Alopecia areata can be diagnosed by a physician. In addition to taking a medical history and performing a physical examination, inspecting the scalp and pattern of hair loss is often sufficient to diagnose alopecia areata or a similar disorder (e.g., male pattern baldness, androgenetic alopecia). Hairs may also be tugged or pulled out to determine hair strength.

If a diagnosis is not clear, a physician may take a sample of hair and scalp for laboratory analysis (biopsy). In some cases, blood tests may be used to test for other medical conditions that cause hair loss (e.g., overproduction of thyroid hormone [hyperthyroidism]).