The human hair follicle is an intriguing structure. The hair follicle can be divided into 3 regions: the lower segment (bulb and suprabulb), the middle segment (isthmus), and the upper segment (infundibulum). The lower segment extends from the base of the follicle to the insertion of the erector pili muscle (also known as the arrector pili muscle). The middle segment is a short section that extends from the insertion of the erector pili muscle to the entrance of the sebaceous gland duct. The upper segment extends from the entrance of the sebaceous gland duct to the follicular orifice.

The process of hair growth occurs in three distinct phases:

Anagen Phase

Anagen Phase is the active growth phase of hair follicles during which the root of the hair is dividing rapidly, adding to the hair shaft. During this phase the hair grows about 1 cm every 28 days. Scalp hair stays in this active phase of growth for 2–7 years; this period is genetically determined. At the end of the anagen phase an unknown signal causes the follicle to go into the catagen phase.

Catagen Phase

Catagen phase is a short transition stage that occurs at the end of the anagen phase. It signals the end of the active growth of a hair. This phase lasts for about 2–3 weeks while the hair converts to a club hair. A club hair is formed during the catagen phase when the part of the hair follicle in contact with the lower portion of the hair becomes attached to the hair shaft. This process cuts the hair off from its blood supply and from the cells that produce new hair. When a club hair is completely formed, about a 2-week process, the hair follicle enters the telogen phase.

Telogen Phase

Telogen phase is the resting phase of the hair follicle. The club hair is the final product of a hair follicle in the telogen stage, and is a dead, fully keratinized hair. 50 to 100 club hairs are shed daily from a normal scalp.
When the body is subjected to extreme stress, as much as 70 percent of hair can prematurely enter the telogen phase and begin to fall, causing a noticeable loss of hair. This condition is called telogen effluvium.

Hair loss (alopecia) is a disorder in which the hair falls out from skin areas where it is usually present, such as the scalp and body. This loss interferes with the many useful biologic functions of the hair, including sun protection (mainly to the scalp) and dispersion of sweat gland products. Because hair has psychological importance in our society, patients with hair loss suffer tremendously.

Androgenetic Alopecia

Also known as male pattern baldness or female pattern baldness. It is a thinning of the hair to an almost transparent state, in both men or women. It is thought to be a hereditary form of hair loss and is the most common type of progressive hair loss.

Telogen Effluvium

In general, telogen effluvium is self-limited, and no treatment is necessary after the initial cause is removed. Identifying the trigger is helpful to avoid relapses and new shedding periods. Common triggers for telogen effluvium are medications, illness, childbirth, and crash diets. The etiology of telogen effluvium is generally elucidated by history, with special concentration on events that have preceded the shed by 6 weeks to 4 months.Chronic or persistent telogen shed heralds androgen alopecia or other metabolic or disease states, such as thyroid disorders. If telogen shedding persists, a more intense medical evaluation is needed.

Alopecia Areata

Alopecia areata is understood to be an autoimmune condition which causes patchy hair loss. It can result in a single bald patch or extensive patchy hair loss.

Scarring Alopecia

Scarring Alopecias refers to a rare group of disorders that destroy hair follicles. Occasionally they are referred to as cicatricial alopecias. The hair follicles are replaced with scar tissue (hence the name). In some cases the hair loss is without symptoms and can go unnoticed for long periods. In other cases the hair loss is accompanied by burning, itching and pain and is more progressive. It occurs in men and women of all ages but it less common in children. Frontal Fibrosing Alopecia and Lichen Planopilaris are two of the well known Scarring Alopecias.

Premature greying

Premature greying of hair can have negative effects on appearance, confidence, self-esteem, and social acceptance of the affected individual. Hair is said to have greyed prematurely if it occurs before the age of 20 years in Whites, before 25 years in Asians, and before 30 years in Africans.