Alopecia areata (AA)

Alopecia areata affects the hair follicles. Research describes the condition as resulting from a loss of the hair follicle's normal immune privilege, allowing T cells to mistakenly target the follicle and interrupt the hair growth cycle. Because the follicle itself is usually not destroyed, hair can regrow once the inflammatory attack quiets, which distinguishes alopecia areata from scarring forms of hair loss. Genetic susceptibility combines with environmental triggers to bring on episodes, and the condition often runs in families or alongside other autoimmune conditions, most commonly autoimmune thyroid disease.

Reviews describe a lifetime prevalence of roughly 2 percent of the general population worldwide, though estimates vary by region and are notably higher in North African, Middle Eastern, and North American populations than in parts of Asia and Western Europe.

Common signs

Sudden patchy hair loss, classically in round or coin-shaped bald spots on the scalp, though it can affect the beard, eyebrows, eyelashes, and body hair. Some people lose all scalp hair (alopecia totalis) or all body hair (alopecia universalis). The bald skin is usually smooth, without scarring, and many also notice pitted or ridged fingernails and toenails.

This is a plain-language summary for orientation, not a diagnosis. Mechanisms are described as current understanding, not settled fact. Work with your own clinician for your care.