Keratin treatment: what it does and what to ask

What a keratin treatment is

A keratin treatment is a semi permanent smoothing service that seals your hair from the outside. It is emphatically not repair from within, however often it is sold that way.

Keratin is a fibrous protein that builds your hair, your skin and your nails. By dry weight a hair is roughly sixty five to ninety five percent protein, with the remainder mostly water and lipids.

Which means your hair is already full of keratin. What a treatment adds is a layer around it, not a top up inside it.

Dermatologist Nika Finelt describes the process plainly as a styling procedure: a cream is brushed through the hair, which is then blow dried and flat ironed. That sequence is the entire mechanism.

The confusion lives in the name. The word keratin suggests repair, while in practice the treatment is a coating.

How the treatment really works

The heat does the work, not the protein. Without a flat iron nothing of a keratin treatment remains.

The product contains hydrolysed keratin plus a compound from the aldehyde family acting as a linker. At high temperature that linker forms bridges between the applied keratin and the proteins in your own hair.

What you are left with is a protective film that lies the cuticle flat. A smooth cuticle reflects light more evenly, which is exactly why the hair looks shinier.

Less frizz comes from the same effect. Frizz happens when raised scales pull moisture out of the air, and a sealed shaft does that far less.

So it is a cosmetic effect with a chemical anchor. Once the film wears off, your hair behaves exactly as it did before.

Which hair type it works on

The frizzier and less manageable your hair, the bigger the difference. On fine straight hair the gain is so small that the investment rarely pays off.

• Coarse and strongly curly hair: the largest visible difference, with substantially less drying time.
• Dry, frizzy hair that reacts badly to humidity: this is the core of what the treatment is for.
• Thick, coarse hair that takes twenty minutes of styling each morning: that time drops noticeably.
• Wavy hair you already wear straight: a good candidate, because you save heat rather than adding it.
• Fine, straight hair: little to gain, and the film can leave it heavy and flat.

One point rarely in the brochure: if you like your curls, do not do this. A keratin treatment removes movement, and that is the goal rather than a side effect.

Badly damaged or freshly bleached hair calls for restraint. Never combine a lightening service and a smoothing treatment in the same week.

Formaldehyde and the European rules

In the European Union formaldehyde may no longer be used in cosmetics. That ban dates from 2019, after the substance was classified as a category 1B carcinogen under European rules and therefore fell automatically under the cosmetics prohibition.

Phrase that precisely though. There is no law banning keratin treatments as such; there is a general ban on the ingrediënt that happens to cover them.

That the ban arrived is not surprising. The International Agency for Research on Cancer classifies formaldehyde as group 1, carcinogenic to humans, with nasopharyngeal cancer as the best supported outcome.

Outside Europe the picture differs. The American FDA proposed a ban on formaldehyde in smoothing products in October 2023, but that rule has slipped year after year and has still not taken effect.

Why this matters if you live in the Netherlands: products you order online from abroad sit outside the oversight a salon does have. That is where the real exposure sits, not in what a professional uses in a European salon.

There is also a reason to read labels sceptically. Products marked formaldehyde free have on testing been found to contain methylene glycol, formaldehyde dissolved in water, which releases formaldehyde again when heated.

Glyoxylic acid and formaldehyde free formulas

Most modern formulas work with glyoxylic acid or similar linkers. They are not formaldehyde, but they are not automatically beyond question either.

The chemistry is related: an aldehyde group that bonds with the amino groups in your hair protein under heat. The end result on your hair therefore feels comparable.

Since 2024, however, reports of acute kidney injury after glyoxylic acid smoothing treatments have been accumulating. The New England Journal of Medicine described a patiënt with three separate episodes, each directly after such a treatment, and a medical toxicology service published a series of thirteen patients in 2025.

The suspected mechanism is the conversion of glyoxylic acid into oxalate, which can form crystals in the kidney. The French agency ANSES confirmed the alert in early 2025 and called for a European assessment.

It matters to keep this in proportion. These are case reports rather than an epidemiologically established risk for the average user, and glyoxylic acid is currently neither banned nor restricted in Europe.

The practical conclusion is simple: ask which product is used and which linker it runs on. A salon that cannot answer that is not the right place for this treatment.

What the research says about risk

The most cited research is not about keratin but about hair straightening products in general. Its findings deserve an honest, undramatised reading.

The American Sister Study followed over thirty three thousand women. In 2022, in the Journal of the National Cancer Institute, the researchers reported that women who had ever used straightening products had a raised chance of uterine cancer, with a hazard ratio of 1.80, rising to 2.55 for use more than four times a year.

Those numbers sound large, but they describe a relative risk for a condition that is rare in absolute terms. Without that nuance the finding reads as more alarming than the data justify.

An earlier publication from the same study, in the International Journal of Cancer in 2019, found roughly thirty percent higher breast cancer risk among women who chemically straightened every five to eight weeks. That is a different paper with a different endpoint, and the two are often confused.

The strongest signals come from the trade rather than the client, incidentally. Measurements by the American labour inspectorate OSHA found formaldehyde concentrations in salons reaching ten parts per million during blow drying, five times the short term exposure limit that same agency applies.

Ventilation is therefore not a detail. For someone having the treatment twice a year the risk picture differs fundamentally from that of a stylist performing it weekly.

How a keratin treatment goes

Count on two to three hours, depending on your hair length and thickness. Below is the sequence a keratin treatment follows.

