Alopecia areata is hair loss caused when the immune system attacks hair follicles, where hair growth begins. Contact immunotherapy may be the most effective treatment for severe alopecia areata.footnote 1 A common medicine used is diphenylcyclopropenone (DPCP).
DPCP, a liquid, is “painted” on the scalp once a week. The concentration of the solution is increased at each treatment session until a mild allergic reaction occurs. Hair growth may appear within 3 months of beginning treatment.