Breast cancer is shockingly common: About 1 in 8 women will face it during the course of their lifetime. What’s more, rates are climbing fastest among women under 50, according to the American Cancer Society—and even under 40 in some cases—which begs the question: Should you start screening based on your risk, not just the general rulebook?

Family history, genetics and even reproductive milestones play an important role in your risk of developing breast cancer. But not all risk factors carry the same weight—and many are beyond your control.

“Most women who are diagnosed with breast cancer have no family history of the disease and no known genetic variants linked to the condition,” said Lindi Vanderwalde, MD, a surgical breast oncologist at Cedars-Sinai in Marina del Rey. “At the same time, some women with clear genetic risk factors never develop breast cancer.”

In every case, the more you know about your personal risk factors, the better equipped you’ll be to sidestep the disease—or at least catch it during the earliest stages when it’s most treatable.

Scientists measure risk in two ways: absolute risk and relative risk.

Absolute risk describes the chance that something will happen (in this case, breast cancer) over a set time period. You might have heard the commonly cited statistic that 1 in 8 women will be diagnosed with breast cancer during their lifetime. That’s absolute risk. It comes from estimates showing that the average 35-year-old woman in the U.S. without any known risk factors for breast cancer has a 12.9% chance (about 1 in 8) of developing breast cancer by age 90.

Relative risk compares risk between two groups. For example, studies show that women who don’t exercise have a 25% higher risk of breast cancer compared to women who exercise regularly. Relative risk helps researchers understand how lifestyle, environment and other factors influence the likelihood of developing the disease.

“Your individual breast cancer risk may be higher or lower than the average absolute risk (12.9%), depending on your genes, family history and lifestyle,” said Ann Callahan, MD, a surgical oncologist at Cedars-Sinai in Torrance.

Read: How Do Your Genes Fit? Cracking the Code on Breast Cancer Risk

Some breast cancer risk factors are biological or historical: You can’t change them, but you can use them to make informed decisions about your screening and prevention strategy. These include:

• Age: Your risk of breast cancer increases with age. Most breast cancers are diagnosed in women over 50.
• Genetic variations: Certain genetic variants, including BRCA1 and BRCA2, increase your risk of developing breast cancer and other cancers.
• Family history: A strong family history of breast or ovarian cancers increases risk, even in the absence of a known genetic variant linked to the condition. 
• Breast density: Dense breast tissue not only is associated with a slightly increased risk of breast cancer but also makes it more difficult to detect breast cancer on a mammogram.
• Radiation exposure: Radiation therapy to the chest or breasts before age 30 increases breast cancer risk.
• Reproductive history: Early menstruation (before age 12), late menopause (after age 55), and pregnancy after age 30 or never becoming pregnant are all linked to increased breast cancer risk.
• Personal breast cancer history: People who have had breast cancer are more likely to get breast cancer a second time.
• Atypical cells on breast biopsy: Breast tissue that has abnormal features, even if it’s not cancer, is associated with an increased risk of breast cancer.

• Alcohol use: The more alcohol you drink, the higher your risk of developing breast cancer.
  Do this: Limit or avoid alcohol.
• Weight: Women who are overweight or obese have a higher breast cancer risk than women who maintain a normal weight.
  Do this: Maintain a healthy weight through balanced nutrition and regular exercise. Studies show that even modest, sustained weight loss—shedding just 5% of your body weight—reduces breast cancer risk in postmenopausal women with obesity or a higher body mass index (BMI).
• Physical inactivity: People who do not exercise regularly have a higher risk of developing breast cancer compared to those who are physically active.
  Do this: Aim for at least 150 minutes of moderate-intensity exercise each week or 75 minutes of vigorous activity.
• Hormone exposure: Taking estrogen and progesterone together for five years or more increases breast cancer risk. Certain oral contraceptives may also increase breast cancer risk.
  Do this: If you’re concerned about your breast cancer risk, talk to your doctor about the risks and benefits of menopause hormone therapy.
• Stress: While research is ongoing, chronic stress may indirectly affect breast cancer risk by influencing lifestyle factors such as sleep, diet and alcohol use.
  Do this: Manage high stress through mindfulness, counseling, social support and exercise.

Read: What Does It Mean to Have Dense Breasts?

Breast cancer risk-assessment tools rely on statistical models to estimate a woman’s risk of developing breast cancer based on her responses to a series of questions related to her medical history, reproductive history and family history.

Two commonly used tools include the Gail Model and the Tyrer-Cuzick Risk Assessment Calculator. Both are free and available online. 

“Risk calculators are a useful starting point, but they don’t tell the whole story,” said Vanderwalde. 

In fact, some women with high risk estimates never get breast cancer and others who have very low risk estimates do develop the disease. 

If your calculated lifetime risk is greater than 20%, talk with your physician about enhanced screening options, such as breast MRI or breast ultrasound in addition to mammography.

Read: A Clinic for Ovarian Cancer “Previvors”

The U.S. Preventive Services Task Force recommends all women at average risk of breast cancer begin breast cancer screening at age 40. 

“While guidelines differ on how often to screen, I recommend annual mammograms for all women beginning at age 40, regardless of their risk score,” said Callahan. 

If your risk of breast cancer is higher than average, your doctor may suggest additional steps to stay ahead of the disease, including: 

• Earlier screening. Doctors typically recommend screening 10 years before the youngest breast cancer diagnosis in your family.
• More frequent or advanced imaging, such as annual mammograms plus breast MRI.
• Genetic counseling and or genetic testing for personalized prevention strategies.
• Preventive medications, such as tamoxifen, raloxifene or aromatase inhibitors, when indicated.

Most importantly, make choices that support breast and whole-body health: Eat whole foods, exercise regularly, limit alcohol, manage stress and get sufficient rest. 

“Knowledge is power,” Vanderwalde said. “When you understand your risk, you can make proactive decisions that put you in the driver’s seat of your health and your future.”