What is Keratin?
This is an important protein compound that skin, hooves, horns, claws, fur, skin, hair, and nails are all made out of. Aside from forming a multitude of our physical features, keratin also plays a wide variety of roles within the body such as regenerative healing, cell growth, cell signaling, and apoptosis (cell death). Originally, all keratin was thought to be the same type of protein, but scientists have since discovered there are actually 54 different genetic expressions for humans alone.
Different Types of Keratin
Although there are many different forms, each keratin falls into two basic types:
- 1a – this first type is what forms the toughened exterior portion of the body such as the hair and nails. These proteins are called “trichocytic”, meaning that these proteins are much “harder” than the second type. These structures largely have no feeling except for where the nerves extend beneath the skin. These proteins are very high in sulfur.
- 2a – this second type includes all “soft” keratins. This group includes cytokeratins, which are keratins still within the body that combine with epithelial cells to get special functions accomplished. Epithelial cells simply refer to any cell that makes up the lining of a cavity such as the lungs or a hair follicle. They can be assigned special tasks such as wound closure, cell division, apoptosis and more. Epidermal (skin) keratins fall under this category because the epidermis is much softer than hooves, claws, nails, etc.
According to a 2008 study, nearly half of all of keratins reside in the hair follicles. These proteins play a crucial role during the formation and maturation of the hair itself during all three stages of growth.
- Anagen – during this initial phase, keratins help direct the mitotic activity (cell division rate) of epithelial cells. A specific keratin in particular, called K17, is responsible for “the persistence of the anagen (growth) state in hair follicles”, according to a 2006 overview.
- Catagen – during this second phase, the hair follicle begins to shrink. Keratin is responsible for the controlled apoptosis (cell death) that causes structures in the hair follicle to be destroyed so that the follicle may shrink in preparation for the next phase. As the hair matures, it also begins to undergo keratinization, a process in which keratin infuses with the hair to provide durability and structural support. These specialized proteins, in essence, help anchor the hair to the scalp.
- Telogen – for this final phase, the hair is fully composed of keratin, and is now ready to make an exit off of the scalp. Just like nails and the outer layer of the skin, the hair has become completely hardened and is no longer “living”.
The epidermis (the outermost layer of the skin) is made of deadened keratinocytes, which are epithelial cells that have been assigned a specialized task. These specialized cells travel upwards from the lower levels of the skin until they form the epidermis.