Painful hard lumps in the breast are associated with cystic hyperplasia, acute mastitis, and intraductal papilloma of the breast. When there is a hard lump in the breast with painful manifestations, it is considered to be caused by breast enlargement. Mammary gland hyperplasia does not cause pain, but increased hormone levels in the body before menstruation and edema of the lobules and alveoli of the breast with hyperplasia cause pain at the site of the lump. It is also considered to be caused by acute mastitis, a disease that tends to occur in breastfeeding women due to acute purulent infection of the breast tissue, which can be accompanied by increased skin temperature and fluctuating pain in the early stages. Most patients with intraductal papilloma do not have obvious clinical manifestations, but sometimes the nipple area may cause local pain due to inflammatory stimulation.