Wound at different stages of healing (A-C). The blue lines represent "clones" of cells originating from hair follicle stem cells. As the wound heals, the hair-follicle-derived cells migrate linearly toward the center of the wound in an apparent effort to heal the wound as quickly as possible. A, two days after wound. B, five days after wound; blue streaks indicate that clones move inward. C, eights days after wound, the epidermis has completely closed.

Photo Credit: George Cotsarelis, MD, University of Pennsylvania School of Medicine; Nature Medicine