Keratin Treatment in Japan: What You're Actually Getting
If you've searched for a keratin treatment in Japan, you've probably found the results confusing. Some salons call it a keratin treatment. Others call it a hair quality improvement treatment, an acid treatment, or an acid-heat treatment. A few will tell you they don't offer keratin at all — and then describe something that sounds exactly like it.
This isn't marketing spin. The categories genuinely differ between markets, and the naming has not caught up with the chemistry. Here's what's actually happening, so you can book with confidence.
The one thing that separates every smoothing service
Hair holds its shape through disulfide bonds — sulfur-to-sulfur links inside the hair fiber. These bonds are why your hair is curly, wavy, or straight, and why it returns to that shape after you wash it.
Every smoothing service in the world falls into one of two camps: it either breaks those bonds, or it doesn't
Everything else — the branding, the price, the country of origin — is downstream of that single question.
Japanese Straightening | Brazilian Keratin | Japanese Acid-Heat | |
Disulfide bonds | Broken and rebuilt | Untouched | Untouched |
What it does | Rewrites hair structure | Adds cross-links | Adds cross-links |
Iron temperature | 180–200°C | ~230°C | 180–200°C |
Lasts | Permanent | 3–5 months | 6–8 weeks |
How it ends | Grows out in a line | Washes out gradually | Washes out gradually |
Reversible | No | Yes | Yes |
Works on tight curl | Yes | Partially | No |
Camp 1: Japanese straightening
Japanese straightening (shukumou kyousei) uses a reducing agent to break the disulfide bonds, reshapes the hair with a flat iron, then uses an oxidizing agent to rebuild those bonds in the new position.
The internal structure of your hair is genuinely rewritten. The treated section stays straight permanently — it never reverts, and it never washes out. As your hair grows, you get a visible line where the new growth begins.
This is the strongest option available, and the only one that reliably straightens tightly curled hair. It's also irreversible, which is exactly why it deserves careful thought.
Camp 2: Keratin treatments and acid-heat treatments
Neither of these touches your disulfide bonds.
Instead, they add new bonds. An agent penetrates the hair, heat from a flat iron triggers a reaction, and cross-links form inside the fiber that hold it in a smoother configuration. Because your original structure is untouched, the effect gradually washes out and your hair returns to itself.
This is the camp most people actually want. It's also where the naming confusion lives.
Brazilian keratin and Japanese acid-heat are closer than you think
Traditional Brazilian keratin treatments used formaldehyde — or methylene glycol, which becomes formaldehyde in solution — combined with hydrolyzed keratin and very high iron temperatures, often around 230°C. It worked well and lasted three to five months.
It also created a workplace air quality problem serious enough that OSHA began issuing hazard alerts to salons in 2010. Regulation followed, and the industry moved.
The replacement the global industry settled on is glyoxylic acid. Today, a large share of treatments sold worldwide as "Brazilian keratin" are glyoxylic acid based. Meanwhile, glyoxylic acid is also the primary active in what Japanese salons have been calling acid-heat treatment since around 2019.
So the honest answer is: in 2026, these are frequently the same chemistry under two different names.
So what actually differs now?
Not the ingredient list, in many cases. The differences are in how the treatment is designed and performed:
Concentration and pH. Japanese formulations tend to run gentler, prioritizing fiber reinforcement over aggressive curl suppression.
Iron temperature. Traditional Brazilian protocols run hot — around 230°C. Japanese acid-heat typically works at 180–200°C. Lower heat means less cuticle stress, and also less forced straightening.
Tension and technique. How hard the hair is pulled during ironing, and how many passes are made, substantially changes the result from the identical product.
Intent. This is the real divide. A Brazilian protocol is designed to suppress curl. A Japanese acid-heat protocol is designed to improve texture — shine, softness, manageability, and resistance to humidity swelling.
Same family. Different goals.
What to realistically expect
We would rather you book knowing this than find out afterward.
Duration: six to eight weeks. Shorter than the three to five months often quoted for Brazilian treatments. The bonds formed are reversible — water gradually breaks them down, so every wash takes a little of the effect with it. A sulfate-free shampoo meaningfully extends this.
