Each strand of hair has a root and a shaft. The root and a small section of the shaft lie in the follicle, just below the surface of the scalp. At the bottom of each follicle, is a projection called the papilla, which contains the artery that nourishes the root. The papilla manufactures the keratin, or protein. As new cells form around it, the old cells fall away and die. These dead cells are gradually pushed up out of the follicle and become part of the hair shaft.

Hair grows at a rate of about 1-1.5cm per month, faster in summer than in winter and more at night than in the daytime. Hair is lubricated by the sebaceous glands or oil glands. The anagen phase is when a new hair is produced and lasts for about 4 years. At the catagen phase, the production of cells slows down considerably before stopping completely; this lasts for about 3-4 weeks.

Next comes the telogen phase when the hair follicle retracts and its base moves up towards the surface of the scalp. A new hair now grows regularly and expels the old one. Every hair follicle has an average of 25 cycles in its 4-year lifespan. If we constantly lose hair every few months on the same place, once the 25 cycles are up, no more hair will grow in that particular spot again.