What causes dense breast tissue?

It's not clear why some women have a lot of dense breast tissue and others do not.

You may be more likely to have dense breasts if you:

• Are younger. Your breast tissue tends to become less dense as you age, though some women may have dense breast tissue at any age.
• Have a lower body mass index. Women with less body fat are more likely to have more dense breast tissue compared with women who are obese.
• Take hormone therapy for menopause. Women who take combination hormone therapy to relieve signs and symptoms of menopause are more likely to have dense breasts.