It fades, it doesn't grow out. There's no harsh regrowth line to manage. The effect softens evenly, which most people find easier to live with.
It is not straightening. If your hair is wavy, it will be smoother, glossier, and far less prone to puffing up in humidity — but it will still be wavy. If you want genuinely straight hair, you want Japanese straightening, and that's a different conversation.
Color will fade slightly faster. Glyoxylic acid is known for this. It's manageable, and it's the reason we keep a second formula on hand.
Who this treatment is not for
If your hair is Type 1–2C, you're a good fit. Book a katin smoothing treatment in Sapporo, or send us a photo first.
Straightforwardly: tightly curled and coily hair, roughly Type 3B and above.
Acid-heat treatments will not deliver the smoothing you're looking for on this hair type. The chemistry isn't strong enough, and the only service that genuinely performs here is full Japanese straightening — a four-hour, irreversible commitment that we don't offer.
We'd rather tell you this now than take your booking and disappoint you. If this is your hair type, please look for a salon that specializes in textured hair.
Best results come from straight to wavy and loosely curly hair — Type 1 through 2C — particularly if your concerns are frizz, puffiness, humidity swelling, or roughness from coloring.
Two formulas, and why we keep both
Most salons carry one product. We carry two, because the right choice depends on what's actually wrong with your hair.
Control — glyoxylic acid. Stronger frizz suppression and more body. This is the one for hair that swells, puffs, and loses its shape the moment humidity rises.
Color Safe — levulinic acid. Gentler, and notably kinder to your color. If you're blonde, recently lightened, or have a tone you've paid to protect, this is the one. The finish leans toward gloss and softness rather than control.
Control | Color Safe | |
Active | Glyoxylic acid | Levulinic acid |
Strongest at | Frizz and humidity control | Gloss and softness |
Adds | Body and structure | Slip and lightness |
Colour fade | Slightly faster | Minimal |
Choose it if | Your hair swells and puffs | You are blonde or recently lightened |
You don't need to decide in advance. We work it out together during consultation, based on your hair and your history. Pricing and duration for both are on the Keratin Smoothing Treatment menu.
Before your next chemical service
This matters and is rarely explained, so please read it.
The bonds this treatment creates sit inside your hair, and while they're there, they physically slow the penetration of other chemicals. The visible effect fades before the chemical influence does.
Service | When | Why |
Colour, gloss, toner | Same day is fine | No interference |
Bond builders, treatments | Same day is fine | Compatible |
Perm or relaxer | Wait 1–3 months | Cross-links block penetration |
Japanese straightening | Wait 1–3 months | Same reason, higher stakes |
Repeat acid-heat | Space it out | Over-cross-linking stiffens hair |
Repeated acid-heat over many months can over-cross-link the hair and make it feel stiff — at which point the only fix is growing it out. And whenever you do book a perm or straightening elsewhere, tell that stylist what you had done. A stylist who doesn't know can badly misjudge their formula.
An honest note on safety
We describe this treatment as formaldehyde-free because it is. We're careful not to describe it as risk-free, because no chemical service is.
Glyoxylic acid, the standard formaldehyde replacement, has drawn its own scrutiny — including case reports in 2024 of acute kidney injury linked to hair straightening products containing it. The reported cases involved leave-on exposure protocols quite different from a professional in-salon service, but we think you should know that the research is ongoing rather than settled.
What we can tell you plainly: no formaldehyde, no formaldehyde-releasing agents, and moderate iron temperatures. There is some odour during the service — less than a traditional keratin treatment, but present. We air the room between guests, and if it bothers you at any point, tell us and we'll open things up.
Getting it right for your hair
Hair varies enormously, and photographs tell us far more than a description does.
Send us a photo before you book. We'll tell you honestly whether this treatment suits your hair, what result you can realistically expect, how long it should last, and the exact price. If it isn't right for you, we'll say so and suggest what is.
No obligation to book, and no sales pressure. We're a private, appointment-only salon in Sapporo, and we'd rather have one guest who leaves happy than three who leave unsure.
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