The team cut out a square centimetre of skin from the backs of mice two weeks after their hair follicles had formed. After 14 to 19 days the wounds had closed and formed new. When the researchers added Wnt proteins - signalling molecules usually involved in embryonic development - the number of follicles doubled and the skin healed with less scarring. This suggests that wound healing may trigger an embryonic state in skin, says Cotsarelis. Surprisingly, the new follicles originate from stem cells that are not usually involved in creating hair follicles.