Breasts are the same in men and women until puberty. During sexual maturity, a woman’s breast tissue grows in size and amount.

Women’s breasts consist of mammary glands, or the glandular tissue, that hold milk-producing cells. They also have connective tissue, which includes adipose (fatty tissue). These tissues make up the shape of your 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 diagnostic mammogram. It’s a type of X-ray. The mammogram will show what kind of tissues are dominant in your breasts.

Dense breasts are a risk factor for breast cancer. Other risk factors include:

  • being female
  • older age
  • smoking
  • a family history of breast cancer
  • certain genes, such as BRCA1 and BRCA2

Read on to understand how dense breasts are diagnosed and how it relates to your risk for breast cancer.

Learning the structure of a breast can help with understanding breast density.

The biological function of the breast is to make milk for breastfeeding. The raised area on the outside is the nipple. Surrounding the nipple is darker-colored skin called the areola.

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.

Glandular tissue

Glandular tissue consists of a complex network of structures designed to carry milk to the nipple.

This glandular part of the breast is divided into sections called lobes. Within each lobe are smaller bulbs, called lobules, which produce milk.

Milk travels through small ducts that come together and connect into larger ducts designed to hold the milk. The ducts end at the nipple.

Connective tissue

Connective tissue in the breast provides shape and support. Muscle tissue is present around the nipple and the ducts. It helps squeeze milk toward and out of the nipple.

There are also nerves, blood vessels, and lymphatic vessels. Breast tissue extends from the breastbone near the middle of the chest all the way to the armpit area.

The lymph vessels of the breast drain excess fluid and plasma proteins into lymph nodes. Most of this drainage goes into nodes in the armpit. The rest goes to nodes located in the middle of the chest.

Fatty tissue is the remaining component of breast tissue. The more fatty tissue a breast has, the less dense it’s considered to be.

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

Dense breasts are normal in many mammograms. According to a 2012 article in the Journal of the National Cancer Institute, nearly 40 percent of women in the United States have dense breasts. Factors that increase the likelihood of dense breasts are:

  • older age at first birth
  • fewer or no pregnancies
  • younger women
  • hormone therapy, especially combined estrogen and progestin
  • being premenopausal

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

Make an appointment 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.

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.

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 women with mostly fatty breasts.

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

Research also suggests women with dense breasts have more ducts and lobes. This increases their 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 suggests women with dense breasts who are considered obese or have tumors at least 2 centimeters in size have a lower breast cancer survival rate.

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

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.

But 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 cancers are missed in a mammography. That percentage can approach 40 to 50 percent in women with dense breasts.

Studies have also found that digital and 3-D mammograms are better for detecting cancer in dense breasts because digital images are clearer. Fortunately, these types of machines are becoming more common.

You can help reduce your risk of breast cancer by taking steps to live a healthy lifestyle. Examples include:

  • exercising regularly
  • refraining from smoking
  • limiting alcohol intake

It’s also recommended to eat healthy. But know that diets won’t affect your breast density, according to one study. 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 have 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 risks for breast cancer.

General guidelines include a mammogram every other year after you’re 45 years old.

Women in a high-risk breast cancer group and women using hormone therapy should also get a yearly MRI. MRIs can sometimes be more helpful in evaluating very dense breasts.

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.

If you do have dense breasts, your doctor may recommend regular mammograms. Early diagnosis affects the outcome of breast cancer. Your doctor may recommend yearly mammograms and MRIs if you have other risk factors for breast cancer.

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 women with dense breasts.

Find support from others who are living with breast cancer. Download Healthline’s free app here.