What can cause blue veins on your breasts?

Common: Sometimes they seem to appear after breast surgery, such as augmentation. However, they are not uncommon even in someone who has not had this procedure. These are really just normal veins, perhaps more visible because they are close to the surface of the skin and possibly because they might enlarge over time. In my experience, they often respond well to gentle sclerotherapy.

Breast veins: Breast veins may become enlarged with puberty, pregnancy, oral contraceptives or breast augmentation. This will not harm your health.