Hair growth phases is the term used to describe a three-stage cycle that each individual body hair goes through during its growth.
What are the hair growth phases?
Hair growth phases is the term used to describe a three-stage cycle that each individual body hair goes through during its growth. The cycle of hair growth phases consists of a growth phase, a phase of transition, and a phase of stagnation and loss of hair. The growth phase is by far the longest of the three phases and lasts approximately between 2 and 6 years. The duration depends on the age and the place of hair growth on the body. The growth of hair is regulated by the so-called hair follicles, which are located under the skin. At the lower end of the hair follicles new hair roots are formed again and again by cell division, from which new hair can grow again. Due to the constant repetition of these cell renewals, the hair grows by 0.3 to 0.5 mm every day. About 85 percent of body hair is in this phase. After completion of the growth phase, the hair enters the transition phase. In this phase, the hair root is separated from the hair over a period of 3 to 4 weeks and the hair is slowly pushed towards the surface of the skin. At the beginning of the last phase, the hair is completely detached from the root and is therefore no longer supplied with nutrients. The hair follicle becomes active again and starts forming a new hair, which slowly displaces the old one until it finally falls out. Approximately 15 percent of body hair is in this process at any given time, which lasts just under 3 to 5 months.
Function and task
The hair growth stages perform a variety of important tasks and functions for humans. By far the most important function of the cyclic growth of hair is the elimination of diseased or damaged hair. If hair were to start growing only once and grow through to the end of life, there would be no chance to replace damaged or dead hair. Dead hair would then fall out without growing back and early baldness would be the likely result. Damaged hair would also remain on the body without being able to serve its proper purpose. Sun rays and with them dangerous UV and infrared rays could then hit the scalp against little or hardly any resistance and damage it, the head would no longer be properly protected from cold or heat. However, because the hair is constantly dying and being renewed, healthy and strong hair can always grow back and guarantee full protection. Hair growth plays another important role in the transition from adolescence to adulthood. In this phase, the fine, colorless vellus hair, which covers the entire body with few exceptions, forms in some places into the strong, pigmented terminal hair. Thus, in men, the hair on the beard, in the pubic area, on the armpits as well as on the chest, back and shoulders becomes terminal hair, in women especially in the pubic area and on the armpits. In addition, hair growth phases also limit the length of eyelashes, eyebrows, and nose and ear hair, which, if left unregulated, would grow longer and longer, severely impairing vision, hearing, and smell.
Diseases and ailments
The natural hair growth phases can be affected or even completely stopped by a number of diseases and ailments. By far the most common of these ailments is alopecia, which is hair loss in which the hair that falls out is not renewed. This can occur in various forms. Androgenetic hair loss is genetically determined and is triggered by an increased sensitivity of the hair follicles to dihydrotestosterone, a steroid hormone. As a result, the hair follicles atrophy more and more and the growth times of the hair become shorter and shorter. In alopecia areata, on the other hand, the hair falls out in circles in various parts of the body. This is caused by a reaction of the immune system, which regards the hair cells as foreign bodies and therefore destroys them with the help of an inflammatory reaction. However, since the follicles remain intact, the bald patches usually grow back. As a result of iron deficiency, infections, hormonal fluctuations, thyroid disorders and stress, diffuse hair loss can also occur, in which hair falls out from the entire head.In hypertrichosis, many and dense hairs grow even in areas that otherwise have little or no hair. It can be limited to individual areas or affect the entire body. It can be inherited, but can also be newly formed. Hair growth phases are thus subject to a constant process that can be interrupted or stimulated by many factors.
