What is dense breast tissue?
Breasts are made of a combination of fatty tissue and fibroglandular tissue. Fibroglandular tissue is composed of milk ducts, lobules, and connective tissue. Fibroglandular tissue is more dense than fatty tissue and looks “dense”, or white, on a mammogram. Breast density refers to how much dense breast tissue is present on a mammogram compared to the amount of fatty tissue.
How will I know that I have dense breast tissue?
The density of your breasts is decided on a mammogram. You can't tell if your breast tissue is dense by doing a physical exam. Density may change throughout your lifetime. There is no relationship between breast size and density.
There are four categories used to describe breast density (ordered from least dense to most dense).
A: Almost entirely fatty
B: Scattered fibroglandular tissue
C: Heterogeneously dense
D: Extremely dense
The radiologist determines which category of breast tissue you have and includes it in your mammogram report. Women with the two highest categories of breast density (categories C and D) are considered to have dense breasts.
How common is dense breast tissue?
Dense breast tissue is very common and normal. Approximately 40 to 50 percent of women have dense breast tissue (categories C and D).
What causes dense breast tissue?
Breast tissue density is determined by many factors including your inheritable traits, age, certain hormonal medications, and other factors. It is important to know that dense breast tissue may change over time.
Dense breast tissue and screening for breast cancer
Both dense tissue and cancer appear white on a mammogram, which can make it more difficult to detect breast cancer on a mammogram when a woman has dense breasts. Higher breast density has also been shown to slightly increase the risk of breast cancer.
A mammogram is the best way to detect cancer as early as possible, even in women with dense breasts. Mammography is the only proven screening method to decrease risk of dying from breast cancer, regardless of breast density. An advanced type of mammogram called digital breast tomosynthesis (DBT), sometimes also called 3-D mammograms, improves detection of breast cancer, including in women with dense breast tissue. Mammograms are recommended for screening for breast cancer every one to two years starting at age 40 for those at average risk.
Supplemental screening, is a term to describe other tests (in addition to a mammogram) that improve early detection of breast cancer, including women at elevated- risk for breast cancer and women with dense breast tissue.
Women that are at elevated risk for breast cancer may need to start screening much earlier than age 40. Discuss your individual breast cancer risk factors and screening tests with your provider. UW Health also offers evaluation at the PATHS (Prevention, Assessment and Tailored Health Screening) Clinic for women that may be at elevated risk for breast cancer.
For women who are at elevated risk for breast cancer, breast MRI is often used as an additional screening test in addition to mammography to increase the detection of breast cancer.
Because mammograms are more limited in women with dense breasts, some women who are not at elevated risk for breast cancer but have dense breasts will choose to have supplemental screening in addition to a mammogram. UW Health in Madison offers abbreviated breast MRI as an additional test for these interested women. If you are interested in abbreviated breast MRI as an additional screening test because you have dense breasts, talk to your provider.
Watch a video about dense breast tissue and screening for breast cancer.
Breast density notification (federal requirement)
Federal regulations under the Mammography Quality Standards Act (MQSA) require all health care providers performing mammography in the U.S. to inform patients of their breast density following a mammogram. This national requirement ensures that individuals with dense breast tissue (categories C and D) receive clear information about how density may affect mammogram sensitivity and their personal breast cancer risk.
Below is the notification that patients with dense breast tissue receive:
“Breast tissue can be either dense or not dense. Dense tissue makes it harder to find breast cancer on a mammogram and also raises the risk of developing breast cancer. Your breast tissue is dense. In some people with dense tissue, other imaging tests in addition to a mammogram may help find cancers. Talk to your healthcare provider about breast density, risks for breast cancer, and your individual situation.”
Gail’s Law
Gail’s Law passed the Wisconsin legislature in February 2026 and was signed by the governor in March 2026. Gail’s Law supports insurance coverage for women at elevated risk for breast cancer and women with dense breasts who need additional tests such as breast MRI to evaluate for breast cancer. Gail’s Law does not start to take effect until July 1, 2026 , and insurance companies are not required to cover the new services until policy years starting Jan. 1, 2027. For 2026, coverage depends on your specific insurance plan. Patients who are interested in supplemental screening with breast MRI should contact their insurance providers to see if they cover these services.