Last updated: March 2026 — Written by the ORVOVA team, reviewed by our dermo-cosmetic advisor.
Keratin is the most spoken word in hair salons. "Keratin" straightening, "keratin-replenishing" masks, "keratin-enriched" shampoos. The term has become a universal marketing buzzword.
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, through nutrition, through daily protection.
This article sets the record straight on keratin and gives you strategies that actually work for stronger, more resilient, less breakage-prone hair.
What exactly is keratin?
Keratin is a family of fibrous proteins — not a single molecule, but a group of over 50 different proteins. They form the main structural material of hair, nails, skin, and even the superficial layer of mucous membranes.
Hair structure
A hair strand is 85-90% keratin. Its structure resembles a fiber optic cable:
- The medulla (core) — a central canal, sometimes hollow, that doesn't play a major structural role
- The cortex (80% of the hair) — bundles of keratin fibers organized into macrofibrils and microfibrils, linked together by chemical bonds
- The cuticle (surface) — keratin scales stacked like roof tiles, protecting the cortex from external damage
The bonds that create strength
Hair's resistance doesn't come from keratin alone, but from the chemical bonds between keratin chains:
- Disulfide bonds (S-S) — the strongest. They link keratin chains through sulfur atoms. These are the bonds that Brazilian straightening 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 when drying
- Ionic (salt) bonds — sensitive to pH. Too alkaline a pH (>8) breaks them, acidic pH (4-5) maintains them
Healthy hair can support a load of 100 grams before breaking and stretch 30% without damage. Damaged hair breaks at 50 grams and only stretches 10-15%. The difference: bond integrity.
[Image: Cross-section of a hair strand — medulla, cortex, cuticle and the 3 types of bonds]
What destroys keratin (and how to avoid it)
Heat: enemy number 1
The blow dryer, flat iron, curling iron — every pass at high temperature breaks hydrogen bonds and, above 180°C (356°F), begins to denature disulfide bonds irreversibly. At 230°C (446°F) — a common temperature on cheap flat irons — the cortex structure is literally "cooked."
Practical solutions:
- Blow dryer on warm (not hot) setting, at least 20 cm from hair
- Flat iron/curling iron set to 180°C max (150°C for fine hair)
- Heat protectant every time (creates a film that absorbs some of the heat)
- Limit heat tools to 2-3 times per week maximum
Chemical treatments
Permanent color and bleaching use ammonia (or derivatives) to open the cuticle and hydrogen peroxide to modify pigment. Each session damages the cuticle and reduces cortex resistance by 20 to 60% depending on the developer volume used.
Brazilian blowouts often contain formaldehyde (or molecules that release it with heat), which breaks disulfide bonds to reform them in a straight configuration. The hair is smooth but structurally weakened.
Practical solutions:
- Space out color sessions as much as possible (balayage technique to limit root touch-ups)
- Choose demi-permanent color (ammonia-free) for light coverage
- Avoid straightening treatments containing formaldehyde
- After every chemical treatment: deep reconstructive treatment for 4 to 6 weeks
Mechanical damage
Aggressive brushing on wet hair (when hydrogen bonds are broken and hair is most fragile), metal hair ties, too-tight hairstyles, cotton pillowcase friction — all these daily micro-aggressions wear down the cuticle and expose the cortex.
Practical solutions:
- Detangle with a wide-tooth comb on damp (not wet) hair, from tips to 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 regular brush
[Image: Healthy cuticle (smooth scales) vs damaged cuticle (lifted and broken scales) under microscope]
External treatments: what really strengthens
Hydrolyzed keratin treatments
Hydrolyzed keratin is keratin broken into small pieces (peptides) that can penetrate the hair cortex. Unlike intact keratin (too large a molecule to enter the hair), hydrolyzed keratin:
- Temporarily fills porous zones of the cortex
- Improves tensile strength by 10 to 20%
- Smooths the cuticle by filling gaps between lifted scales
Important limitation: this is a temporary fill, not a repair. Hydrolyzed keratin is washed out over successive shampoos (3-8 washes). Hair must be re-treated regularly.
Oils: seal, not repair
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 proven to penetrate the cortex thanks to its small molecular size (lauric acid). Others stay on the surface — which isn't useless, but less effective for structural strengthening.
Acidic treatments (apple cider vinegar, acid rinses)
Cuticles close in acidic conditions and open in alkaline ones. An acidic rinse (pH 4-5) after shampooing closes the cuticles, which:
- Increases shine (smooth cuticles = better light reflection)
- Reduces porosity and breakage
- Strengthens ionic bonds between keratin chains
Apple cider vinegar (1 tablespoon in 500 mL of cold water) is the most accessible option. Commercial "cuticle sealant" products use the same principle at an optimized pH.
Root-level strengthening: the real long-term solution
Strengthening existing hair is damage control. Real hair strengthening happens before the hair even emerges from the scalp — in the follicular matrix, where keratin is synthesized.
