You can often get an idea of how old someone is by looking at his or her face — specifically the skin. As people age, it's normal to get wrinkles. And a person who has spent a lot of time in the sun, at tanning salons, or smoking cigarettes might have a lot of them.

The skin is made up of three layers:

1. the outermost layer everyone can see, called the epidermis (say: eh-puh-DUR-mis)
2. the middle layer, called the dermis (say: DUR-mis)
3. the innermost layer, called the subcutaneous (say: sub-kyoo-TAY-nee-us) layer

When we're young, we don't have wrinkles because the skin does a great job of stretching and holding in moisture. The dermis has an elastic quality thanks to fibers called elastin that keep the skin looking and feeling young. A protein in the dermis called collagen (say: KAHL-uh-jun) also plays a part in preventing wrinkles.

But over time, the dermis loses both collagen and elastin, so skin gets thinner and has trouble getting enough moisture to the epidermis. The fat in the subcutaneous layer that gives skin a plump appearance also begins to disappear, the epidermis starts to sag, and wrinkles form.

There's not a magic age (like 40) when everyone suddenly gets wrinkles. Some people in their 20s have little wrinkles around their eyes (called "crow's feet") from squinting or spending too much time in the sun.

Other people may be in their 50s or 60s before you can even see a wrinkle. This is usually because they have taken good care of their skin over the years and may have more sebum (say: SEE-bum), the skin's natural oil. They may also have "good genes" — which means their family members don't have many wrinkles.

Eventually, however, everyone will have at least a few wrinkles. It's a natural part of aging.

Here are some ways to prevent getting many wrinkles at an early age:

• Avoid spending too much time in the direct sun, especially during the hours when the sun's rays are harshest (between 10 a.m. and 4 p.m.). Ultraviolet (UV) rays cause many wrinkles. Sunblock helps, but it doesn't block out all the damaging UV rays that cause wrinkles to the skin. Still, if you are outside a lot, be sure to wear a sunblock with sun protection factor (SPF) 15 or higher and reapply often (every 2 to 3 hours). Always reapply after swimming or playing sports that make you sweaty!
• Don't go to the tanning salon. The UV light from tanning booths is just as damaging as the sun's — and sometimes worse.
• Don't smoke! Smoking robs your skin of precious moisture and causes premature (early) wrinkles. (Did you ever notice that most heavy smokers have wrinkles around their mouths?)
• Drink water.
• Moisturize dry skin, especially during months when the air is drier.