The US Food and Drug Administration has approved Pfizer Inc's drug to treat hair loss caused by an autoimmune disease, the company said on Friday.

The drug, branded as Litfulo, has been approved for people aged 12 years and older suffering from severe alopecia areata (AA), a condition where the immune system attacks hair follicles and causes hair to fall out, often in clumps.

The FDA's decision makes Litfulo the first to be allowed for the treatment of the condition in adolescents.