Up to half of all women have dense breast tissue, which is a risk factor for breast cancer.
Dense breast tissue is also more difficult for doctors to see through on mammograms. That means it's more difficult for them to find cancerous tumors within that breast tissue.
As of January 1, doctors and hospitals in North Carolina are required to tell a woman after a mammogram that she has dense breast tissue and that she may want to talk with her doctor about additional screening tests.
There is now a bill in the South Carolina Senate that would create a similar law.
For much more on dense breast tissue and the push to make women aware of it, click on the video box above to watch my special report.