It used to be so simple. You were a kid. You fell down, and skinned your knee. You cried. Mom came to the rescue, washed off your wound and applied hydrogen peroxide or mercurochrome. You cried again.

The customary instruction for bandages after you get a wound, whether from a doctor or a boo-boo, is to keep it clean, keep a bandage on it, which you should usually change every day in order to keep ...