Keratin is the fibrous protein that makes up most of the hair, in the order of 90 to 95% of the fibre. It is produced by the hair follicle, in the scalp. Once the hair has emerged, the fibre is dead matter: it no longer produces keratin and cannot repair on its own what it loses. Heat, colouring, UV, salt and friction take a little away each time, and it is this cumulative loss that leaves hair dull, porous and brittle.
What exactly is keratin?
Keratin is a fibrous, insoluble protein, particularly rich in cystine, a sulphur-containing amino acid. That sulphur content is what makes it special: cystine molecules form disulphide bridges between them, very strong bonds that give hair its shape, its strength and its elasticity. Healthy hair can stretch by around 30% of its length when wet without breaking.
Within the hair, it is organised into two zones that do not play the same role.
- The cortex, at the centre, concentrates the bulk of the keratin and carries the pigments. It is what provides strength, elasticity and colour.
- The cuticle, on the surface, is made of keratin scales overlapping like roof tiles. When they lie flat, they reflect light and keep water inside the fibre.
The same family of proteins forms nails and the outer layer of skin.
Why does hair lose its keratin?
Because hair is dead matter: every assault removes protein with no biological mechanism to replace it. The damage adds up from top to bottom, which is why the ends are always more damaged than the roots.
| Aggressor | What it does to the fibre | Visible sign |
|---|---|---|
| Heat (hairdryer, irons above 180°C) | Weakens the bonds and creates micro-cracks in the cuticle | Rough feel, breakage |
| Colouring, bleaching, relaxing | Deliberately open the scales to act within the cortex | Porosity, colour bleeding out |
| UV, pollution, seawater, chlorine | Oxidise keratin and surface lipids | Dryness, washed-out tones |
| Friction (brushing, cotton pillowcases, hair ties) | Mechanically erode the scales | Frizz, split ends |
| Overly detergent surfactants | Strip away the natural protective film | A fibre that drinks water and dries too fast |
What are the signs of a keratin shortfall?
Seven signals come up again and again. They all reflect the same reality: an open cuticle and a depleted cortex.
- The fibre absorbs water very fast and dries just as fast
- Short broken hairs appear along the lengths, with no white bulb at the base
- The ends split
- The feel turns rough, what is known as the straw effect
- Frizz persists even in dry weather
- A wet hair pulled taut snaps instead of springing back
- Shine disappears, even on clean hair
Each sign and the corrective step that goes with it are covered in our article on the 10 signs of damaged hair. To get an objective read on how permeable your fibre is, try the porosity test.
How do you restore keratin in hair?
Only by supplying hydrolysed keratin from outside, meaning keratin broken into peptides small enough to cross the cuticle. Whole keratin is too bulky: it sits on the surface and rinses away. The effect is real but temporary, fading wash after wash, which makes regularity the single most important factor.
The precise mechanism, how to read the label and the limits of the exercise are set out in our article on hydrolysed keratin. If you are looking for an alternative without an animal-derived ingredient, the comparison is in hydrolysed keratin or plant keratin.
Three principles hold whatever product you choose.
- Regularity beats concentration. A weekly top-up does better than an overdosed treatment once a quarter.
- Protein and moisture go together. A fibre saturated with protein and short on humectants turns stiff and brittle: that is protein overload.
- Less damage is worth more than more care. Every blow-dry skipped is a treatment gained.
What routine maintains your keratin capital?
Four steps are enough, at different frequencies. The full method, with adjustments by hair type, is in our four-step hair routine.
- At every wash: the /RESET Shampoo lays down a first dose during cleansing.
- At every wash: the /RESTORE Conditioner closes the cuticle back down on mid-lengths and ends.
- Once or twice a week: the /REPAIR Mask delivers the most concentrated dose, 5 to 10 minutes on towel-dried hair.
- Every day: the leave-in /REVEAL Mist maintains the result between washes.
Give it four to six weeks before judging. Hair grows about a centimetre a month: what you are assessing is not new growth, it is the condition of the lengths already there.
Keratin and hair: the essentials
- Keratin accounts for around 90 to 95% of the hair fibre.
- Hair is dead matter: it never rebuilds on its own what it loses.
- Only hydrolysed keratin penetrates the fibre. Whole keratin stays on the surface.
- The effect lasts a few washes: this is upkeep, not permanent repair.
- Too much protein without moisture stiffens hair and makes it brittle.
- No product applied along the length acts on growth, which happens in the follicle.
Frequently asked questions about keratin
Is the keratin in hair products the same as the keratin in my hair?
It is the same family of proteins, but hydrolysed, meaning broken into smaller peptides. That reduced size is what allows it to enter the fibre, where whole keratin would simply sit on the surface.
Are keratin treatments only for very damaged hair?
No. Used preventively, they strengthen the fibre before damage sets in, which is useful if you colour your hair or use heat tools regularly. On healthy hair, go for light textures such as a shampoo and a leave-in.
Does a keratin treatment straighten hair like a Brazilian blowout?
No, and the confusion is common. A cosmetic product does not change the natural shape of hair: a curl stays a curl. So-called keratin straightening is a high-temperature technical service, belonging to an entirely different product category.
How often should keratin products be used?
Shampoo, conditioner and leave-in can be used at every wash. The mask goes on once or twice a week depending on the condition of the hair. On very sensitised hair, alternate with purely moisturising products to keep the balance.
Does keratin make hair grow?
No. Growth happens at the follicle, beneath the scalp, and a product applied along the length has no access to it. That said, a less brittle fibre holds on to its length better, which sometimes gives the impression of faster growth.
Is a keratin treatment vegan?
No. Keratin is a protein that only animals produce; there is no plant version of it. The keratin in our formulas comes from sheep's wool, an origin confirmed in writing by our manufacturer, who is the responsible person for the product under European regulation. Our products are therefore not vegan, and we will never present them as such.
Sources
- Robbins C. R., Chemical and Physical Behavior of Human Hair, 5th edition, Springer, 2012.
- Gavazzoni Dias M. F. R., "Hair Cosmetics: An Overview", International Journal of Trichology, 2015.
- Lee Y. et al., "Hair Shaft Damage from Heat and Drying Time of Hair Dryer", Annals of Dermatology, 2011.
Article written by the KERA NEXT editorial team from the cosmetology literature cited. It is not a substitute for medical advice. Individual results: the outcome may vary depending on the nature and condition of your hair.