Armpit tenderness may be related to upper extremity infections, axillary folliculitis, trauma and female breast diseases. 1. Upper extremity infection: there are a large number of lymph nodes in the armpit area, if the upper extremity infection occurs, the lymphatic system to remove bacteria from the infected area will cause axillary lymph node enlargement, and there will be obvious pain when pressed. 2. Folliculitis: there are a large number of hair follicles in the armpit, its location is hidden, excessive sweating can easily cause hair follicle blockage triggered by folliculitis, which will cause pain, redness and swelling of the armpit and other symptoms. 3. Female breast diseases: such as mastitis, breast tumors lead to abnormal proliferation of lymph nodes in the armpit will also cause pain in the armpit area, most of them are mainly swelling and pain. 4. Trauma: Shoulder and armpit soft tissue muscle strains caused by lifting heavy objects or car accidents can cause armpit pain, swelling, restricted movement, axillary pressure pain and numbness. There are many causes of axillary pain, it is recommended that patients go to the hospital for medical examination, complete the examination and follow the doctor’s instructions for treatment.