Keratin, a natural protein for damaged hair

It represents up to 90 to 95% of the mass of the hair fiber, yet few people truly know what it is. Keratin protein forms the framework of the hair: it gives it its hold, its flexibility, and its ability to reflect light. Repeated coloring, straightening, curling irons, summer sun: each of these exposures alters this architecture, and the hair shows it quickly.

Understanding how the body makes keratin, why it gets damaged, and what is realistic to expect from a treatment or a keratin food supplement is the key to building a coherent routine rather than just accumulating products.

Before talking about hair care or supplements, it is necessary to understand what keratin protein really is: its composition, its different forms, and the tissues where the body produces it.

Keratin belongs to the family of fibrous proteins. Unlike globular proteins, which perform enzymatic or transport functions, it plays an essentially structural role. Its chains coil into spirals and then associate into increasingly thick filaments, until they form a true fiber.

Its chemical signature lies in its richness in cysteine, a sulfur-containing amino acid. The sulfur atoms of two neighboring cysteines bond together to form disulfide bridges. These highly stable bonds lock the structure in place: the more numerous they are, the more rigid the fiber. This is, in fact, what distinguishes the keratin of hair and nails, dense in disulfide bridges, from that of the skin, which is more flexible.

The animal kingdom produces two main types of keratin. Beta-keratin, organized into sheets, makes up the feathers, scales, and beaks of birds and reptiles. Alpha-keratin, organized into helices, is found in mammals.

Our hair is therefore made of alpha-keratin, and more precisely of so-called "hard" keratins, which are very high in sulfur. This helical organization explains a familiar property: wet hair can be stretched significantly before breaking, and then return to its initial length.

Natural keratin is found in three main areas:

• hair and body hair, where it forms the cuticle, the cortex, and the medulla;
• nails, which are also made of hard keratin;
• the epidermis, the outermost layer of which is made of keratinized cells that ensure the skin's impermeability.

The human genome contains about fifty keratin genes. Each is expressed in a specific tissue, which illustrates the fine specialization of this protein.

Keratin is not invented at the hair surface: it is built deep inside, in the bulb, at the rhythm of a precise growth cycle and from amino acids that must be supplied daily through diet.

The production of keratin for hair happens beneath the surface of the scalp, in the hair bulb. At its base, the matrix houses keratinocytes that divide at one of the fastest rates in the body.

As they migrate upward, these cells synthesize keratin, become loaded with filaments, and then dehydrate and flatten out. This process is called keratinization. By the end of this journey, the cell is no longer alive: the visible hair shaft is an assembly of keratinized cells.

This precision changes everything. The hair we style no longer has its own biological activity. What we are nourishing is the bulb, and therefore the hair of tomorrow.

Each follicle follows a three-stage cycle:

• the anagen phase, of active growth, lasts from two to seven years and accounts for about 85% of hair at any given moment;
• the catagen phase, of transition, lasts a few weeks;
• the telogen phase, of rest, lasts about three months, at the end of which the hair detaches to make way for a new one.

During the anagen phase, the shaft grows by about one centimeter per month. This figure is essential for setting realistic expectations for any nutritional approach.

The manufacturing of keratin, the hair protein, requires a constant supply of sulfur-containing amino acids. Methionine is an essential amino acid: the body cannot produce it and must obtain it from diet. Cysteine can be produced from methionine.

Several micronutrients are involved in these steps. Vitamin B6 contributes to normal cysteine synthesis, and zinc contributes to normal protein synthesis. Eggs, fish, meat, legumes, and oilseeds provide these amino acids on a daily basis.

Once formed, hair keratin does not renew itself: every technical treatment and every exposure leaves a mark on the fiber, which accumulates over the months.

Coloring and bleaching open the cuticle to allow pigments to penetrate or to oxidize melanin. In doing so, they alter some of the disulfide bonds. Straightening and perms rely on breaking and then reforming these same bonds, which permanently weakens the fiber's architecture.

Heat acts differently. Beyond certain temperatures, particularly those of a hair straightener, hair keratin denatures, like a protein being cooked. Added to this are the frictions from brushing and drying, which gradually lift the cuticle scales.

UV rays oxidize cysteine and degrade disulfide bonds, especially on the surface. The hair then loses strength and color.

Cold, dry winter air increases fiber dehydration. Pollution particles settle on the cuticle and promote its alteration. In other words, even without technical treatments, the hair protein keratin wears out over the months. Summer concentrates these aggressions, which is why it is beneficial to adapt your post-summer hair routine.

