There is no such thing as underarm pain in men to be on the lookout for four diseases. It may be caused by excessive pulling, or it may be caused by folliculitis, chest wall tumor and other diseases. 1. Excessive stretching: If men have often performed upper limb activities recently, but because of improper activities, resulting in excessive stretching, causing tendon injury, it is easy to cause underarm pain. 2. Folliculitis: there are more hair follicles in the armpits, which are susceptible to pathogenic bacterial infections, such as Staphylococcus aureus, leading to the induction of folliculitis, which is mainly manifested by the presence of localized red papules, and pus may appear in the later stage, accompanied by obvious pain. 3. Metastasis of malignant tumors: malignant tumors in other parts of the body, such as lung cancer, stomach cancer, bone cancer, etc., can be metastasized to armpit through lymph and blood transport, which can be manifested as underarm pain. There are many reasons leading to men’s underarm pain, and it is necessary to go to the hospital to improve the examination in order to clarify the specific reasons.