A risk factor is anything that may increase your chance of having a disease. Risk factors for a certain type of cancer might include smoking, diet, family history, or many other things. The exact cause of someone's cancer may not be known. But risk factors can make it more likely for a person to have cancer.

Things you should know about risk factors for cancer:

• Risk factors can increase a person's risk, but they do not necessarily cause the disease.
• Some people with one or more risk factors never develop cancer. Other people can develop cancer and have no risk factors.
• Some risk factors are very well known. But there is ongoing research about risk factors for many types of cancer.

Some risk factors, such as family history, may not be in your control. But others may be things you can change. Knowing the risk factors can help you make choices that might lower your risk. For example, if an unhealthy diet is a risk factor, you may choose to eat healthy foods. If excess weight is a risk factor, your doctor may check your weight or help you lose weight.

Risk factors for breast cancer include:

• Your sex. Breast cancer in women is much more common than in men.
• Race or ethnicity. White people develop breast cancer slightly more often than African-American people. But African-American people tend to die from breast cancer more often. This may be due to differences in access to medical care. This may also be partly due to the fact that African-American people often have a more aggressive type of tumor. (Aggressive tumors grow and spread quickly.) Why this happens is not known. The risk of having breast cancer and dying from it is lower in people who are Hispanic, American Indian, or Asian.
• Older age. Most people with breast cancer are older than age 55.
• History of breast cancer. If you've had cancer in one breast, you're at an increased risk of having it in the other breast or another part of the same breast.
• Past chest radiation for another cancer. If you've had high-dose radiation therapy to your chest, you have an increased chance for breast cancer. The risk is even higher if it happened when you were a child or teen. It's important to remember that radiation therapy involves high doses of radiation. The small doses used for breast cancer screening do not increase your risk.
• Family history. Having a parent, sibling, or child with breast cancer increases your risk.
• Benign breast disease. People with certain noncancer (benign) breast conditions, such as hyperplasia or atypical hyperplasia, may have an increased risk for breast cancer. The only way to know if you have benign breast disease and what kind is by having a biopsy.
• Lobular carcinoma in situ (LCIS). LCIS is a noninvasive growth of abnormal cells in the lobules of the breasts (milk-producing glands). LCIS is not considered cancer. But it increases the risk of getting breast cancer. LCIS is typically diagnosed from a biopsy that is done on the breast for another reason.
• DES (diethylstilbestrol) exposure. People who took this medicine while pregnant to lower the chance of miscarriage are at higher risk. People whose birth parent took DES during pregnancy with them may also have a slightly higher risk.
• Early menstrual periods. People whose periods began before age 12 have a slightly higher risk for breast cancer.
• Late menopause. People are at a slightly higher risk if they began menopause after age 55.
• Not giving birth to a child, not breastfeeding, or giving birth to your first child after age 30. These people have a slightly higher breast cancer risk.
• Dense breast tissue. People whose breasts have larger areas of dense tissue on mammograms are at increased risk for breast cancer.
• Drinking alcohol. Breast cancer risk goes up if you drink just 1 glass of wine, beer, or a mixed drink a day. The more you drink, the higher your risk. It's best not to drink alcohol. If you chose to drink, limit yourself.
• Long-term use of estrogen and progestin medicines after menopause. This is known as hormone replacement therapy (HRT). The hormones are most often used together. The longer you've used HRT, the higher your risk. If you stop taking the medicines, your risk should go back down to normal after 5 years. If you decide to use HRT, use it at the lowest dose and for the shortest time possible.
• Excess weight, especially after menopause. This risk factor is complex. Research shows conflicting results about the link between weight and breast cancer. Overall, your risk of breast cancer is lower if you stay at a healthy weight with a body mass index below 25. If you're overweight and you get breast cancer, the excess weight also affects your chances of being cured. And it affects your chances of the cancer coming back after treatment.
• BRCA1 and BRCA2 genes. Certain inherited changes in genes are another risk factor. Hereditary breast cancer accounts for about 1 in 20 to 1 in 10 breast cancer cases. BRCA1 and BRCA2 genes are the most common genes linked to breast cancer. These are tumor suppressor genes that usually have the job of controlling cell growth and cell death. When they're changed, they don't do their job correctly, and cancer tumors may grow. Changes in these genes account for most cases of hereditary breast cancer. They're linked to other kinds of cancer, especially ovarian cancer. In the U.S., BRCA changes are most common in women of Ashkenazi Jewish ancestry.

There are other, less common genes that can impact breast cancer risk.

Talk with your doctor about your risk factors for breast cancer and what you can do about them. There are different tools that can be used to help estimate your risk. These can help you to set up your own best prevention and screening plan.