Dense breasts are made up of a higher amount of dense fibrous and glandular tissue compared to fat tissue. You can’t tell that you have dense breasts by the way your breasts look or feel, but a mammogram can show you if you have high or low breast density.
The three tissues in your breasts that make up your breast density include:
The amount of connective, glandular and fatty tissue in the breasts varies from person to person. And a wide range of breast density—from low to extremely dense—is normal. However, knowing that you have high breast density and understanding what it means for your care is helpful. That way, you can take steps to protect your breast health.
Doctors use four categories to describe whether you have dense breast tissue and the amount of breast density. These categories are based on how much tissue can be seen on your mammogram images. Dense breast tissue is very common, and as many as half of people who get a mammogram are told they have heterogeneously dense or extremely dense breasts.
A: Almost entirely fatty. This means your breast is almost all fatty tissue, typical in about 10% of people.
B: Scattered fibroglandular density. Scattered areas of glandular and fibrous connective tissue are found throughout your breasts, but there is still a higher amount of fat tissue. This type is found in about 40% of people.
C: Heterogeneously dense. You have fibrous and glandular evenly throughout your whole breast, meaning your breasts are mostly dense. About 40% of people are in this category.
D: Extremely dense. You have a very high breast density, meaning most of your breast tissue is dense. Extremely dense breasts are found in about 10% of people.
How much dense breast tissue you have is affected by many factors, such as your age, weight and hormones, including synthetic hormones taken as part of care for breast cancer or menopause. In general, dense breasts are more common in younger and leaner people.
The changes in your hormone levels when you reach menopause—or the end of your menstrual cycle—cause many effects on your body. After menopause, the dense fibrous connective and glandular tissue in your breasts usually decreases. That means you’re more likely to have less dense breast tissue after menopause.
This decline in dense breast tissue happens in those who go through menopause naturally and in people who have their ovaries removed with surgery, which causes early menopause. When you use hormone replacement therapy (HRT) for menopause, it may slow down this process of decreasing breast density. As a result, people who take HRT are more likely to continue having dense breast tissue until they stop HRT.
Breast density is important because high-density breasts makes it harder to see breast cancer and other conditions on a mammogram. This is because both breast cancer and dense breast tissue appear white on the images, making it difficult to distinguish between them. It’s also important because having dense breasts increases your risk of breast cancer.
Because dense breasts can’t be felt or seen, you won’t know how dense your breast tissue is until you have a mammogram. Breast density shows up in a range on mammography images— from mostly see-through fatty tissue to very dense tissue that appears white.
To help you be informed about your breast health and density, the Food and Drug Administration (FDA) requires every imaging provider in the country, including our imaging centers, to give you information about your breast density after a mammogram.
With this important information, you can talk with your doctor about what your breast density category means for your health. If you have heterogeneously dense or extremely dense breasts, ask about additional imaging tests or care to help check for signs of breast cancer and give you peace of mind.
