The disease can vary in severity, but for some, it can be life-altering — a total loss of body hair, including eyelashes and eyebrows, even nose hair and hair in the ears. And, until recently, for those with alopecia areata, there was no treatment to make the hair grow back.

But on Monday, the Food and Drug Administration approved baricitinib, a drug made by Eli Lilly that regrows hair by blocking the immune system from attacking hair follicles. Two other companies, Pfizer and Concert Pharmaceuticals, are close behind with similar drugs, known as JAK inhibitors. The drugs are already on the market for the treatment of rheumatoid arthritis and other autoimmune diseases. F.D.A. approval is important for insurance coverage of these expensive drugs, which have a list price of nearly $2,500 a month.

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The Lilly drug was studied in two trials, sponsored by the company and published last month in the New England Journal of Medicine, involving 1,200 patients with severe alopecia areata. Nearly 40 percent who took the drug had complete or near-complete hair regrowth after 36 weeks. After a year, nearly half of the patients had their hair back.

Read more: NY Times