Last updated: March 2026 — Written by the ORVOVA team, reviewed by our dermocosmetics advisor.
Keratin is the most-uttered word in hair salons. "Keratin" smoothing treatments, keratin "plumping" masks, shampoos "enriched with keratin". The term has become a universal marketing argument.
But how many people actually know what keratin is, how it works, and above all how to strengthen it effectively? Because spoiler: applying keratin to damaged hair doesn't "repair" anything in the biological sense. Real hair strengthening happens elsewhere — at the root, in your diet, in daily protection.
This article sets the record straight on keratin and gives you the strategies that genuinely work for stronger, more resilient, less brittle hair.
Contents
What exactly is keratin?
Keratin is a family of fibrous proteins — not a single molecule, but a group of more than 50 different proteins. They make up the main structural material of hair, nails, skin and even the surface layer of mucous membranes.
The structure of a hair
A hair is 85-90% keratin. Its structure resembles a fibre-optic cable:
- The medulla (core) — a central channel, sometimes hollow, which plays no major structural role
- The cortex (80% of the hair) — bundles of keratin fibres organised into macrofibrils and microfibrils, linked together by chemical bonds
- The cuticle (surface) — keratin scales stacked like roof tiles, protecting the cortex from external aggressors
The bonds that create strength
Hair's resilience doesn't come from keratin alone, but from the chemical bonds between keratin chains:
- Disulphide bonds (S-S) — the strongest. They link keratin chains to each other through sulphur atoms. These are the bonds that Brazilian blowouts and perms break and reform
- Hydrogen bonds — individually fragile but numerous. They break with water (which is why wet hair is more elastic) and reform as it dries
- Ionic (salt) bonds — sensitive to pH. Too alkaline a pH (>8) breaks them, an acidic pH (4-5) maintains them
A healthy hair can take a 100-gram load before breaking and stretch by 30% without damage. A damaged hair breaks at 50 grams and only stretches 10-15%. The difference: the integrity of those bonds.
[Image: Cross-section of a hair — medulla, cortex, cuticle and the 3 bond types]
What destroys keratin (and how to avoid it)
Heat: enemy number 1
The hairdryer, the straightener, the curling iron — every pass at high temperature breaks hydrogen bonds and, above 180°C, begins to denature the disulphide bonds irreversibly. At 230°C (a common setting on budget straighteners), the structure of the cortex is literally "cooked".
Practical solutions:
- Hairdryer on a warm setting, at least 20 cm from the hair
- Straightener/iron set to 180°C maximum (150°C for fine hair)
- Heat protectant every single time (it creates a film that absorbs part of the heat)
- Limit heat tools to 2-3 times a week maximum
Chemical treatments
Permanent colour and bleaching use ammonia (or its derivatives) to open the cuticle and hydrogen peroxide to alter the pigment. Every session damages the cuticle and reduces the cortex's resilience by 20 to 60% depending on the developer volume used.
Brazilian blowouts often contain formaldehyde (or molecules that release it under heat), which breaks the disulphide bonds to reform them in a straight configuration. The hair is smooth but structurally weakened.
Practical solutions:
- Space out colour appointments as much as possible (balayage limits root touch-ups)
- Choose demi-permanent colour (ammonia-free) for light coverage
- Avoid smoothing treatments containing formaldehyde
- After every chemical treatment: a deep reconstructing treatment for 4 to 6 weeks
Mechanical damage
Aggressive brushing on wet hair (when hydrogen bonds are broken and hair is at its most fragile), metal hair ties, styles pulled too tight, friction from a cotton pillowcase — all these daily micro-aggressions wear down the cuticle and expose the cortex.
Practical solutions:
- Detangle with a wide-tooth comb on damp (not soaking) hair, working from the ends up to the roots
- Use fabric or spiral hair ties (no metal)
- Switch to a silk or satin pillowcase (reduces friction by 40%)
- Never brush wet hair with a standard brush
[Image: Healthy cuticle (smooth scales) vs damaged cuticle (lifted, broken scales) under the microscope]
To round off your reading, discover how effective biotin is.
