Sudden enlargement of the breasts may be due to the following reasons:1. It may be caused by the sudden aggravation of breast hyperplasia, and the enlarged breasts may be accompanied by swelling and pain, which will be obviously aggravated before the onset of menstruation, and relieved after the onset of menstruation, and the patient can go to the hospital for ultrasonography for a clear diagnosis.2. Inflammatory diseases of the breasts including non-lactating mastitis, breastfeeding mastitis, most of the skin will be obviously red and swollen, and the patient accompanied by fever and other general symptoms.3. Mastitis, most of the skin will have obvious redness and swelling, the patient accompanied by fever and other systemic symptoms. 3, occupational lesions, breast cystic occupations may suddenly increase in size, need to go to the hospital for ultrasound examination. The lesions can be aspirated for fluid, but they are all benign, so patients don’t have to be nervous.4. It is possible that the effects of pregnancy, the most common reaction of the human body when pregnant is the enlargement of the breasts as well as the swelling and pain and discomfort.5. The reaction will be seen after the regular sexual intercourse.