Studies show that starting oral contraceptives before the age of 18 may result in a tripled lifetime risk of breast cancer — perhaps because the synthetic hormones impede the action of the real ones. And if, at menopause, you're being sold a regimen of hormone replacement therapy (HRT), consider this: HRT may induce breast lumps and breast cancer, according to a recent JAMA study.

More Know-5 Facts: Find out what you need to know about heart health, emotional health, colon health and bone health.

Message Boards: Talk to others about breast health >>