Hard lumps in breasts during breastfeeding are usually caused by breast milk stagnation, breast hyperplasia and breast tumors. 1. Breast milk stagnation: the most common during breastfeeding is breast milk stagnation, when there is breast milk stagnation, we must gently massage the stagnant milk out. After breastfeeding, if the milk is not empty, use a breast pump to empty the milk, which can reduce the patient’s symptoms. 2. Breast hyperplasia: when the body under the action of estrogen, breast hyperplasia will occur, manifested as localized nodules in the breast, mostly accompanied by pain, at this time, it is feasible to diagnose by breast ultrasound, and regular rechecking can be done. 3. Breast tumors: benign tumors mostly, such as benign tumors in the breast before pregnancy, with the changes in hormone levels during pregnancy, the lumps that were not found before pregnancy, will suddenly increase in size. The causes of breast lumps during breastfeeding also include mastitis, malignant tumors and other causes, and it is recommended that patients go to the breast surgery department of the hospital in time for examination.