Keratin & Hair: Treatment, Care, Smoothing & Risks (2026)

Keratin is everywhere: in shampoo adverts, in the chat at the salon, on the ingredient list of your mask. But what is really behind it, what does a treatment actually do, and when does it become tricky? This guide (as of 2026) explains the protein, gives an honest comparison of treatment, salon blow-out and smoothing, and shows what you need to watch out for when it comes to formaldehyde.

What is keratin? The protein in your hair, simply explained

Keratin is a fibre-forming structural protein and the main building block of hair, nails and the outermost layer of skin. Depending on the source and hair type, human hair is made up of roughly 65 to 95 per cent keratin, with a figure of around 90 per cent often quoted (keratin.com). The rest is water, lipids and traces of minerals and melanin.

Keratin is built from amino acids. The key one is the sulphur-containing amino acid cysteine: it forms what are known as disulphide bridges between the protein chains. The denser this network of bridges, the stronger and more resilient the hair (MedLexi.de, medi-karriere.de). In mammals it occurs as so-called alpha-keratin, whose helical structures give the hair its elasticity.

Where in the hair does the keratin sit?

Keratin sits in two parts of the hair. The cortex (the cortical layer) makes up 80 to 90 per cent of the hair’s volume and provides the mechanical strength. The cuticle (the scale layer) is the outer sheath of flat, overlapping keratin scales that protects the cortex (ScienceDirect). It is this scale layer that most keratin care products work on.

Natural and added keratin: where it comes from

Your body makes its own keratin. The keratin in cosmetics is usually hydrolysed keratin (INCI: Hydrolyzed Keratin): hydrolysis splits the long protein chains into smaller fragments so they can bind to the hair. It is traditionally obtained from sheep’s wool, feathers or animal horn (INCI Beauty, keratin-info.de). It is therefore of animal origin.

If you prefer vegan options, there are “keratin-like” alternatives: phytokeratin based on hydrolysed wheat or soy protein (INCI: Hydrolyzed Wheat Protein). It is structurally similar to keratin and conditions comparably, but it is not identical (myrto-naturalcosmetics.de, Jean&Len). Do not confuse keratin with collagen: collagen sits in the skin around the follicle, not in the hair fibre itself (bubsnaturals.com).

Keratin treatment, keratin care or keratin smoothing: the difference

A keratin treatment can mean three different things, and that is exactly what often gets confused. Anyone searching for “keratin treatment” usually means one of these three variants:

So many users are only after a conditioning mask, while others want strong smoothing. The nourishing keratin treatment repairs the look and adds shine, the salon treatment or express blow-out smooths lightly, and chemical keratin smoothing relaxes the hair’s curl long term (numihair.com, clinikally.com). Only the third variant is a genuine chemical process.

Chemical smoothing in the salon works like this: wash the hair, apply the keratin solution and leave it on for about 20 minutes, blow-dry with a round brush and then seal it strand by strand with a flat iron at around 200 to 230 degrees (keratin.pro). Total time 2 to 4 hours. Many people also know this variant as the “Brazilian Blowout” or “Brazilian keratin treatment”.

Guide values. Sources: headmasters-beauty.de, keratin-info.de, perfecthair.ch, numihair.com, clinikally.com.

An important point on durability: with good care, a classic keratin treatment lasts 3 to 6 months, while a “Brazilian Blowout” tends to last 8 to 12 weeks, that is 2 to 3 months (clinikally.com, salon833.com). Unlike a perm, there is no harsh regrowth line, the result grows out gently.

Is keratin good for your hair? An honest look at the benefits and effects

Is keratin good for your hair? For the surface, yes: hydrolysed keratin fills in microscopic gaps in the scale layer, reduces frizz, adds shine and makes the hair easier to comb. It is a cosmetic effect, not regrowth and not a repair of the hair root. Think of keratin as a temporary filler for cracks, not a cure.

The mechanism is well studied. According to the study by Malinauskyte et al. (2020, Int. J. Cosmet. Sci.), small keratin fragments (221 and 2,577 daltons) penetrate deep into the cortex, while large fragments (75,440 daltons) form a protective film on the cuticle. Fan et al. (2025, Molecules) further showed that treated hair retained its tensile strength after UV exposure, whereas untreated hair lost 14.32 per cent.

Those who benefit most are people with frizzy, curly, coarse and chemically stressed or bleached hair: less frizz, more shine, and in some cases more than 50 per cent shorter blow-drying time (Healthline). Keratin is less suitable for fine, already straight hair, which it can weigh down and make look flat (Healthline). Anyone who wants to keep their curls should avoid chemical smoothing, as it dissolves the curl pattern.

The honest limit: the effect is temporary and superficial. Hair is a dead keratin fibre, not living tissue. Keratin improves the appearance, but it does not repair the fibre biologically. After a few washes (a treatment) or 2 to 5 months (smoothing), the effect has faded and the treatment is repeated.

Risks and downsides of keratin smoothing: the formaldehyde problem

The biggest risk of keratin smoothing is formaldehyde. Many smoothing products contain methylene glycol or other formaldehyde releasers that release formaldehyde when heated. The IARC classifies formaldehyde as carcinogenic to humans (Group 1, Monograph 100F, 2012); the European ECHA classifies it as a suspected carcinogen (Carc. 1B, since 2016). Both classifications are grounds for clear caution.

