Breasts are the same in everyone until puberty. During sexual maturity, female breast tissue grows in size and amount.

Female breasts consist of glandular tissue which includes the glands and ducts that produce and carry milk to the nipple. They also have connective tissue, which includes adipose (fatty tissue). These tissues make up the shape of breasts.

Your breasts won’t necessarily feel different if they’re dense. The only way to know if you have dense breasts is through a mammogram. It’s a type of X-ray. The mammogram will show what kind of tissues are dominant in your breasts.

Having dense breasts is a risk factor for breast cancer. Other risk factors include:

  • age, as most breast cancers are diagnosed after age 50
  • smoking
  • having diabetes or obesity
  • a family history of breast cancer
  • certain genes, such as BRCA1 and BRCA2
  • exposure to hormones for longer periods of time, such as starting menstrual periods before age 12 and later menopause after age 55
  • using hormonal birth control or hormone therapy after menopause
  • not having given birth
  • having had ovarian or uterine cancer
  • having had benign breast conditions such as hyperplasia, complex fibroadenoma, and papillomatosis
  • undergoing radiation therapy for other conditions before age 30

Read on to understand how dense breast tissue is diagnosed and how it relates to the risk of breast cancer.

Language matters

We use the term “women” and “female” in this article to refer to sex assigned at birth and reflect terms historically used to gender people.

Sex and gender exist on spectrums and your gender identity may not align with these terms. Your doctor can better help you understand your specific circumstances.

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The biological function of the breast is to make milk for breastfeeding. Inside the breast is glandular, fatty, and connective tissue. A system of lymph nodes, called the internal mammary chain, runs through the center of the chest.

You can’t tell if breast tissue is dense by feeling it. Breast density describes the relative amount of these various tissues that can only be seen on a mammogram or other breast imaging.

For breasts to be considered dense, they need to show higher amounts of connective tissue and glandular tissue than fatty tissue.

Having dense breasts is common, with about 50 percent of those who get mammograms showing dense breast tissue.

After menopause, breasts are typically composed more of fat than other connective and glandular tissue. This is because the number and size of milk-producing glands decreases after menopause.

Increased risk for cancer

Some studies have shown that women with extremely dense breasts have a four to six times greater risk of developing breast cancer than those with mostly fatty breasts.

Cancer appears to develop in areas where the breast is dense. This suggests a causative relationship. The exact connection is unknown, though.

A 2018 study found that dense breasts were associated with larger tumor diameter and more lymph node-positive disease than non-dense breasts.

Research also suggests that dense breasts have more ducts and glands. This increases risk because cancer often arises in these places. Researchers are still studying this theory.

Dense breasts don’t affect other outcomes, such as survival rates or response to treatment. However, one study suggested that women with dense breasts who are considered to have obesity or have tumors at least 2 centimeters in size have a lower breast cancer survival rate.

Keep in mind that having dense breasts doesn’t necessarily mean you have breast cancer.

Missed readings

Traditionally, doctors use mammography to diagnose potentially harmful lesions in the breasts. These lumps or lesions usually appear as white spots against black or gray areas.

If you have dense breasts, that tissue will appear white as well. This makes it more difficult for doctors to see potential breast cancer.

According to the National Cancer Institute, about 20 percent of breast cancers are missed in mammography. That percentage can approach 40 to 50 percent in dense breasts.

3D mammograms are the preferred method for detecting cancer in dense breasts because digital images are clearer. Fortunately, these types of machines are becoming more common.

Those with dense breasts may be requested to undergo MRI screenings or breast ultrasounds if a mammogram is difficult to interpret.

Dense breasts are normal in many mammograms. You may have a higher likelihood of dense breasts if you:

  • were older when giving birth the first time
  • have had few or no pregnancies
  • are in premenopause
  • use or have used hormone therapy, especially combined estrogen and progestin

Dense breasts can have a genetic component. Your chances of having dense breasts increase if your mother has them, too.

Talk with your doctor if you’re concerned about dense breasts and your risk for breast cancer.

When radiologists look at your mammogram, breast tissue will show up as black and white. Glandular and dense connective tissue will show up white on a mammogram because X-rays don’t pass through as easily. This is why it’s called dense tissue.

X-rays pass through fatty tissue easier, so it shows up black and is considered less dense. You have dense breasts if your mammogram shows more white than black.

These tests are also used to help doctors diagnose potential breast cancer:

While most people may only get film or digital mammograms, additional diagnostic tools may also be recommended based on your medical and family history, genetics, existing medical conditions, and tests available to you. Your doctor can help you determine which will work best for you.

A classification system known as the Breast Imaging Reporting and Database Systems (BI-RADS) Breast Composition Categories recognizes four categories of breast composition:

BI-RADS composition categoryBreast tissue descriptionAbility to detect cancer
A: mostly fattymostly fatty tissue, very few glandular and connective tissuescancer will likely show on scans
B: scattered densitymostly fatty tissue with few foci of connective and glandular tissuecancer will likely show on scans
C: consistent densityeven amounts of fatty, connective, and glandular tissue throughout the breastsmaller cancer foci are difficult to see
D: extremely densesignificant amount of connective and glandular tissuecancer may blend in with tissue and be difficult to detect

Ask your doctor about the BI-RADS results related to your breast tissue density when you get your mammogram results.

You can help reduce your risk of breast cancer through lifestyle measures. Examples include:

  • exercising regularly
  • refraining from smoking
  • limiting alcohol intake

It’s also recommended to eat a nutrient-dense diet when you can. Older research suggests, though, that diet won’t affect your breast density. Researchers found no link between breast density and:

  • carbohydrates
  • crude and dietary fiber
  • total protein, including animal
  • calcium
  • caffeine

Many states, including California, Virginia, and New York, require radiologists to tell you if your breasts are extremely dense.

While having dense breasts doesn’t necessarily mean you will develop breast cancer, knowing you have dense breasts is a step toward health awareness. Ask your doctor to suggest a screening plan if you have dense breasts or other risk factors for breast cancer.

The United States Preventive Services Task Force recommends a mammogram every 2 years for those between 50 and 70 years old. Early screening or other diagnostic tests may be recommended from ages 40 to 49 depending on personal risk factors.

It’s suggested that breast cancer develops in areas where the breast is dense. However, more research is needed to see if there’s a direct relationship. Dense breasts mainly increase your risk for a missed diagnosis.

That’s because it’s harder for doctors to spot tumors on mammography. Dense breast tissue and tumors both show up white. Fatty breast tissue shows up as gray and black.

Keep in mind that studies define increased risk by comparing women with the highest breast density to women with the lowest density. The risks don’t necessarily apply to everyone across the board. Dense breasts are a common finding in many mammograms.

If you want to read the latest research and recommendations, the nonprofit organization Are You Dense? advocates for people with dense breasts.