Most cases of invasive breast cancer—cancer that has grown beyond the layer of cells where it began—occur in women 55 and older.

Source: American Cancer Society

Your risk for breast cancer increases if others in your family—on either your mother’s or father’s side—also had the disease. The risk is about doubled if your mother, sister or daughter was affected

Source: American Cancer Society

Women who have dense breasts—breasts that have more glandular tissue and less fatty tissue—have an elevated risk for breast cancer.

Source: American Cancer Society

Some, but not all, noncancerous breast conditions increase breast cancer risk. If you’ve been diagnosed with a benign breast problem, it’s important to speak with your doctor about whether it could affect your chances for developing cancer.

Source: American Cancer Society

Your risk for breast cancer may be slightly higher than that of other women, possibly because you’ve had a greater lifetime exposure to the hormones estrogen and progesterone.

Source: American Cancer Society

Mutations in these genes, which normally help prevent uncontrolled cell growth, may be inherited. These mutations greatly increase breast cancer risk. However, there are options for managing this risk. Your doctor can tell you more about them.

Source: American Cancer Society

Women who are using birth control pills have a slightly higher risk of getting breast cancer than women who have never used them. However, after 10 years without the pills, the increased risk seems to disappear.

Source: American Cancer Society

Women who have not had children or who had children later in life have a slightly higher risk of getting breast cancer than women who had children earlier. One reason for this may be that pregnancy reduces the number of menstrual cycles a woman has in her lifetime.

Source: American Cancer Society

Some evidence suggests breastfeeding may slightly lower your risk of developing breast cancer, especially if you do so for 1 1/2 to 2 years. This may be because breastfeeding lowers a woman’s total number of menstrual periods.

Source: American Cancer Society

Combined hormone therapy has been shown to increase breast cancer risk. The risk may return to normal within five years of stopping the therapy. Use of estrogen alone does not seem to pose a similar danger, but because it does increase the risk of endometrial cancer it is only used in women who do not have a uterus.

Source: American Cancer Society

Carrying excess weight—at least after menopause—seems to raise breast cancer risk. That’s particularly true if the weight is mostly around your waist.

Source: American Cancer Society

Drinking alcohol regularly—even just one drink a day—increases breast cancer risk. The more you drink, the greater the risk.

Sources: American Cancer Society; National Cancer Institute

Though it isn’t clear how much exercise is most beneficial, regular physical activity—such as brisk walking—can reduce your chances for developing breast cancer.

Source: American Cancer Society

At one time, diethylstilbestrol was given to women to reduce the risk of miscarriage. It hasn’t been prescribed in the U.S. since 1971. But research has shown that women who once took the medication have a slightly increased breast cancer risk. Some evidence suggests the risk may carry over to children exposed in the womb.

Source: American Cancer Society

Radiation treatment to the chest for an earlier cancer significantly increases your chances for developing breast cancer later. Risk appears to be greatest if you received treatment in your teens. Treatment given after age 40 does not seem to pose the same danger.

Source: American Cancer Society

People who have a history of breast cancer are more likely to get the disease again.

Source: National Cancer Institute