In the EU, free formaldehyde has been banned in cosmetics since May 2019 (Annex II of Regulation (EC) No 1223/2009). Formaldehyde releasers remain permitted within limits, but they are regulated. Since 31 July 2024, products that release more than 10 ppm of formaldehyde must carry the warning “releases formaldehyde” (Regulation (EU) 2022/1181). So it is not enough to simply look for the word formaldehyde on the label.

Germany’s Federal Institute for Risk Assessment (BfR) warned back in 2010 (press release 16/2010): hair-smoothing products that were tested contained 1.6 to 2.0 per cent free formaldehyde, well above the limit of 0.2 per cent. The BfR explicitly advised both consumers and hairdressers against using them. OSHA measured 10 ppm in a salon during blow-drying, five times the short-term limit (OSHA).

In the USA, the FDA proposed a ban on formaldehyde-containing hair straighteners in October 2023 and is sticking with it; the exact timetable, however, is still pending, with the deadline pushed back several times (most recently the end of 2025, CNN January 2026). As of 2026, the ban has therefore been announced but is not yet in force.

Heat damage, hair breakage and protein overload

Besides formaldehyde, keratin smoothing carries other risks. A flat iron at 200 to 230 degrees can damage the scale layer, especially on fine or already damaged hair. This leads to hair breakage (the fibre snaps), not to true hair loss from the root. Treatments that are too frequent or too concentrated can trigger a protein overload: the hair becomes stiff and brittle despite the care.

Does keratin make you lose hair? High-quality treatments carried out with suitable products do not damage the hair permanently. Genuine, lasting hair loss caused by keratin is not documented (numihair.com, belgraviacentre.com). In rare individual cases, the chemical and thermal stress can trigger a temporary telogen effluvium, which is reversible.

Sources: BfR, OSHA, EU Cosmetics Regulation, perfecthair.ch, headmasters-beauty.de.

Keratin during pregnancy and common safety questions

During pregnancy and breastfeeding, expert bodies advise avoiding keratin smoothing that contains or releases formaldehyde. The basis for this is not proven harm in humans, but the precautionary principle: in high doses, formaldehyde is reprotoxic (animal data, PubMed PMID 11572272). There are no clinical studies specifically on keratin during pregnancy.

Nourishing, formaldehyde-free keratin treatments are considered less problematic, but they should be discussed with the doctor looking after you. Bear in mind: even products marketed as “formaldehyde-free” can contain releasers. So do not base your decision on the packaging alone. Formaldehyde is also a known contact allergen and can irritate the scalp, eyes and airways.

Caring for hair with keratin: before and after the treatment

Keratin-treated hair needs sulphate-free and salt-free care. In the first 48 to 72 hours after smoothing, you should not wash the hair, not tie it up and not use a hair tie or clip, otherwise marks will stay visible in the fresh keratin seal (perfecthair.ch, keratin-info.de). Only after that does the full hold set in.

Why sulphate-free and salt-free? Sulphates are aggressive surfactants that quickly wash out the keratin seal and shorten the treatment; salt works in a similar way (frisurenmachen.de, headmasters-beauty.de). Wash 2 to 3 times a week rather than daily, as that extends the durability. Chlorinated and salt water from a pool or the sea shorten it considerably, so protect your hair or avoid them.

Sources: frisurenmachen.de, headmasters-beauty.de.

Do keratin shampoos and treatments from the chemist do anything? Realistically, yes, as ongoing care. Their keratin content is much lower and the sealing step with a flat iron is missing, so there is no lasting smoothing effect, but there is shine and protection against hair breakage (dm.de, deinfriseur.de). A top-up of the salon smoothing is usually due every 4 to 6 months and costs around £150 to £200.

Can you do keratin at home yourself? Conditioning treatments, yes, no problem. DIY smoothing kits exist too, with an effect lasting 2 to 4 months, but a weaker result than in the salon (Refinery29). Even, safe heat is harder to control at home, and the formaldehyde-free claim is hard to verify. For frizzy or coarse hair, a professional salon is the safer choice.

When keratin does not help: a damaged surface or genuine hair loss?

Keratin improves the look of the hair fibre, but it cannot stop thinning hair or hair loss. The reason: hair loss originates at the hair root, not at the surface. Keratin helps with frizz, dryness, split ends and hair breakage caused by external damage. It does not help with declining hair density, a widening parting or a receding hairline.

A simplified way to tell them apart: if a hair snaps off without a thickening at the end, it is hair breakage, where keratin can help. If a hair comes out of the root with a small bulb-shaped knot (the bulbus), the issue is the amount of hair, not the fibre. This does not replace a proper diagnosis, it is only a first orientation.

If, despite good care and regular keratin treatments, you notice that there is less hair overall or that your parting is visibly getting wider, you should have the cause assessed rather than just treating the surface. A free hair analysis can help work out whether care is enough or whether there is genuine hair loss. You can also find background information in the overview of the causes of hair loss.

FAQ: keratin and hair

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