A hard lump in one breast is not normal and is associated with breast enlargement and hard lumps of mammary fibroids. Normal adult female breasts are hemispherical, slightly pendulous, with no hard lumps in the breast when touched by hand, and have a uniform and elastic texture. A hard lump when touching the breast is considered to be caused by breast disease. The hard lumps are classified as single or multiple, or both breasts may exist at the same time. Women with endocrine disorders caused by bad lifestyle habits, taking medications, and working late at night, which cause abnormal hyperplasia of the epithelial and mesenchymal structures of the breast. Before menstruation, due to changes in hormone levels, edema occurs between the lobules of the breast and hyperplasia occurs in the mammary glandular follicles. After the end of menstruation, hormone levels drop, pain gradually disappears, and mammary hyperplasia may also undergo pathological changes and form cysts around the breast ducts. If the lump is made larger and the pain is severe, it can be treated with medication. Breast lumps may also be caused by breast fibroids. Some women are sensitive to estrogen and will experience different degrees of hyperplasia in the breast area when stimulated by estrogen, and will find hard lumps inside when they touch their breasts with their hands.