context: If you've had a mammogram recently, the doctor or technician may have told you that you have dense breasts. Radiologists in much of the U. S. are required by law to let you know if you fall into that category when they send your results. Having dense breasts is normal and very common. But you may be confused about what it means and what you should do about it. Breast density isn't something you can control. You don't need to treat it, and it often changes over time. It has nothing to do with how your breasts look or feel. It's about the way they appear on a mammogram. Breasts are made of fat and tissue that give them their shape, and glands and ducts that make milk. Fat appears dark on a mammogram. Everything else looks white. Measuring the density of your breasts is not an exact science. It's a judgment made by your radiologist. Based on what they see on the X-ray, they assign your breasts to one of four categories: Mostly fatty: Breasts have the least amount of fibrous tissue. Scattered areas of density: Most of the breast is fat, but some areas are dense. Heterogeneously dense: Most of the breast is dense tissue with some areas of fat. Extremely dense: The breasts have almost no fatty tissue. Women over age 40 are about evenly split between having dense and non-dense breasts, with most falling into one of the middle two categories (scattered or heterogeneous density.) Only about 10% of women have breasts that are either mostly fatty or extremely dense. Things that affect your breast density include: Age: Young women tend to have denser breasts than older women. Most women's breasts lose density as they age, though not always. Heredity: If your mother had dense breasts, you probably will, too. Menopause: Most women's breasts become more fatty after they go through menopause. Hormones: Hormone replacement therapy and birth control pills can make breasts more dense. Breastfeeding: Dense breast tissue is involved in milk production. It can make your breasts more dense. Dense breasts are harder to read on a mammogram. Tumors and masses show up as white spots just like dense tissue does. So it can be a challenge to tell the difference between what's normal and what's suspicious. It's easier to miss a trouble spot or to falsely diagnose breast cancer. That doesn't mean you should stop getting mammograms. Even in women with dense breasts, masses are correctly identified most of the time. And new digital technology has made mammograms more accurate. They may not be perfect, but mammograms are still the best way to detect breast cancer early. To catch breast cancer early, it's widely recommended that all women, regardless of their breast density, do monthly self-exams, get examined by a doctor annually, and have a mammogram starting at age 40. Having dense breasts does appear to increase your risk for breast cancer. But experts don't agree on whether high breast density alone means you should get extra cancer screening. You should talk with your doctor about your other risk factors. If you're also at a higher risk because of your age, race, family history, or previous biopsies, it may be a good idea to get tested more often or to have a different kind of test. These tests can find cancers that traditional mammograms may miss. Magnetic resonance imaging ( MRI): If you're at high risk of breast cancer, you'll typically be told to get an MRI along with a yearly mammogram. An MRI uses a magnetic field to create a picture of the inside of the breasts. Digital breast tomosynthesis ( DBT): This is a special kind of mammogram that takes pictures from different angles and puts them together to produce a 3- D image. Ultrasound : Technicians use sound waves to make images of the inside of the breast. Breast-specific gamma imaging: Radioactive material is injected into the bloodstream, then detected with a special camera. It appears different in cancerous tissue compared with normal tissue. The drawback of extra tests is that they often turn up things that aren't cancer. That can lead to more tests or even surgery that you may not need. Your insurance may not cover the cost of these tests, so make sure to check first. A mammogram is the only kind of breast screening test proven to save lives. Talk with your doctor, and together you can decide which tests are right for you.