Reasons for lumps in breast during breastfeeding: First, because of excessive milk secretion in the body, the excess milk is not able to be discharged in time, forming a blockage in the body, which will form a hard lump after a long time. Secondly, it may be that there is a bad cell proliferation inside the breast, and the proliferated cells will cause the ducts of the breast to be blocked, and the lumps will be caused by the continuous accumulation of cells. Third, if the body’s hormone secretion is not good, estrogen constantly gathered will also stimulate the internal breast, the accumulation of soft tissue appear breast lumps.