Civilization taxes skin’s capacities. On a given weekend we might dig in the garden gloveless, spill kerosene on our hands at the barbecue grill, and clean paint brushes with turpentine, then scour it all off with abrasive powder and a roughened pad. Somehow skin survives. If I clean out a muddy gutter with my bare hand or reach in to unstop a toilet, I’ll encounter a swarm of bacteria, yet my skin cells loyally guard against their entering my body. Each of us carries as many bacteria on our skin