Alopecia areata (AA) is a common, usually patchy, nonscarring hair loss condition affecting any hair-bearing surface. The lifetime risk in the United States has been estimated at 1.7% [1,2]. AA equally affects men and women. It is the most common hair loss complaint in children; approximately 20% of patients with AA are children and as many as 60% present with their first patch before the age of 20 [3,4] (Figure 5.1). Colombe et al. suggest a bimodal pattern for AA, with an early-onset form associated with greater severity, long duration, and family history of the disease and a late-onset form characterized by milder severity, shorter duration, and low family incidence [5] (Figure 5.2). Alopecia universalis after 1 year in a 3-year-old girl. (a) Front view showing loss of hair on scalp, eyebrows, and eyelashes; (b) side view; (c) back view. This early onset form of alopecia areata (AA) is associated with greater severity, longer duration, and greater probability of a positive family history of AA. Human leukocyte antigens studies suggest this early onset group of severe AA patients is a genetically distinct group. They are prognostically and therapeutically distinguishable, too. https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9780429160592/7292645f-1b32-4bc4-913a-05f7ff2e9681/content/fig5_1.jpg"/> (a) Simultaneous circumscript alopecia in mother and son; (b) simultaneous ophiasis in mother and daughter. https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9780429160592/7292645f-1b32-4bc4-913a-05f7ff2e9681/content/fig5_2.jpg"/>