Late menopause. If you enter menopause after age 55, you're more likely to develop breast cancer. Experts attribute this risk to the prolonged exposure of the breast tissue to estrogen.

First pregnancy at older age. If your first full-term pregnancy occurs after age 30, or you never become pregnant, you have a greater chance of developing breast cancer. Although it's not entirely clear why, an early first pregnancy may protect breast tissue from developing genetic mutations that result from estrogen exposure.

Race. White women are more likely to develop breast cancer than black, Hispanic or Asian women, but black women are more likely to die of the disease because their cancers are found at a more advanced stage. Low-income women often don't receive the routine medical care that would allow breast cancer to be discovered earlier.

Hormone therapy. Treating menopausal symptoms with the hormone combination of estrogen and progesterone for four or more years increases your risk of breast cancer.

In addition, therapy with estrogen and progesterone can make malignant tumors harder to detect on mammograms, leading to cancers that are diagnosed at more advanced stages and that are harder to treat. Using estrogen alone hasn't been shown to increase breast cancer risk in post-menopausal women.

Birth control pills. Use of birth control pills is associated with an increased risk of breast cancer in pre-menopausal women. The risk seems to be greater for women who use birth control pills for four or more years before their first full-term pregnancy, but since delayed first pregnancy is also a risk factor, part of the risk could be attributed to that.

Overall, risk of breast cancer for users of birth control pills is small and appears to be confined to the short term. Risk levels return to normal within five to 10 years after discontinuing use.

Using birth-control pills also doesn't appear to further increase breast cancer risk in women with a family history of breast cancer or with a personal history of benign breast disease. Because this is an are of ongoing study, talk with your doctor about the latest information on the pill and breast cancer.

Smoking. Evidence is mixed on the relationship between smoking and breast cancer risk. Some studies show no like between cigarette smoking and exposure to secondhand smoke and breast cancer.

Others suggest that smoking increases breast cancer risk. Exposure to second-hand smoke and breast cancer risk remains an area of active research. Despite the controversy surrounding this issue, there are clear health benefits—other than minimizing breast cancer risk—to quitting smoking and limiting your exposure to second-hand smoke.