Hair consists of the shaft, which grows and rises above the skin surface, and the root, which is located in the small fossa within the derma thickness and is anchored into a special follicle (hair follicle).
Hair is composed of a corneal protein substance (keratin), rich in sulfur and nitrogen. After several growth stages, old hairs are shedded and are replaced by the new ones. Long hairs, growing on the human scalp, live for 4-5years. The substance, produced by the sebaceous glands, located next to each other in the hair follicle has a protective effect for hairs. Hair color is conditioned by the melanin pigment content. Pigment quantity decreases with age, and its distribution becomes disrupted. There are also pigment-free hairs, for example in case of the albinism.
Normally people lose 60-100 hairs per day. The disturbance of the hair growth and replacement functions can lead to the baldness or excessive hair growth (hairiness).
The hair follicle is a cyclically developing structure which passes through the following phases:
1.Anagen, which is divided into the early anagen and mature anagen subphases. This is the active growth phase.
2. Catagen, during which the hair papilla atrophy is observed, leading to the feeding disorder of the actively developing bulb cells. Cells stop to develop and their cornification occurs. This is the transitional phase.
3. Telogen, which is the resting phase.
It’s thought that the hair growth cycle starts with the catagen phase which lasts for several weeks. It’s followed by the telogen phase (lasts for several months) which gradually turns into the early anagen phase. The anagen phase lasts for 4-5 years. This phase becomes shorter with age. Normally 80-90% of hairs are in the anagen phase, 1-2% are in the catagen and 10-15% are in the telogen phase. Hair loss is observed for account of the hairs, which are in the telogen phase.