Here's the problem with thin skin: It generally lacks some (or all) oil glands, which means it dries out quickly, and the barrier is easily compromised. "Pay special attention to eyes, neck and décolleté," says Engelman. "That skin is thinner and tends to be the first to show signs of aging."

And wrinkles on your chest or the backs of your hands will give away your age -- even if you've worked hard to keep your facial skin looking as young as possible. For amazing looking skin from head to toe, use your facial skin care routine anywhere that's exposed -- i.e. your neck, chest and hands -- and pay special attention to the delicate skin around your eyes.

Here's what scientists know for sure: What you put in your mouth will affect the way your skin looks and functions. Some myths are just that: myths. If you eat a French fry or a piece of chocolate, for example, you're probably not going to break out. But recent studies have uncovered a clear link between dairy and acne. And that same research applies to high glycemic foods in general -- so cake and cookies are equally dangerous to a clear complexion.

Fortunately, there are also skin-benefitting foods. Tomatoes, for example, are rich in lycopene, which boosts the skin's ability to protect itself from the sun. And foods loaded with omega fatty acids, like salmon and nuts, keep skin naturally moisturized and help maintain good barrier function. Meanwhile, antioxidant-rich foods like blueberries help the skin block damage-causing free radicals.

Many doctors say they can assess a patient's diet purely by looking at their skin. And the healthier you eat, the better your skin will look.

One of the best ways to keep your skin healthy: Kick that smoking habit. Research proves that smoking cigarettes breaks down collagen and elastin in the skin, leading to premature aging. And, according to the Mayo Clinic, there may be up to a 10-year delay before you see the damage. So quit now -- or be grateful you never started.