One should know about the hair cycle in order to understand the hair loss. Hair follicle is an anatomic structure that forms the hair and allows it to grow. The hair comprises of a sort of protein named keratin. In human beings, hair has a cycle that continuously enters into growing and falling phases, and there are 3 phases in this cycle: The anagen phase is the growing phase of the hair; the telogen phase is the resting phase of the hair; the catagen phase is the degradation phase of the hair.
The anagen phase lasts approximately 2-8 years and ends with the catagen phase where the hair degrades for 2-4 weeks. The telogen phase starts after this and then it lasts 2-4 weeks. Hair degradation only begins with the start of the next anagen phase and takes place with the new hair growth. It is natural that one experiences a hair loss of 50-100 on a daily basis in the telogen phase and this is an expected result of hair cycle. These hairs grow again. Approximately 10% of the whole hair on our head are in the telogen phase.
Drug use, radiation, chemotherapy, chemical exposure, hormonal and nutritional factors, thyroid diseases, general or local skin diseases, and factors like stress may affect the hair growth cycle, and cause permanent or temporary hair losses (alopecia). Androgens (testosterone and dihydrotestosterone) are the factors that have the most effect on hair growth. Androgen hormones have an important role in the generation of the arm pit hair, pubic hair and facial hair in the adolescence period. What’s interesting is that the growth of hair in the scalp is independent of the androgen hormones but these hormones are responsible of women or male type alopecia.