Does keratin make hair grow? What you really need to know

The question "Does keratin make hair grow?" is frequently asked by people dealing with brittle, damaged hair or hair that struggles to gain length. Between marketing promises, enriched hair care products, and dietary supplements, keratin is often presented as an essential active ingredient for hair growth. However, its true role deserves to be clarified in light of the biological mechanisms of hair growth.

Understanding whether keratin makes hair grow requires distinguishing growth in the strict sense—which takes place at the hair follicle level—from the quality of the visible hair fiber. In other words, keratin does not act where the hair is born, but where it becomes fragile. It is precisely this nuance that explains why keratin is both indispensable for hair health, without being a direct trigger for regrowth.

Before asking whether keratin makes hair grow, we must understand what it is and the role it plays in the hair fiber, as that is where its true value lies.

Keratin is a fibrous protein produced by the body. It makes up hair, nails, and the surface layer of the epidermis, and accounts for the vast majority of the hair's dry mass. It is the basic material for hair health.

Its distinctiveness lies in its richness in sulfur-containing amino acids, primarily cysteine. Two neighboring cysteines unite via a disulfide bridge, a very stable bond. Multiplied by the thousands, these bridges give hair its strength, shape, and structure.

Hair consists of three layers:

• The cuticle, made of overlapping scales, acts as a barrier against external damage.
• The cortex concentrates most of the mass and mechanical resistance.
• The medulla, at the center, is often absent in fine hair.

Keratin forms the framework of the cortex. UV rays, heat from styling tools, coloring, and oxidative stress gradually break some of its bonds. The hair fiber becomes porous, dull, and brittle. Hair shortens, not because it grows less, but because it breaks more quickly.

In other words, keratin does not determine the rate of hair growth. It conditions the hair's ability to reach and then maintain its length.

Natural keratin is produced by keratinocytes in the bulb during the growth phase. Once it emerges from the scalp, the hair is an inert fiber that does not replenish itself.

Supplemental keratin follows two distinct paths. Keratin treatments deposit protein fragments onto the surface of the fiber: their action is cosmetic, and their efficacy depends heavily on the formula and frequency of use. The oral route relates to nutrition: ingested keratin is digested into peptides and amino acids, available to the entire body.

Keratin is often presented as a growth accelerator, but the mechanisms of hair growth tell a more nuanced story: to separate fact from fiction, we must look at where hair is born and what determines its rhythm.

Growth follows the hair growth cycle, in three phases:

• The anagen phase, of active growth, lasts from two to seven years and affects about 85% of hairs.
• The catagen phase, a transition phase, lasts a few weeks.
• The telogen phase, a resting phase, lasts about three months before the hair falls out to make room for the next one.

During the anagen phase, hair advances about 0.35 mm per day, or one centimeter per month. This speed depends primarily on genetics, hormonal status, and nutritional state. The daily loss of 50 to 100 hairs is part of this normal renewal.

Keratin is the product of growth, not its driver. The rhythm is set by the cells in the bulb matrix, the dermal papilla that guides them, scalp microcirculation, and hormonal signals. None of these mechanisms are controlled by the amount of keratin present in the fiber.

Therefore, no data suggests that keratin accelerates hair growth. Answering "yes" to the question "does keratin make hair grow?" would be inaccurate. Answering "no" would be incomplete.

A 30 cm hair is over two years old: its ends have endured hundreds of brushings, shampoos, and dryings. If the fiber wears out faster than it grows, the length stagnates.

A well-structured fiber resists pulling and friction better. Each centimeter gained is preserved: it is this preserved hair length that we perceive as faster growth.

While keratin does not dictate the speed of growth, it directly influences what we see of hair growth: the length retained, the appearance of the fiber, and its quality at each new growth phase.

Breakage is concentrated on the lengths and ends, where the cuticle is most worn. When the cuticles are lifted, the cortex is exposed and splits. Keratin treatments temporarily fill these porous areas, which reduces friction and limits split ends. Less hair breakage means more hair length retained.

A homogeneous fiber reflects light better and maintains a regular diameter down to the ends. The hair appears thicker. The number of hairs has not changed: it is their quality that alters the perception of density and gives the image of strong hair.

The quality of the fiber is determined during the anagen phase, when the bulb produces keratin. A bulb properly supplied with amino acids, vitamins, and minerals produces a higher-quality hair. This is where nutrition takes over from surface treatments, without altering the rhythm of the hair growth cycle.

Does keratin make hair grow differently depending on whether it is applied or ingested? Neither method acts on the speed of growth, but they do not intervene in the same place, nor on the same timescale.

Shampoos, masks, and serums generally contain hydrolyzed keratin, broken down into small enough fragments to adhere to the cuticle. The result is rapid: a smoother feel, increased shine, easier detangling, and better hold for damaged hair.

These treatments help to strengthen hair on the surface, but their effect fades with subsequent washes and does not reach the follicle. To get the best out of them, see our guide to keratin hair treatments. So-called "keratin" straightening treatments follow a different logic: they reshape the fiber using heat and chemical agents, and can sensitize it if repeated.

A keratin dietary supplement does not deposit keratin into the hair. The protein is digested, and its amino acids (cysteine, methionine, and serine) join the body's resources. Its quality depends on the degree of hydrolysis, which conditions digestibility, and the purity of the raw material.

Clinical data remain limited. A randomized, double-blind, placebo-controlled trial (Beer et al., 2014) followed 50 women for 90 days with solubilized keratin combined with vitamins and minerals. It observed a favorable evolution of several hair parameters. These results concern a specific preparation. Furthermore, keratin does not have any authorized health claims in the European Union.

