Scientists from the Columbia University Medical Centre in New York were able to identify exactly which cells were destroying the hair follicles –they are called T-cell immune cells.
They then tested several treatments known to stop the action of these cells on mice and all resulted in them growing back hair.
The researchers then tested one of these drugs – ruxolitinib – on three men with the condition who were almost completely bald.
They were given a pill to take twice a day and between four and five months all had regrown a full head of hair

Ruxolitinib (INC424, INCB18424, trade names Jakafi and Jakavi, by Incyte Pharmaceuticals and Novartis) is a drug for the treatment of intermediate or high-risk myelofibrosis, a type of bone marrow cancer.[2][3] It is also being investigated for the treatment of other types of cancer (such as lymphomas and pancreatic cancer),[4] for polycythemia vera,[4] for plaque psoriasis, and for alopecia areata [5].