Alopecia areata is a common autoimmune disease that causes sudden hair loss on the scalp, face, and sometimes other areas of the body.

There are different degrees of severity of alopecia areata. The three main types of alopecia areata are patchy alopecia totalis (complete hair loss on the scalp) and alopecia universalis (complete hair loss on the body).

Androgenetic alopecia is a common form of hair loss in men and women.

In men, it is also referred to as male pattern baldness, and in women, it is referred to as female pattern baldness. In men, hair falls out in a clearly defined pattern, starting above both temples.

Lichen planopilaris (LPP) is a rare cutaneous variant of lichen planus (see there) with changes in the hair follicles.

It can occur in this form in isolation or in association with more common forms of lichen planus, usually the classic type and/or oral lichen planus.

Central centrifugal scarring alopecia (CCCA) is a form of scarring alopecia on the scalp that results in permanent hair loss. It is the most common form of scarring alopecia in black women.

However, it can be seen in men and in people of all races and hair colors (although rarely). Middle-aged women are most commonly affected.

Traction alopecia can be reversed if you stop pulling your hair back, but if you don't intervene early enough, hair loss can be permanent.
Doctors in Greenland first recognized the condition in the early 20th century. They discovered that women who wore tight ponytails lost hair at the hairline.

Telogen effluvium is the excessive loss of hair in the resting or telogen hair state following metabolic stress, hormonal changes or medication intake.

Due to the shape of the root, telogen hair is also called club hair. The scalp of a normal, healthy person consists of about 85% anagen hair and 15% telogen hair.