1. Assessing your hair type, the damage and whether it has recently been coloured or lightened.
2. Washing with a clarifying shampoo that fully removes styling product and mineral residue, so the cuticle is open.
3. Blow drying to roughly eighty percent, since a soaking shaft takes the product unevenly.
4. Applying the liquid keratin in thin sections, away from the scalp and evenly along the lengths.
5. Letting it process, typically twenty to thirty minutes, in a well ventilated room.
6. Drying completely until no moisture is left in the hair.
7. Working section by section with the flat iron at the temperature the product specifies, usually several passes per strand.
8. Cooling and, depending on the brand, rinsing out or leaving it in for a few days.

The flat iron stage is where the treatment is locked in and simultaneously where fumes are released. Open windows and proper extraction belong here as standard.

How long the result lasts

Count on two to six months, with three to four as the working average. Wash frequency shifts that more than any other factor.

Washing daily can cut the effect back to a few weeks. Washing twice a week often keeps the result at strength for months.

Unlike permanent colour there is no hard regrowth line. The treatment fades gradually and your hair returns to its original behaviour without a visible border.

An honest caveat: nearly all hard figures on longevity come from manufacturers and salons. Independent research measuring this does not exist, so treat any timescale as an estimate.

Advantages and drawbacks

The gain is time and humidity resistance, the cost is money, movement and chemical exposure. Both sides belong in the same decision.

What you get

• Substantially less frizzy hair, including in humid weather.
• Noticeably shorter drying time, often halved on thick hair.
• Visibly shinier and smoother hair thanks to the closed cuticle.
• Less daily heat required, which saves damage over time.

What it costs

• A considerable expense that returns every three to four months.
• Loss of natural curl and movement, which cannot be undone before it washes out.
• Chemical exposure during the service, so good ventilation is a condition.
• On fine hair, the risk of a flat and heavy result.

Doing a keratin treatment at home

It is possible, but the risks of a keratin treatment at home do not sit in the technique. They sit in the ventilation and in the temperature of your flat iron.

The linker only releases under heat, and that is precisely the moment you fill your own bathroom with vapour. A small, poorly ventilated room is the worst possible place for that step.

On top of that, consumer straighteners often fail to hold their set temperature. Too cool and the film does not set, too hot and you damage the shaft permanently.

The third problem is dosage. Too much product leaves flat, greasy feeling hair, and that is not easily corrected by washing.

If you do it yourself anyway: ventilate heavily, wear gloves, keep the product away from your scalp and stick strictly to the specified temperature.

Shampoo and care after the treatment

Wait to wash for as long as the brand specifies, usually forty eight to seventy two hours. During that window no elastics, no clips and no tucking behind the ears.

After that the shampoo is the important choice. Salons recommend sulphate free as standard, though the evidence that sulphates specifically strip a keratin treatment is thin.

Better supported is the pH. The treatment sets the cuticle in a slightly acidic state, and an alkaline shampoo opens it again, which makes the effect fade faster.

In practice that comes to the same thing: a mild, slightly acidic shampoo without harsh cleansers, followed by conditioner. Salt water and chlorine accelerate the wash out considerably.

And contradictory as it sounds, you still need heat protection. The film protects against moisture, not against a straightener at two hundred degrees.

More on daily routines under hair care.

Pregnancy and breastfeeding

The advice is caution, and that is a precautionary position rather than an official ban. No health authority guideline exists that deals specifically with keratin treatments during pregnancy.

The reason for that caution is missing data. There is simply no research on exposure in pregnant users, and where inhaling vapour is involved that is reason enough not to seek the risk out.

If you want a treatment anyway: discuss it with your midwife or doctor first. Then choose an explicitly formaldehyde free formula and make sure the room has genuine ventilation.

What a keratin treatment costs

With Hanna Valiullina a keratin treatment starts at a hundred and ninety euro. Nanoplasty starts at two hundred and ten euro and a full restoration with botox at two hundred and forty.

Those amounts include the home visit within the service area. The final price depends on your hair length and thickness, since those decide product use and time.

In the Dutch market rates run roughly from a hundred and fifty euro to well over three hundred. Extremely low prices are a signal, because there is no cheap way to deliver three hours of work and professional product.

Budget three to four treatments a year to keep the effect continuous. That makes it one of the more expensive maintenance choices in hair care.

Keratin treatments at your home

Hanna Valiullina performs keratin treatments at your home in Papendrecht and the surrounding area. You need a chair, a socket and a room you can ventilate properly.

Every treatment starts with the question of whether your hair is ready for it. Freshly bleached or badly damaged hair gets a different approach first, and sometimes the honest answer is that a repair treatment delivers more.

Which product is used and what it runs on is something you hear before you say yes. See the options under services or read how cutting and colouring fit around it in the article on haircuts.

For an appointment or advice on what your hair can take, get in touch.

Frequently asked questions about keratin treatments

The essentials

A keratin treatment repairs nothing, it seals. The film makes your hair smoother, shinier and less frizzy, and disappears again within two to six months.

Formaldehyde has been banned as a cosmetic ingrediënt in Europe since 2019, so that old risk no longer applies here. The newer glyoxylic acid formulas raise questions of their own, and those are not yet answered.

So always ask which product is used and make sure the room is well ventilated during the ironing. That is the one precaution that stays sensible in every scenario.