Everyone’s breasts are different. Some women have naturally lumpy—or fibrous—breasts. Others have water-filled cysts that may shrink or expand depending on time of month. Neither is dangerous. If you feel the same lumpiness in both breasts, it’s probably just fibrocystic—but healthy—breast tissue, says William Owens, M.D., director of the Aurora BayCare Medical Center Comprehensive Breast Care Center in Green Bay, WI. “If, however, the woman feels a lump on one side and does not feel a similar lump in the mirror image of the other breast, this should be investigated.” If you notice a lump, call your doctor. Lumps in the breast could be a sign of infection, injury, or cancer.