Breast swelling and pain may be related to physiological reasons, spontaneous pneumothorax, breast diseases and so on. 1. Physiological reasons: When a woman is in puberty or physiological period, the level of estrogen in her body will increase, resulting in breast congestion and edema as well as expansion of the milk ducts, which will lead to swelling and pain in the breasts. Usually, breast swelling and pain occurs before menstruation and disappears on its own after menstruation is over. 2. Spontaneous pneumothorax: most of them are acute in onset, easily triggered by intense sports, lifting heavy objects, etc., and manifested as chest tightness, chest pain, dyspnea and other symptoms. 3. Breast diseases: such as breast hyperplasia, which can lead to hyperplasia-like changes in the glands and alveoli in the breasts, resulting in bilateral breast distension, pinching pain, etc. Usually after menstruation, the pain can be relieved on its own. If breastfeeding women experience breast swelling and pain, it is important to consider the possibility of acute mastitis caused by accumulation of breast milk. Chest pain can also be seen in other diseases, patients are advised to seek timely medical treatment, so as to avoid delaying the condition.