In order to elucidate the reasons and treatment modalities of hair loss, hair constitution, and hair quality should be defined.
Hair on human body has a role of sustaining body temperature, protecting the body against external factors, contributing sensation, and complementing aesthetic appearance of the body. Except in the palm, sole, and glans penis, hair can be found in all surfaces of human body in varying thickness and color.
Terminal hairs are the thickest. Hair, beard, and chest hair are of this kind.
Hair is produced and grows in a layer called 'hair follicle', which surrounds the hair and also called 'hair root'. Unlike common belief, hair does not constantly grow. The growth ceases at one point and then falls out. In the place of hair lost, a fresh hair is produced through hair follicle. This process, which is referred to as 'the life-cycle of hair', successively continues in 3 stages .
1. Anagen (growth) stage: this stage involves continuous growth of the hair produced. It lasts as long as 3 years.
2. Katagen (passage) stage: the growth activity gradually ends. It lasts 1-2 weeks.
3. Telogen (inactive and fall-out) stage: hair remains at the same length without any growth. It lasts about 3-4 months. At the end of this period, the hair falls out of its root either by the freshly produced hair pushing the old one out, or a hairbrush pulling it out. With the arrival of a fresh hair, the cycle continues.
Head scalp contains approximately 100.000 hairs, 85-90 % of which are in anagen stage and 10-15% of which are in katagen and telogen stages. An average of 100-150 hair fall-outs a day is considered a normal physiological process. Contrary to common belief, frequent shaving does not increase the hair growth or density. In anagen stage, the mean hair growth is 0.37 mm. At the end of growth stage, hair may grow as much as 25-100 cm ( in men, down to the back; in women, down to waistline)
In hair loss, the duration of the stages mentioned is shorter.