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.