Maybe you’re reading up on breast cancer screening guidelines and see that 3D mammograms are often recommended for dense breast tissue. Or perhaps you just had your first mammogram, and your results say you have dense breasts. Either way, now you’re wondering: What is dense breast tissue? Is it normal?

Yes, dense breast tissue is normal. It’s also very common – about half of women have dense breasts. And unfortunately, it can be a risk factor for breast cancer.

Below, we explain what it means to have dense breasts, why it may slightly increase your risk of breast cancer and what to do about it.

What is dense breast tissue?

There are different types of tissues in your breasts. Dense breast tissue has more cells than non-dense tissue in the same amount of space.

Here’s a closer look at each type of tissue that make up your breasts, and if it’s considered dense:

  • Fatty tissue – This type of tissue is non-dense and fills in your breasts, making them soft.
  • Fibroglandular tissue – Glandular tissues are responsible for milk production, and fibrous connective tissues hold both fatty and glandular tissues in place. Together, they’re called fibroglandular tissue and considered dense tissue.

Aside from being a type of tissue within your breasts, dense breast tissue is often used to describe what dense breasts look like on a mammogram. Breast density is based on the amount of fibroglandular tissue compared to the amount of fatty tissue.

If you have a lot of fibroglandular tissue, your breasts are considered dense. Breast density is determined by a radiologist. Radiologists are medical doctors who are specially trained in medical imaging – making them experts in reading mammogram images.

Categories of breast density

Doctors categorize breast tissue density based on the Breast Imaging Reporting and Data System (BI-RADS®) developed by the American College of Radiology. These categories are based on the percentage of glandular or fibrous connective tissue that they see in your breasts and are typically listed as A-D.

Breast density category How much fibroglandular tissue? How many women have them? Considered dense?
Category A
Almost entirely fatty
25% 10% No
Category B
Scattered areas of fibroglandular density
25-50% 40% No
Category C
Heterogeneously dense which may obscure small masses
51-75% 40% Yes
Category D
Extremely dense, which lowers the sensitivity of the mammogram.
>75% 10% Yes

Causes of dense breast tissue

There are certain factors that can make it more or less likely that you’ll have dense breasts. Your risk factors can also change over time.

Reasons you’re more likely to have dense breast tissue

  • Genetics – Dense breast tissue is usually inherited. So if you have dense breasts, it’s very likely that you have a mother or sister who has them too.
  • Low body mass index – People who have a lower percentage of body fat are more likely to have dense breasts.
  • Postmenopausal hormone replacement therapy (HRT) – While some studies show that hormone replacement therapy may increase your chances of having dense breasts and breast cancer risk, data is conflicting and no definite increase has been proven. So, it’s best to talk with your doctor or clinician about the risks and benefits of HRT.
  • You’re pre-menopausal – If you’re under 50 years old and haven’t gone through menopause, you’re much more likely to have dense breasts. Up to 75% of women between the ages of 40-49 have dense breasts.

Is it possible to reduce breast density?

While certain factors can make it more likely that you’ll have dense breasts, there really isn’t anything you can do to change your breast density. For example, you can’t lower your breast density by changing what you eat or increasing how much you exercise.

Are there any symptoms of dense breasts?

No, there aren’t any symptoms of dense breasts. Dense breasts don’t look differently from the outside – they aren’t differently shaped, nor are they bigger or smaller than other breasts.

In fact, you probably won’t know if you have dense breasts until after you’ve had a mammogram – sometimes, dense breasts are actually called “mammographically dense breasts.”

How doctors use mammograms to determine breast density

A mammogram uses X-ray technology to capture images of the inside of breasts. Depending on the type of mammogram, either 2D or 3D images are created and reviewed by a radiologist. As we mentioned earlier, a radiologist is a medical doctor with special training in medical imaging.

Mammography images will show the inside of your breast in a combination of white and gray, just like other types of X-rays. Dense breast tissue has a white background, while less dense tissue shows as gray.

Using their expertise, the radiologist will typically report your tissue density in your mammogram results. In Minnesota, for example, all mammography providers are required by law to report breast density to patients with dense breasts.

Why breast density matters

There are two main reasons to care about your breast tissue density.

1. Dense breast tissue has a slightly higher risk of developing cancerous cells

For most women, breast density isn’t a major breast cancer risk factor. But since it’s not a risk factor you can change, it’s still important to be aware of.

If you have heterogeneously dense breasts, which is “Category C” on the BI-RADS® scale we mentioned earlier, your risk of breast cancer is 1.2 times the normal risk. If you have extremely dense breasts, which is “Category D”, your breast cancer risk doubles. But it’s important to know that while this increased risk may seem relatively high, the actual risk for breast cancer for women with extremely dense breasts is still low.

It’s also important to keep in mind that breast density isn’t the only factor that influences your breast cancer risk. Other risk factors such as age, family history, early menstruation, diet, alcohol use, obesity, lack of physical activity, radiation to the chest and hormone replacement therapy can also increase your risks.

2. Cancer may be harder to find in dense breasts

Dense breast tissue may make it more difficult to identify cancer with a mammogram and may be associated with a slight increased risk of breast cancer.

As we mentioned earlier, dense breast tissue has a white background on a mammogram. Cancer shows as a white spot or white dots on a mammogram. So, finding these white spots or white dots can be harder on a white background than on a gray background.

And while it may be slightly harder for mammography to detect cancer in dense breasts, regular screening mammograms are still recommended for women with dense breasts. Your primary care doctor or clinician, OB-GYN or other women’s health specialist can help you determine when or how often you should be screened based on your individual risk factors.

Find out if you have dense breasts (and screen for breast cancer)

The density of your breasts matters because it can increase your chance of developing breast cancer. Getting a mammogram is the best way to learn about your breast tissue density.

If you’re over 40 and haven’t gotten a mammogram, talk to your doctor about when you should start – your yearly preventive care visit is a great time to bring up the topic. If you’re due for a physical, schedule a preventive care appointment now.

Of course, if you’re ready to get a mammogram, there’s no need to wait. Most mammograms are women’s preventive screenings covered by insurance. But coverage depends on your specific plan. So, it’s a good idea to check to see how tests and screenings are covered by your insurance before scheduling your appointment.