Painful underarm sores may be caused by secondary infection of axillary sebaceous cysts and axillary folliculitis, which need to be treated with medication and surgery in a timely manner. 1. axillary sebaceous cysts secondary infection: axillary distribution of sweat glands, if you do not pay attention to hygiene caused by sebaceous cysts, and secondary infection, the local redness, swelling, pain, pus, the need for timely surgical treatment, the cysts will be removed, and oral penicillin, erythromycin and other medications for anti-infection treatment. 2. Axillary folliculitis: when the axillary hair follicles are infected by pathogenic bacteria, red papules will appear at the mouth of the hair follicles, accompanied by redness, swelling and pain, and in severe cases, pus may turn into pus and ulcerate, and surgical treatment is also required to drain the pus, and locally apply mupirocin ointment, fusidic acid cream, etc., or take antibiotics orally. The use of medications should be under the guidance of a medical professional.