Hair Physiology

The Hair Cycle

Hair grows in groups of 1 to 4 hairs called hair follicles. We are born with all the hair follicles we will ever have in the scalp (approximately 100,000). Hair follicles replenish themselves by going through three phases, the Anagen phase; Catagen phase; and Telogen phase, known as the hair cycle.

This is the reason why hair grows to a particular length and thickness. The duration of the Anagen phase, between 2 to 6 years, determines the length of the hair and the hair bulb determines the hair shaft diameter. The growth rate is approximately 1cm per month.


Hair is much more complicated than it appears. It helps transmit sensory information and creates gender identity. Hair is important to the appearance of men and women. There is hair on all the major visible surfaces of the body but the hair on the head is the most likely to be lost.

Structure of the hair

Before considering the scalp as a whole, it is relevant to consider the structure of the hair follicle. Hair follicles are the prize in hair transplant surgery the skilful harvesting and replanting of them is the essence of high quality hair transplantation.

The hair follicle

For the above reason, in modern hair transplant surgery for male pattern baldness, great emphasis is placed on the follicular unit as a discrete entity.