Topical care: what really strengthens
Hydrolysed keratin treatments
Hydrolysed keratin is keratin broken into small fragments (peptides) that can penetrate the hair cortex. Unlike intact keratin (a molecule far too large to get inside the hair), hydrolysed keratin:
- Temporarily fills the porous areas of the cortex
- Improves tensile strength by 10 to 20%
- Smooths the cuticle by filling the gaps between lifted scales
An important limitation: this is temporary filling, not repair. Hydrolysed keratin washes out over successive shampoos (3-8 washes). Hair needs re-treating regularly.
Oils: sealing, not repairing
Hair oils (argan, coconut, jojoba, avocado) don't act on keratin itself. They create a hydrophobic film around the hair that:
- Reduces moisture loss from the cortex
- Smooths lifted cuticles through surface tension
- Protects against friction (detangling, pillow rubbing)
Coconut oil is the only one shown to penetrate the cortex, thanks to its small molecular size (lauric acid). The others stay on the surface — which isn't useless, but is less effective for structural strengthening.
Acidic treatments (apple cider vinegar, acid rinses)
Cuticles close in an acidic environment and open in an alkaline one. An acid rinse (pH 4-5) after shampooing closes the cuticles back down, which:
- Increases shine (smooth cuticles = better light reflection)
- Reduces porosity and breakage
- Strengthens the ionic bonds between keratin chains
Apple cider vinegar (1 tablespoon in 500 mL of cold water) is the most accessible option. Commercial "cuticle sealer" products use the same principle at an optimised pH.
Strengthening at the root: the real long-term solution
Strengthening an existing hair is damage control. Real hair strengthening happens before the hair emerges from the scalp — in the follicular matrix, where keratin is synthesised.
Eating for keratin synthesis
Keratin is a protein. Synthesising it requires specific amino acids:
Cysteine and methionine (sulphur amino acids) — these are the building blocks of disulphide bonds. Sources: eggs, poultry, fish, broccoli, garlic, onions. Cysteine can also be synthesised from methionine, provided the cofactors (vitamin B6, folate, B12) are present.
Organic sulphur — sulphur is the third most abundant element in hair (after carbon and oxygen). Cruciferous vegetables (broccoli, cabbage, cauliflower), garlic and onions are the best dietary sources.
Glycine and proline — needed for the extracellular matrix that supports the follicle. Sources: bone broth, gelatine, collagen.
The essential minerals:
- Iron — carries oxygen to the follicular matrix (red meat, lentils, spinach)
- Zinc — a cofactor of protein synthesis (oysters, pumpkin seeds, beef)
- Silicon — involved in forming keratin and collagen (horsetail, nettle, wholegrains)
- Copper — needed for disulphide bonds and hair melanin (liver, dark chocolate, cashews)
The topical actives that strengthen from the root
Working directly on the scalp to stimulate the production of stronger, thicker hair is complementary to diet.
Rosemary at 3% applied topically stimulates scalp microcirculation, increasing the nutrient supply to the follicle. Better-fed hair is stronger hair from the root up.
Redensyl targets follicular stem cells, encouraging the production of hair in a full anagen phase — hair that has had time to develop a solid keratin structure rather than fine, miniaturised strands.
Anagain, derived from pea sprouts, stimulates dermal papilla cells to initiate complete new hair cycles.
The ORVOVA Roll-On Hair Growth Serum combines these actives in a daily topical treatment. The idea isn't to "glue keratin" onto existing hair — it's to create the conditions for every new hair that grows to be structurally stronger than the last.
[Image: The best foods for keratin synthesis — sources of sulphur, iron, zinc and protein]
For further reading, see our article on castor oil and hair growth.
