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Fact Sheet: Breast Density Seen on Mammograms

What is breast density?

Women's breasts are made up of two kinds of tissue:

  1. Fatty tissue, which is made up of fat
  2. Glandular tissue, which is made up of ducts, glands for producing milk and supportive tissue

A breast is considered "dense" when it has a lot of glandular tissue, which looks white on a mammogram (the fatty tissue looks grey or black). The amount of density a breast has cannot be felt by a physical examination.

Who is likely to have dense breasts?

Generally, younger women have denser breasts than older women. This is normal because younger women have higher levels of the female hormone estrogen. As women grow older, their breasts often become more fatty and less dense.

Why is breast density important?

Women with high breast density are thought to have an increased risk of developing breast cancer. In addition, very dense breast tissue may sometimes make detecting breast cancer difficuIt on a mammogram.

What happens to women with dense breasts in the Ontario Breast Screening Program (OBSP)?

If your mammogram shows that your breasts have 75% or more dense tissue, the radiologist will recommend that you return in one year's time for a mammogram.

If your breast density decreases, your screening interval will return to every two years.

Is there anything I can do to change my breast density?

Breast density often decreases with age.

In some women, taking hormone replacement therapy (HRT) for menopause can increase their breast density.

We recommend that you discuss your options with your family doctor or nurse practitioner before making any changes to your medication.

About the Ontario Breast Screening Program (OBSP)

To learn more, visit or contact us at or 1.866.662.9233 from Monday to Friday, 8:30 a.m. to 5:00 p.m.

Need this information in an accessible format?
1.877.280.8538 / TTY 1.800.855.0511 |