The hair is made up of a protein called keratin which is also the main constituent of nails. A specialized structure of the skin called ‘Papilla' produces the hair as shown in the figure. The papilla is surrounded by a sac-like structure called the ‘Hair follicle' which also surrounds rest of the hair root within the skin. The part of the hair outside the skin surface is called a shaft.
Alopecia Areata is considered to be an auto-immune condition in which the immune system of the body (which protects the body from bacteria and viruses) mistakenly attacks the hair follicles and destroys them. This leads to hair loss in the affected area.
The commonest presentation of Alopecia Areata is the appearance of bald patches on the scalp. In most cases, hair falls out in small, round patches about the size of a small coin. The patient may have single or multiple such patches. In some cases, these patches may remain static, whereas in some cases the patches may spread to involve larger areas of the scalp. In some cases, hair loss is more extensive. Although it is not very common, the disease can progress to cause total loss of hair on the head (Alopecia Areata totalis) or complete loss of hair on the head, face, and rest of the body (Alopecia Areata Universalis).