Dense breast tissue is made up of thick fibrous tissue and milk glands. It’s different from fatty breast tissue, but both kinds of tissue are normal. You can learn how dense your breasts are from your mammogram report.

Dense breast tissue can make cancer harder to see on a mammogram. That’s because dense tissue looks white onscreen, just like cancer does.

Things that can affect breast density include family history (genetics), being pregnant, and using estrogen hormone therapy. Age can also make a difference—breast tissue in younger women tends to be denser than in older women who have been through menopause.