Please, we beg of you, just quit. On top of a long list of evils, smoking breaks down elastic fibers in the skin (which is why smokers' complexions look yellow) and revs up the enzyme responsible for breaking down collagen (and that definitely leads to wrinkles), says Francesca Fusco, a dermatologist in New York City. Your skin can bounce back once you quit. "Within two weeks, you see improvements," she says. "The texture improves; it's a little smoother. Over time, the brightness comes back."