If you got your period early in life—also called early menarche—and/or went into menopause late, you’ve been exposed to the female reproductive hormones estrogen and progesterone for a long time. (These hormones are what regulate your periods.) This long-term exposure puts you at higher risk of breast cancer. According to the American Cancer Society, studies have found that women using oral contraceptives (birth control pills) have a slightly greater risk of breast cancer than women who have never used them, though the Pill has been shown to reduce risk of endometrial and ovarian cancers.
4. Exposure to hormones