A hard lump in the breast during breastfeeding is not painful and can be caused by breast milk stagnation, breast cysts, fibroid lesions and so on. 1. Breast milk stagnation: Breast milk stagnation, excessive breast milk, unsmooth discharge of breast milk and other reasons can cause breast milk stagnation into lumps. This can lead to hard lumps in the breasts during breastfeeding without pain. At this time, it is recommended to use a breast pump to suck out the milk from the breasts. At the same time, you can use a warm towel or gentle massage to relieve the hard lumps. 2. Breast cysts: benign lesions. Due to the relatively high level of estrogen secretion in breastfeeding women, if there are cystic changes in the breast, it can stimulate the cyst to become hard. 3. Fibroid lesions: there is a certain relationship with the level of estrogen secretion. When fibromatosis occurs in the breast, it can lead to the appearance of rounded and easy to push hard lumps in the breast, which have obvious boundaries with the surrounding tissues, and most of the patients do not have pain symptoms. At the same time, the presence of hard lumps in the breast will also exist the possibility of breast malignant tumors, breastfeeding chest with a pile of hard lumps and no pain, you should be vigilant, it is recommended to regular hospitals for breast surgery, through the specialist physician to carry out physical examination and other auxiliary examination, a clear diagnosis, targeted treatment.