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 1 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 healthcare provider may check your weight or help you lose weight.

Risk factors for breast cancer include:

• Gender. Breast cancer occurs about 100 times more often in women than in men.

• Race or ethnicity. White women develop breast cancer slightly more often than African-American women. But African-American women tend to die of breast cancer more often. This may be partly due to the fact that African-American women often have a more aggressive type of tumor. (Aggressive tumors grow and spread quickly.) Why this happens is not known. The risk for having breast cancer and dying from it is lower in women who are Hispanic, Native American, or Asian.

• Older age. Most women with invasive cancer are over 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 to your chest, you have an increased chance of 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. Women with certain noncancer (benign) breast conditions such as hyperplasia or atypical hyperplasia have an increased risk of breast cancer. The only way to know if you have benign breast disease and what kind it is by having a biopsy.

• DES ( diethylstilbestrol) exposure. Women who took this medicine while pregnant to lower the chance of miscarriage are at higher risk. Women whose mothers took DES during pregnancy may also have a slightly higher risk. 

• Early menstrual periods. Women whose periods began before age 12 have a slightly higher risk of breast cancer.

• Late menopause. Women are at a slightly higher risk if they began menopause after age 55.

• Not giving birth to a child, or giving birth to your first child after age 30. These women have a slightly higher breast cancer risk.

• Dense breast tissue. Women whose breasts have larger areas of dense tissue on mammograms are at increased risk for breast cancer. 

• Recent use (within 10 years) of birth control pills. Taking birth control pills slightly increases your breast cancer risk compared with women who have never used them. The risk may go back to normal over time after the pills are stopped.

• 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. Limit yourself to less than 1 drink per day.

• 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 (BMI) 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 5% to 10% of all 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 healthcare provider 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.