Adult men have about 130,000 scalp hairs and women about 150,000. Every day about 50 hairs die and, in ideal conditions, are substituted by new ones, since the follicles have synchronized growth cycles at any one time. When psychological stress, metabolic problems, hormone disease or deficiencies in specific micronutrients intervene to upset the equilibrium of follicle life conditions and hair growth the follicles in the anagen phase might pass directly to the telogen phase, causing an early hair loss.

If the stressing stimulus or the pathological condition remain, the hair can modify its diameter and its length.