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 shed and are replaced by new ones. The substance produced by the sebaceous glands and keratin are located beside each other in the hair follicle providing a protective effect on the hairs.
Hair color is determined by the melanin pigment content. With age, pigment quality decreases and its distribution becomes disrupted. Hairs can be absent of pigment, resulting in albinism.
Normally, people lose 60-100 hairs per day. A disturbance in hair growth and replacement process can lead to baldness or excessive hair growth.
The hair follicle is a developing structure which cycles through the following phases:
1.Anagen – This is the active growth phase. It is divided into sub-phases, early anagen and mature anagen phases.
2.Catagen – This is the transitional phase. During this phase, hair papilla atrophy is observed which leads to the feeding disorder of the actively developing bulb cells. The cells stop development and cornification occurs.
3.Telogen – The resting phase.
It is thought that the hair growth cycle starts with the catagen phase which lasts for several weeks. It is then followed by the telogen phase (lasting several months), and gradually turns into early anagen phase. The anagen phase lasts 4-5 years, and becomes shorter with age. Normally, 80-90% of hairs are in the anagen phase, 1-2% are in the catagen phase, and 10-15% are in the telogen phase. Hair loss is observed and taken in account of hairs that in the telogen phase.