Keratins: Function & Diseases

Keratins are special substances. They are found in human and also in animal organisms. The name “keratin” comes from the Greek and means “horn”. Therefore, the amino acids important for the body are also called horn cells.

What are keratins?

The umbrella term “keratins” covers various hydrophobic fibrous proteins that are the main component of hair, finger and toenails, and the upper layer of the skin (epidermis). It refers to both the fibrous proteins themselves and the microfibrils they form. In animals, the important keratin cells (keratinocytes) are additionally found in horns, hooves, claws, feathers, spines, carapace and beak. The natural protein is produced by the body itself and is normally always present in sufficient quantities. Medicine distinguishes between alpha and beta keratins. Alpha keratins are found exclusively in mammalian cells. Hair keratins have a lower strength than those of finger and toenails. The horn substance is colorless by nature and only receives its respective color tint through the pigment melanin. Thanks to the thread-like structure of the horn cells and their special elasticity, the hair can be treated with perms.

Function, effect and tasks

The keratin cells surround the medullary cells of the hair nucleus with a tight elastic layer of tiny scales. They smooth the surface of the hair, providing natural shine. This allows the hair to be pulled and twisted without tearing. The keratinocytes have a cell wall stabilizing effect and thus provide optimal cell protection. They also increase the strength and resistance of the nails. Without the stabilizing effect of keratin, scratching or holding on with the nails would not be possible at all. In the case of facial skin, it also strengthens the cells so that the epidermis becomes elastic. The wound-healing effect of keratinocytes is exploited in outpatient transplantation. It removes a few keratin cells from the hair of patients with open wounds and multiplies them in a nutrient solution. A few weeks later, the wound is then covered with the newly formed skin tissue. Another four to six weeks later, the wound has then closed. Dirt and pathogens can no longer penetrate and lead to infections. The new skin has the same properties as the skin that was previously on the affected area. Keratin cells are also used to diagnose tumors in the human body: if a cancer cell contains keratin, the physician can conclude that the cancer was formed by epithelial cells. Further information about the type of cancer is provided by immunological detection of keratin subtypes.

Formation, occurrence, properties, and optimal values

The water-insoluble horn cells are proteins found in epithelial cells as loosely organized keratin filaments before keratinization (keratin precursor). The keratin found in hair is less solid than that found in nails. The reason for this is that the one protein building block contained in keratin, L-cysteine, forms a smaller number of disulfide bridges (sulfur compounds) there with other amino acids than in the nail cells. The amino acid cysteine is responsible for the high sulfur content in keratin. This is why burnt hair, for example, also smells strongly of sulfur. Keratin cells have such a solid structure that they cannot be destroyed by bacteria and other microbes. They are very pliable, but cannot break under normal circumstances. In addition, keratinocytes are markedly insensitive to temperature. Neither extremely cold nor extremely warm temperatures can change their properties. Keratin forms two subfamilies: type A comprises proteins that react acidically, while type B is neutral-based. The ability of cysteine to form sulfur bridges is used by modern cosmetics in the perm treatment of hair: In this procedure, the cross-links are first separated and then re-established.

Diseases and disorders

Keratin is normally a fairly resistant substance. However, the protective layer of the hair can become permeable due to salt water (swimming vacations) and excessive exposure to the sun: The hair becomes dull and can even break under heavy stress. Frequent hair drying with a too hot hairdryer and shampoos with a high content of surfactants can also damage the dandruff layer.The result is dry dull hair and split ends. To regenerate hair affected in this way, the patient should supply it with keratin in the form of a highly concentrated hair serum containing cysteine. It immediately penetrates the cuticle layer and closes it. Keratin care shampoos, with which he can wash his hair, also have a restorative effect. After washing out the shampoo, the regenerating effect of keratin is reflected in the fact that the hair is easier to comb than before. Additionally added keratin provides the so-called anti-frizz effect: the hair lies smoothly against the scalp. Damaged skin can be healed with special keratin-containing body lotions and creams. To prevent a keratin deficiency, a protein-rich diet is recommended, whereby the emphasis should definitely be on vegetable proteins. The doctor recognizes that a patient has a keratin deficiency by his strongly curved nails, nail grooves and disturbed hair growth. The cause is a liver disease. The damaged organ is no longer able to produce sufficient quantities of the keratin-forming amino acids cysteine and methionine.