Hundreds of thousands of people with alopecia areata may one day benefit from a drug that can cure baldness in months.
A study of the twice-a-day pill found four in 10 patients with the condition were able to regrow nearly a full head of hair within half a year.
The main scientist behind the drug does not expect it to work for the millions of men who lose their hair as they age, however.
Alopecia is the general medical term for hair loss. Alopecia areata — one type of hair loss — is caused by the body attacking its own healthy hair follicles.
Made by the US drugs company Concert Pharmaceuticals, the new therapy works by dampening the immune response, preventing it from going haywire.
There are currently no cures for alopecia areata — although other drug firms are also trialling drugs to help reverse the hair loss. Steroids and other medications can help kick-start hair growth, however.
Around 100,000 people in the UK and 6.8million in the US have the condition. It can rob people of their hair in a few weeks.
Because of the speed of hair loss, the disease can cause low self-esteem, depression and anxiety.
Famous sufferers include actress Jada Pinkett Smith. Her husband Will Smith landed in controversy at this year’s Oscars in March, after he slapped comedian Chris Rock for joking about his wife’s baldness.