Underarm chest side pain may be due to pleurisy, trauma, neuritis and other diseases. 1. Pleurisy: pleurisy is generally due to autoimmune diseases, infectious diseases or malignant tumors caused by the inflammation of the pleura, pleurisy will lead to pain on both sides of the chest under the armpit accompanied by symptoms such as chest tightness, and some serious patients will have difficulty breathing. 2. Trauma: If the patient has collision or extrusion, it may lead to soft tissue contusion or fracture at the axillary chest, which will trigger the symptoms of pain at the side of the axillary chest. 3. Neuritis: Chest neuritis can also lead to the symptoms of lateral chest pain, mainly due to intercostal neuritis, the pain caused by this disease is usually less sensitive. Underarm chest side pain may also be due to costochondritis, forks, etc. When this symptom occurs, it is necessary to consult a doctor for examination in time to avoid delaying the condition.