Growing fat with sudden breast fullness usually does not cause swelling and pain. When you grow fat, the fat content in your body gradually increases, and so does your weight. The chest fat content in the breast area is also increasing, so the chest will appear suddenly plump. Gaining weight is simply an increase in fat content, which does not lead to a feeling of swelling and pain in the breasts, and the breasts generally do not show any discomfort such as significant swelling and pain. The swelling and pain in the chest may be related to other reasons, such as before menstruation, there may be swelling and pain sensitivity phenomenon; if the swelling and pain is accompanied by breast lumps, nipple overflow, consider that it may be mammary hyperplasia; if there is a tingling in the breasts, fever, etc., it may be mastitis; if there is cellulite changes in the skin, nipple overflow and so on, it may be breast cancer, and so on. It is recommended that the patient consult a doctor in a timely manner to clarify the cause of the disease and actively cooperate with the doctor for treatment if necessary.