Hidden pain under the left breast may be caused by costochondritis, mastitis, trauma, angina and other factors. 1. costochondritis: this disease may be due to trauma, chronic strain and other factors, the patient may have symptoms of pain under the left breast. 2. Mastitis: the disease may be related to milk stagnation, infection and other factors, due to inflammation stimulation of the tissues under the left breast, pain may occur. 3. Trauma: Trauma to the lower part of the left breast, such as impact or sharp instrumental injury, can also lead to symptoms of hidden pain. 4. Angina pectoris: angina pectoris can be induced by ischemia and hypoxia of the heart muscle cells, and the patient may experience vague pain under the left breast. In addition, breast cancer, breast hyperplasia, breast fibroma, herpes zoster and other diseases may also appear similar symptoms, caused by a number of factors under the left breast hidden pain, it is recommended to consult a doctor in time to identify the cause of the disease.