This is why high-quality formulas combine it with nutrients that have a recognized role. Biocyte, which introduced oral keratin in 2009, built Kératine Forte on this principle: 500 mg of hydrolyzed keratin, sulfur-containing amino acids, B-group vitamins, and zinc, which contributes to the maintenance of normal hair. All formulas are presented in our selection of keratin dietary supplements.

Topical treatments are suitable for hair sensitized by heat, coloring, friction, or hard water. Their benefit is immediate and cosmetic.

The nutritional approach is better suited to people whose hair length stagnates despite normal growth, or who are going through a period of increased needs. Both complement each other: nutrition concerns hair in the formation stage, while treatment concerns hair that is already visible.

The production of keratin by the hair bulb mobilizes vitamins, minerals, and amino acids, several of which have a recognized role in maintaining normal hair: it is their combination that gives meaning to a hair formula.

Biotin, or vitamin B8, contributes to the maintenance of normal hair and normal energy-yielding metabolism. As a coenzyme for amino acid metabolism, it is present in almost all hair formulas, alone or in combination, as in our biotin dietary supplements.

Two nuances are worth knowing. First, studies on biotin for hair mainly concern people with insufficient status; for others, data are rare (Patel et al., 2017). Second, high doses of biotin can interfere with certain biological tests, especially thyroid tests: it is best to mention it before a blood test.

Vitamin B6 contributes to the normal synthesis of cysteine, the key amino acid in keratin. Vitamins B3 and B5 contribute to normal energy-yielding metabolism, essential for matrix cells, which are among the most active in the body.

Zinc contributes to the maintenance of normal hair, normal protein synthesis, and the process of cell division. Selenium also contributes to the maintenance of normal hair, and copper to normal hair pigmentation.

Iron contributes to normal oxygen transport and cell division. Literature focuses on the iron status of women who experience diffuse hair loss (Almohanna et al., 2019). Its assessment, however, requires a blood test, and iron intake should be considered with a healthcare professional.

Cysteine and methionine are the direct building blocks for disulfide bonds. Diet provides them through eggs, fish, meat, legumes, and dairy products.

Collagen is not part of the hair's composition, but it structures the dermis in which the follicle is anchored. Keratin concerns the fiber, while collagen concerns its environment: a role detailed in our article on collagen and hair.

Whether of marine or bovine origin, collagen is judged by its degree of hydrolysis and purity. Vitamin C, which contributes to normal collagen formation for the normal function of the skin, often accompanies it. This global look at hair health, from the fiber to the scalp, is at the heart of Biocyte’s nutricosmetic approach.

The timeframe depends on what you are looking to observe: the appearance of the fiber can change in a few days, whereas length and perceived density follow the slow rhythm of the hair cycle.

With a keratin treatment, the difference is noticeable from the first application: smoother, shinier, and easier-to-detangle fiber. The effect lasts for a few washes and does not change hair growth.

A nutritional approach follows the rhythm of the hair cycle. Hair formed during intake takes several weeks to emerge, then advances by one centimeter per month. Count on at least three months of regular use to judge regrowth, and six months for an assessment of hair length and the number of broken hairs. Regularity matters more than dosage.

Quality hair fiber is not always enough: when hair loss or slow growth originates from the hair cycle itself, other factors come into play that are useful to know how to recognize.

Physiological hormonal variations alter the hair cycle, regardless of the quality of the fiber. After childbirth, the synchronization of cycles frequently causes marked hair loss between the second and fourth month. Stopping hormonal contraception or the menopause period have comparable effects. In the event of pregnancy or breastfeeding, it is important to seek advice from a healthcare professional before any supplementation.

Insufficient intake of proteins, iron, zinc, or vitamins also limits the production of quality hair. This is common during very restrictive diets. In this case, it is your diet as a whole that needs to be reviewed. Once intake is rebalanced, an anti-hair loss food supplement combining keratin, zinc, and biotin can complement the approach, as zinc and biotin contribute to the maintenance of normal hair.

Finally, a period of intense and prolonged stress can cause many hairs to shift into the telogen phase simultaneously. The hair loss becomes visible two to three months later, often once the episode has passed. Finding a balanced lifestyle and sleep rhythm is then part of the process, just as much as sleep and stress support.

Sudden hair loss, localized in patches, accompanied by itching or redness, or which continues beyond three months justifies medical advice. A doctor or dermatologist will be able to prescribe a blood test and identify the origin of the hair loss. The pharmacist remains a primary point of contact to guide the approach.

• Beer C, Wood S, Veghte RH. A clinical trial to investigate the effect of Cynatine HNS on hair and nail parameters. ScientificWorldJournal. 2014;2014:641723. Randomized, double-blind, placebo-controlled trial, 50 women, 90 days.
• Almohanna HM, Ahmed AA, Tsatalis JP, Tosti A. The role of vitamins and minerals in hair loss: a review. Dermatology and Therapy. 2019;9(1):51-70.
• Patel DP, Swink SM, Castelo-Soccio L. A review of the use of biotin for hair loss. Skin Appendage Disorders. 2017;3(3):166-169.
• Guo EL, Katta R. Diet and hair loss: effects of nutrient deficiency and supplement use. Dermatology Practical & Conceptual. 2017;7(1):1-10.
• Paus R, Cotsarelis G. The biology of hair follicles. New England Journal of Medicine. 1999;341(7):491-497.
• Robbins CR. Chemical and Physical Behavior of Human Hair. 5th ed. Springer, 2012.
• Gavazzoni Dias MF. Hair cosmetics: an overview. International Journal of Trichology. 2015;7(1):2-15.
• Regulation (EU) No 432/2012 establishing the list of authorized health claims (biotin, zinc, selenium, copper, vitamins B6, B3, B5, C, iron).