More than 80 percent of men and nearly half of women experience significant hair loss during their lifetime. For many, the thinning begins well before middle age. Everyone has a story to share about the annoying effects of hair loss, which range from daily inconveniences to emotional distress. Few effective treatments exist, and they often come with side effects.

Harvard stem cell biologist Ya-Chieh Hsu and her team have identified two biological pathways that regulate hair loss and, correspondingly, two potential ways to grow them back. Hair follicle regeneration is largely governed by a special cell type called hair follicle stem cells, which respond to both hormonal and neuronal signals. Dr. Hsu’s lab showed that the stress hormone cortisol inhibits hair follicle regeneration by suppressing a gene called Gas6. Correspondingly, “adding Gas6 was sufficient to activate hair follicle stem cells that were in the resting phase and to promote hair growth”, said Sekyu Choi, lead author of the study, in an interview with The Harvard Gazette. In another study, Dr. Hsu’s lab discovered that the same nerves generating goosebumps also activate hair growth. Topical application of the asthma medication isoproterenol mimicked such neuronal stimulation and potently increased hair growth. These results pave the way for developing next-generation cosmetology products with proven effectiveness against hair loss.