What Does Skin Do?

Q. I saw a dermatologist recently because an old mole seemed to be getting larger. The mole turned out to be fine, but on the way home I had what you may think is a crazy question: What does skin do? What is its job?
-- Kerry, NYC

A. We YOU Docs get asked lots crazier questions than that. (Watch Dr. Oz's show any weekday!) Sometimes it seems like the main purpose of skin is to sell magazines and movie tickets, but its real job is to protect your most valuable assets from the outside world: your heart, brain, bones, blood, nerves, muscles, the works. It also wraps them up in a nice-looking package so you're not a blobby organism.

In addition, skin is your first line of defense against infection. It fends off millions of germs, chemicals, and other contaminants that are out to invade you. It helps regulate your body temperature and, of course, lets you touch and be touched, so you sense pain ("Ouch, that's hot!"), feel pleasure, and express love. (Your skin's good to you. Be good to it. Avoid these 5 common skin irritants.)

Skin does one more genius thing: When the sun shines on it, your skin makes vitamin D3, the ultimate antiaging vitamin. It's essential for keeping your heart, bones, memory, and blood pressure humming along.

Get personalized skin-care advice for your one-of-a-kind skin. Take the SkinCare quiz.