Diet for keratin synthesis
Keratin is a protein. Its synthesis requires specific amino acids:
Cysteine and methionine (sulfur-containing amino acids) — these are the building blocks of disulfide bonds. Sources: eggs, poultry, fish, broccoli, garlic, onions. Cysteine can also be synthesized from methionine, provided the cofactors (vitamin B6, folate, B12) are present.
Organic sulfur — sulfur 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, gelatin, collagen.
Essential minerals:
- Iron — transports oxygen to the follicular matrix (red meat, lentils, spinach)
- Zinc — cofactor in protein synthesis (oysters, pumpkin seeds, beef)
- Silicon — involved in keratin and collagen formation (horsetail, nettle, whole grains)
- Copper — needed for disulfide bonds and hair melanin (liver, dark chocolate, cashews)
Topical actives that strengthen from the root
Acting directly on the scalp to stimulate the production of stronger, thicker hair complements nutrition.
Rosemary at 3% applied topically stimulates scalp microcirculation, increasing nutrient supply to the follicle. Better-nourished hair means stronger hair from the root.
Redensyl targets follicular stem cells, promoting the production of hair in a complete anagen phase — hair that has had time to develop a solid keratin structure rather than thin, miniaturized strands.
Anagain, derived from peas, stimulates dermal papilla cells to initiate new complete hair cycles.
The ORVOVA Hair Regrowth Roll-On 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: Best foods for keratin synthesis — sources of sulfur, iron, zinc, and protein]
Common misconceptions about keratin
"Keratin straightening repairs hair"
False. Keratin straightening uses formaldehyde (or similar molecules) to break and reform disulfide bonds in a straight configuration. The keratin in the formula is a marketing argument — the active agent is formaldehyde, not keratin. The result is smooth but structurally weakened hair.
"Eating gelatin makes hair grow"
Partially true. Gelatin is rich in glycine and proline, amino acids useful for the follicular matrix. But it doesn't contain cysteine or 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 that can't "heal." But you can temporarily reinforce its structure with appropriate treatments (hydrolyzed keratin, penetrating oils, acid rinses) and most importantly prevent future damage. The most effective strengthening happens at the root, for hair that hasn't grown out yet.
"You need to trim the ends to strengthen hair"
Trimming removes split ends and prevents the split from traveling up the shaft. It's prevention, not strengthening. A trimmed hair doesn't grow "stronger" — but it breaks less, which gives the impression of growing faster.
The complete program for stronger hair
Daily foundation
- Protein and sulfur-rich diet — eggs, fish, cruciferous vegetables, legumes
- Adequate hydration — 1.5 to 2 L of water per day
- Topical serum on the scalp — targeted actives (rosemary, Redensyl, Aminexil)
- Mechanical protection — silk pillowcase, gentle hair ties, careful detangling
Weekly treatments
- Hydrolyzed keratin mask — 10-20 minutes, once per week
- Pre-shampoo coconut oil bath — 30 minutes before washing (the only oil that penetrates the cortex)
- Acid rinse — diluted apple cider vinegar after the final rinse
Heat protection rules
- Heat protectant before every heat exposure
- Flat iron/curling iron temperature no higher than 180°C
- Blow dryer at distance (20 cm) on warm setting
- Maximum 2-3 heat tool sessions per week
[Image: Complete hair strengthening routine — daily steps and weekly treatments]
Frequently asked questions
Do keratin supplements directly strengthen hair?
No. Keratin supplements are digested into individual amino acids by your digestive system, like any protein. Your body then uses those amino acids to synthesize its own proteins — including keratin — according to its priorities. That's why it's better to supplement specific amino acids (cysteine, methionine) and cofactors (zinc, iron, B6) rather than keratin capsules.
How long does it take to see hair quality improvement?
Hair grows about 1 cm per month. To observe a quality change in new hair (thicker, shinier, more resistant), expect 3 to 6 months of regular care and proper nutrition. External treatments (keratin masks, oils) show an immediate but temporary effect on existing hair.
Does Brazilian straightening permanently damage hair?
Brazilian straightening breaks and reforms disulfide bonds, weakening the keratin structure. The damage is permanent on the treated portion of hair — it will never regain its original strength. But new hair growing after treatment is intact. That's why regrowth returns to its natural texture.
Does hard water damage hair keratin?
Yes. Calcium and magnesium ions in hard water deposit on the cuticle, creating a mineral film that stiffens hair, dulls shine, and prevents treatments from penetrating. A shower filter or an acid rinse after shampooing (diluted apple cider vinegar) neutralizes this 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. However, scalp collagen supports the hair follicle, so good collagen health indirectly benefits hair.
Do curly or coily hair types need more keratin?
Curly and coily hair has an elliptical cross-section (vs. round for straight hair), creating weak points along the twists. It's naturally more porous and fragile, thus more prone to breakage. Treatments enriched with hydrolyzed keratin and penetrating oils are indeed more beneficial for these hair types.
