourite, hair smoothening.
7. EMERGING TECH — exosomes, cryotherapy, graphene and friends. We publish these only after verification.
And if you just want the umbrella explained: what "permanent hair straightening" actually means.
BROWSE BY FAMILY
Deep-dive hubs for every family: the keratin family, the rebonding family, Japanese systems, Korean systems, relaxers and afro-hair methods, the new generation plastia family, and emerging tech, filtered for hype.
THE REGULATION SNAPSHOT
Brazil's regulator ANVISA bans formaldehyde as a straightening active and, since mid-2025, glyoxylic acid too — the base of most "formol-free" systems. The US FDA proposed a formaldehyde ban in 2023 that remains stalled. Direction of travel worldwide: harsh actives out, gentler acid and amino systems in. Ask any salon what is in the bottle; a good one answers instantly.
AFTERCARE — THE TRUTHS THAT APPLY TO EVERY TREATMENT
Whatever you choose: sulfate-free and salt-free washing, real heat protection, a weekly protein or moisture mask matched to your system, and serious respect for sea, chlorine and hard water. Aftercare is the difference between five months and five weeks — every treatment page here ends with the exact routine for that system.
EDITOR NOTE: PRODUCT SLOT — aftercare range
EDITOR NOTE: EMAIL CAPTURE — Download the free universal aftercare guide (PDF)
FAQ
Q: What is the difference between smoothing and straightening?
A: Smoothing treatments (keratin, botox, smoothening) coat and loosen the hair, killing frizz while keeping movement, and fade out over months. Straightening systems (Japanese, rebonding, relaxers) permanently restructure the hair's bonds for a pin-straight result that grows out rather than washes out.
Q: Which treatment is the least damaging?
A: Generally the ones that do the least: hair botox and protein smoothing sit at the gentle end, keratin and acid systems in the middle, and permanent restructuring systems (rebonding, Japanese straightening, relaxers) at the strong end — safe in expert hands, punishing in bad ones.
Q: Which lasts the longest?
A: Permanent systems last forever on the treated lengths — Japanese straightening, rebonding and relaxers only need root touch-ups as new hair grows. Among wash-out treatments, nanoplastia and keratin lead at roughly four to six months with correct aftercare.
Q: Can curly hair be safely straightened?
A: Yes, with the right match: the curlier and more fragile the hair, the more the choice matters. Tight curl patterns do best with either expert permanent systems on healthy hair or gentle smoothing on compromised hair — never a strong system on damaged curls.
Q: Are these treatments safe?
A: The honest answer: it depends on the chemistry and the salon. Formaldehyde-releasing formulas are the documented risk and are being regulated out worldwide; modern acid, cysteine and protein systems applied in ventilated salons are considered low risk for most people. Every treatment page here has a safety section.