The first cold week tends to show up on your legs before anywhere else. You take off black tights or dark jeans and there is a fine white dust on the inside of the fabric. A fingernail catches your shin by accident and leaves a pale line that stays. Your face feels fine, and so do your forearms. Only the shins have gone white. The usual response is to go after the flakes. A sugar scrub on Sunday, a rough mitt in the shower, a body wash with "exfoliating" on the label. For one evening your...