19. What's a sure way to stay cancer-free?
There isn't one. The ugly truth is, some people who do everything right get cancer anyway. Still, bad habits worsen your odds. Tobacco use causes about one in three cancers overall, and diet, inactivity, and obesity contribute to another third of cases, says Peter Greenwald, MD, PhD, director of the division of cancer prevention at the National Cancer Institute.

20. Do I really need to lift weights? Isn't yoga enough?
Yoga can build muscle, exercise physiologists say, as long as your muscles burn a little; poses like downward dog require you to lift and shift your own body weight. It's less clear whether yoga can build or maintain bone density—a benefit weight lifting confers—simply because it hasn't been studied. If your current yoga sessions don't feel challenging, or if your bones are thinning, consider adding strength training to the weight-bearing exercise (walking, for example) that you're already doing for your bones. (You are already doing it, right?)

21. Do self-tanners cause cancer?
Nope. The faux glow is delivered by dihydroxyacetone (DHA), which only interacts with dead surface cells on the skin to create a color change that simulates a tan for five to seven days. However: "Although self-tanners do not cause cancer, they generally don't give any protection against UVB or UVA, so it's still important to use sunscreen to prevent aging, sun damage, and skin cancer," says Oanh Lauring, MD, a dermatologist at Mercy Medical Center in Baltimore.

22. Skip exercise when I have a cold, right?
Not necessarily. "If the symptoms are above the neck, like a runny or stuffy nose, sneezing, or sore throat, exercising should pose little or no risk," says Cedric X. Bryant, PhD, chief science officer for the American Council on Exercise in San Diego. "In fact, mild to moderate exercise has been shown to help boost immune system function." But if your symptoms include body aches, chest congestion or tightness, and a hacking cough, workouts should be postponed.