An altered fiber is recognizable by several signs:

• dull hair, because lifted scales scatter light instead of reflecting it;
• increased porosity, with hair that absorbs water quickly and dries poorly;
• split ends and more frequent breakage, particularly on fine, brittle hair, whose fiber loses its cohesion more quickly;
• a rough texture that is difficult to detangle.

These signs concern the length that is already formed. They do not indicate a lack of keratin in the body, but rather the wear and tear of a fiber that has sometimes been exposed for several years.

Keratin shampoo or keratin capsules: the name of the active ingredient is the same, but one works on the already formed fiber, while the other works on the hair in formation.

Hydrolyzed keratin is cut into small fragments, peptides, which are integrated into shampoos, masks, and serums. When applied to the fiber, these peptides deposit in the porous areas of the cuticle and coat the hair. The touch becomes smoother and the shine more uniform.

This is the role of keratin restorative care in a cosmetic sense: a surface action on the existing fiber, which fades with subsequent shampoos and therefore needs to be renewed. For hair weakened by technical treatments, it provides an immediate and visible effect on the lengths. Formats, frequency of application, profiles: everything you need to know to choose a keratin hair treatment suitable for your fiber.

Keratin is derived from sheep's wool. A process makes it soluble in the form of peptides, making it suitable for ingestion. It thus differs from raw keratin, which is very difficult to digest, such as that from feathers or hooves.

The difference from cosmetic keratin lies less in the chemistry than in the purpose. One is designed to be applied, the other to be ingested as part of a nutritional intake. The first is aimed at already formed hair, the second at hair currently forming in the bulb.

This is actually the most consistent logic. Cosmetic care handles the existing lengths, while the nutricosmetic approach works over the long term, at the pace of hair growth. The two levels do not replace each other: they complement each other over time.

What can one really expect from a keratin food supplement? The answer comes in two parts: what studies have observed regarding solubilized keratin, and what regulations recognize for the nutrients that accompany it.

The benefits recognized by European regulations are based on specific micronutrients:

• biotin (vitamin B8), zinc, and selenium contribute to the maintenance of normal hair;
• zinc and selenium contribute to the maintenance of normal nails;
• copper contributes to normal hair pigmentation;
• vitamin B6 contributes to the normal synthesis of cysteine.

This is why a well-designed keratin food supplement combines keratin with these nutrients, present at significant doses, i.e., at least 15% of the nutritional reference values per day. The promise is based on them. Biotin is thus at the heart of many biotin food supplements dedicated to hair.

A traditional ingredient in beauty routines, brewer's yeast naturally provides B-group vitamins, proteins, and minerals. It does not have its own specific claim: its value lies in its nutrient content. It fits well into a comprehensive nutritional approach, alongside dietary sources of sulfur amino acids.

The chosen timing, duration, and formula choice determine what a keratin protein-based program will be able to show.

Three moments are particularly suitable for a keratin protein-based program:

• changes of season, especially autumn, a period when seasonal hair renewal intensifies;
• the weeks following coloring, bleaching, or straightening;
• periods when nails split or break more easily, which can be addressed by food supplements for nails.

Hair grows about one centimeter per month. The part formed during the program therefore takes several weeks to emerge, then to gain length. For nails, complete renewal of a fingernail requires several months.

Three months is therefore a reasonable minimum duration to evaluate a keratin for weakened hair program. The one-month format is more of a periodic maintenance.

A few criteria can help distinguish a high-quality formula:

• the form of keratin, here a water-soluble keratin documented by published studies, with a dosage aligned with the one studied;
• the presence of nutrients with an authorized claim, at a significant dose;
• transparency regarding the origin of ingredients;
• a dosage form adapted for daily intake over several months.

As a pioneering nutricosmetics laboratory in France, Biocyte has built its formulas on these principles: documented active ingredients, justified dosages, and combinations with the micronutrients of the hair fiber.

• Beer C, Wood S, Veghte RH. A clinical trial to investigate the effect of Cynatine HNS on hair and nail parameters. The Scientific World Journal, 2014;2014:641723. doi:10.1155/2014/641723
• Wang B, Yang W, McKittrick J, Meyers MA. Keratin: structure, mechanical properties, occurrence in biological organisms, and efforts at bioinspiration. Progress in Materials Science, 2016;76:229-318.
• Moll R, Divo M, Langbein L. The human keratins: biology and pathology. Histochemistry and Cell Biology, 2008;129(6):705-733.
• 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 edition, Springer, 2012.
• Almohanna HM et al. The role of vitamins and minerals in hair loss: a review. Dermatology and Therapy, 2019;9(1):51-70.
• Commission Regulation (EU) No 432/2012 of 16 May 2012 establishing a list of permitted health claims made on foods.