The myths about keratin
"Keratin smoothing repairs hair"
False. "Keratin" smoothing uses formaldehyde (or similar molecules) to break and reform disulphide bonds in a straight configuration. The keratin in the formula is a marketing argument — the active agent is the formaldehyde, not the keratin. The result is smooth but structurally weakened hair.
"Eating gelatine makes hair grow"
Partly true. Gelatine is rich in glycine and proline, amino acids useful for the follicular matrix. But it contains neither cysteine nor methionine — the amino acids specifically needed for keratin. It's a useful supplement, not a complete solution.
"Dead hair can't be strengthened"
Technically true — visible hair is dead tissue, it can't "heal". But you can temporarily strengthen its structure with the right treatments (hydrolysed keratin, penetrating oils, acid rinses) and above all prevent future damage. The most effective strengthening happens at the root, for the hair that hasn't grown out yet.
"You have to trim the ends to strengthen hair"
Trimming the ends removes split ends and stops the split travelling up the shaft. That's prevention, not strengthening. A trimmed hair doesn't grow back "stronger" — but it breaks less, which gives the impression of growing faster.
The complete programme for stronger hair
The daily foundation
- A diet rich in protein and sulphur — eggs, fish, cruciferous vegetables, pulses
- Adequate hydration — 1.5 to 2 L of water a day
- Topical serum on the scalp — targeted actives (rosemary, Redensyl, Aminexil)
- Mechanical protection — silk pillowcase, gentle hair ties, careful detangling
The weekly treatments
- Hydrolysed keratin mask — 10-20 minutes, once a week
- Pre-shampoo coconut oil treatment — 30 minutes before washing (the only oil that penetrates the cortex)
- Acid rinse — diluted apple cider vinegar after the final rinse
The heat protection rules
- Heat protectant before every exposure to heat
- Straightener/iron temperature ≤ 180°C
- Hairdryer at a distance (20 cm) and on a warm setting
- A maximum of 2-3 heat-tool sessions a week
[Image: The complete hair-strengthening routine — daily habits and weekly treatments]
To dig deeper into this, see our guide to an anti-hair-loss hair routine.
Frequently asked questions
Do keratin supplements strengthen hair directly?
No. Keratin supplements are digested into individual amino acids by your digestive system, like any other protein. Your body then uses those amino acids to synthesise its own proteins — keratin included — according to its own priorities. That's why it's better to supplement the specific amino acids (cysteine, methionine) and cofactors (zinc, iron, B6) rather than "keratin" in capsule form.
How long before you see an improvement in hair quality?
Hair grows around 1 cm a month. To see a change in quality in the new hair (thicker, shinier, more resilient), allow 3 to 6 months of consistent care and an adapted diet. Topical treatments (keratin masks, oils) show an immediate but temporary effect on existing hair.
Does a Brazilian blowout damage hair permanently?
A Brazilian blowout breaks and reforms disulphide bonds, which weakens the keratin structure. The damage is permanent on the treated section of hair — it will never regain its original strength. But the new hair growing after the treatment is intact. That's why, after a smoothing treatment, the regrowth comes back in its natural texture.
Does hard water damage hair keratin?
Yes. The calcium and magnesium ions in hard water deposit on the cuticle, creating a mineral film that stiffens the hair, dulls shine and stops treatments penetrating. A limescale shower filter or an acid rinse after shampooing (diluted apple cider vinegar) neutralises the problem.
Are collagen and keratin the same thing?
No. Collagen and keratin are two distinct protein families with different structures and functions. Collagen is the structural protein of skin, tendons and connective tissue. Keratin is the protein of hair, nails and the epidermis. That said, the collagen in your scalp supports the hair follicle, so healthy collagen indirectly benefits your hair.
Do curly or coily hair types need more keratin?
Curly and coily hair has an elliptical cross-section (vs round for straight hair), which creates weak points along each twist. It's naturally more porous and more fragile, so more prone to breakage. Treatments enriched with hydrolysed keratin and penetrating oils are indeed more beneficial for these hair types.
