A class of drugs already approved by the U.S. Food and Drug Administration for treating rheumatoid arthritis is raising hairs in the research community—literally. Previous studies had shown that Janus kinase inhibitors, including tofacitinib and ruxolitinib, can treat alopecia areata, an autoimmune disease that causes bald patches when immune cells attack hair follicles. The researchers noticed that, when applied topically, the treatment seemed to be directly spurring robust hair growth. New research suggests that the drugs can do the same even in mice without the autoimmune disease. When researchers applied the drugs topically to the right side of mice whose hair follicles were in a resting phase, the difference was clear: 90% of the treated mice had hair growth within 10 days. And after 3 weeks, untreated mice in a control group (left) remained bald, while those given tofacitinib or ruxolitinib (right) had hair-covered right sides. The drugs, it turned out, had kick-started their hair cycles, putting follicles into an active growth phase. Results were similar when the scientists grafted healthy human scalp skin onto mice, and further experiments showed that the new hair growth was normal at a molecular level, the team reported online today in Science Advances. But it might be some time before you can use the drugs to treat your own bald patches: Scientists still have some ways to go before knowing whether the drugs work on male or female pattern baldness.