SCIENTISTS FOUND TESTOSTERONE IS WHY MENS SKIN HEAL SLOWER

A team at ULB and Cambridge spent five months filming skin stem cells inside living mice, which is an absurdly long time to stare at a rodent's ear. What they saw: in females, when a stem cell divides, the two daughter cells stay in step and tend to divide or mature at the same moment. In males, every cell freelances on its own schedule. Female mice also closed a small wound faster than males did, and the team put that down to the skin cells themselves responding sooner and working together. Then they went looking for the guilty hormone. They castrated the male mice, and male skin started behaving more like female skin. They gave them DHT, an active form of testosterone, and the male pattern came right back. In females, the mirror experiment pointed at estrogen, which drives stem cell proliferation and helps coordinate it. First author Dan Engelman said the team was "surprised to discover strong differences in the way stem cells renew the skin in females and males." Before you write this off as mouse business, they also put testosterone on human skin rebuilt in the lab, and it sped up stem cell differentiation there too. The wound-healing half is still mice only. The team also couldn't rule out immune cells and the skin's scaffold chipping in. The paper is in Nature, and Blanpain says skin cancer is the next question.

Why you should give a shit: Female mice closed their wounds faster, and the hormone men pay a clinic to top up is the same one that knocks the repair crew out of sync, which is worth knowing before medicine keeps assuming skin is skin.