Dense breasts and screening: what density means and what to ask

A mammogram letter that mentions dense breasts can be alarming. This page explains what density is, how it is graded, how common it is, why it matters, what extra tests are discussed and what to ask your doctor.

Screening policy differs between countries and between people. Your own doctor or screening service has the final word, and guidance can change.

What breast density is

Breasts contain glandular tissue, fibrous connective tissue and fat. The National Cancer Institute (NCI) says breast density describes the relative amount of these tissues as seen on a mammogram, and that dense tissue has relatively high amounts of glandular and fibrous tissue and relatively low amounts of fat.11National Cancer Institute: Dense Breasts: Answers to Commonly Asked Questions Defines breast density as seen on a mammogram. The American Cancer Society adds that it is unrelated to breast size or firmness.22American Cancer Society: Breast Density and Your Mammogram Report Last revised September 2024; density is not related to size or firmness.

This means density cannot be felt. According to the NCI, dense breast tissue cannot be felt by a woman during a self-exam, or by her doctor during a clinical breast exam, and only a radiologist looking at a mammogram can tell.11National Cancer Institute: Dense Breasts: Answers to Commonly Asked Questions Dense tissue cannot be felt; only a radiologist can tell from a mammogram.

The four density categories

Radiologists use the Breast Imaging Reporting and Data System (BI-RADS), developed by the American College of Radiology, to sort density into four categories. The names, as the US Food and Drug Administration (FDA) lists them, are: almost entirely fatty; scattered areas of fibroglandular density; heterogeneously dense, which may obscure small masses; and extremely dense, which lowers the sensitivity of mammography.33US Food and Drug Administration: Important Information: Final Rule to Amend the Mammography Quality Standards Act (MQSA) Lists the four density categories required in reports. They are often labeled A, B, C and D.

Categories C and D are the ones called dense. The NCI gives approximate shares of women in each group: about 10% almost entirely fatty, about 40% scattered, about 40% heterogeneously dense and about 10% extremely dense.11National Cancer Institute: Dense Breasts: Answers to Commonly Asked Questions Gives the approximate share of women in each category.

1. AAlmost entirely fatty
2. BScattered areas of fibroglandular density
3. CHeterogeneously dense
4. DExtremely dense

How common dense breasts are

Common. The NCI says nearly half of women aged 40 and older who get mammograms are found to have dense breast tissue.11National Cancer Institute: Dense Breasts: Answers to Commonly Asked Questions Nearly half of women 40 and older who have mammograms. The American Cancer Society puts it at about half of all women in the United States who have mammograms.22American Cancer Society: Breast Density and Your Mammogram Report Last revised September 2024; about half of US women who have mammograms. Cancer Research UK adds that younger women tend to have denser tissue than older women.44Cancer Research UK: Breast screening (mammography) Last reviewed May 2026; younger women have denser tissue.

Why density matters

There are two separate reasons. The first is masking. Dense tissue and many abnormal findings both appear white on a mammogram, while fatty tissue appears dark, so mammography is less sensitive in dense breasts and more likely to miss cancer. The NCI says people with dense breasts may also be called back for follow-up testing more often.11National Cancer Institute: Dense Breasts: Answers to Commonly Asked Questions Explains masking and more frequent callbacks.

The second is risk. The NCI states that dense breasts are a risk factor for breast cancer, separate from the effect on reading a mammogram, but that they are not considered an abnormal condition or a disease.11National Cancer Institute: Dense Breasts: Answers to Commonly Asked Questions Dense breasts are a risk factor but not a disease. The American Cancer Society says it is unclear why, and that most breast cancers can still be seen on a mammogram in dense breasts.22American Cancer Society: Breast Density and Your Mammogram Report Last revised September 2024; cause unclear; mammograms still advised. Other factors are covered under higher risk.

The US density notification rule

This section applies to the United States only. The FDA's amended mammography regulations, with enforcement beginning on September 10, 2024, require facilities to include an assessment of breast density in the report sent to the provider and a plain-language notice to the patient. The patient notice says the tissue is either dense or not dense; the dense version adds that other imaging tests in addition to a mammogram may help find cancers in some people, and urges talking to a healthcare provider.33US Food and Drug Administration: Important Information: Final Rule to Amend the Mammography Quality Standards Act (MQSA) Enforcement from September 10, 2024; quotes the patient notification statements. Elsewhere, practices differ.

Extra tests and what guidelines say

Supplemental screening means an extra test, usually ultrasound or MRI, on top of a mammogram. The NCI says that if you have dense breasts you may be offered MRI or ultrasound along with mammography, but it is not known whether this leads to better health outcomes.55National Cancer Institute: Screening for Breast Cancer Page dated August 2025; unknown whether supplemental MRI or ultrasound improves outcomes. The American Cancer Society says experts do not agree what other tests, if any, should be done, and that ultrasound and MRI can find some cancers a mammogram cannot but also produce more findings that are not cancer, leading to extra tests and biopsies.22American Cancer Society: Breast Density and Your Mammogram Report Last revised September 2024; experts disagree on extra tests.

The US Preventive Services Task Force, in its recommendation published on April 30, 2024, concluded that the current evidence is insufficient to assess the balance of benefits and harms of supplemental screening with breast ultrasonography or MRI in women identified to have dense breasts on an otherwise negative mammogram.66US Preventive Services Task Force: Breast Cancer Screening Final recommendation statement of April 30, 2024; an I statement on supplemental screening in dense breasts. That is a statement about missing evidence. An NCI summary describes a trial in which technologist-performed ultrasound after 3D mammography modestly improved cancer detection in dense breasts, by 1.3 cases per 1,000 in year 1, and also increased false-positive recalls.77National Cancer Institute: Breast Cancer Screening (PDQ) Summary for clinicians dated February 2026; describes the DBTUST trial. Newer approaches such as abbreviated MRI are still being studied for dense breasts.88American Cancer Society: Newer and Experimental Breast Imaging Tests Last revised July 2026; abbreviated MRI and contrast-enhanced mammography under study.

If you are also at higher risk because of family history or a gene change, different advice may apply; see the higher-risk page, and whether there is a better test than a mammogram.

What to ask your doctor

The NCI suggests asking whether you have dense breasts based on your most recent mammogram, whether additional screening is recommended for you along with its benefits and drawbacks, and what your personal risk of breast cancer is given your risk factors.11National Cancer Institute: Dense Breasts: Answers to Commonly Asked Questions Questions to consider asking your doctor or nurse. You might also ask what any extra test would cost. The main guide covers the basics of screening, and BI-RADS categories explains the result numbers on your report.