Definition

Alopecia is the partial or complete loss of hair—especially on the scalp—either in patches (alopecia areata), on the entire head (alopecia totalis), or over the entire body (alopecia universalis).

Description

A basic understanding of hair biology and normal hair development is essential in distinguishing normal versus abnormal hair loss in children and adolescents.

Hair consists of the shaft and the root, which is anchored into a follicle beneath the epidermis. Hair is formed by rapid divisions of cells at the base of the follicle. Except for a few growing cells at the base of the root, hair, which is composed of keratin and other proteins, is dead tissue.

An individual hair follicle has a long growth phase, producing steadily growing hair for two to six...