If there are no lumps but simply redness and pain, consider that it is caused by folliculitis. Due to the hot weather sweating more, armpit local skin permeability is poor, humid environment plus sweat stimulation leads to local skin redness, plus clothing and other friction may appear local breakage caused by pain. At this time, you can use povidone-iodine to disinfect, and then apply some anti-inflammatory drugs such as erythromycin ointment to control, and pay attention to skin hygiene, keep the local dry, reduce local friction. Female patients may also be caused by breast hyperplasia, the breast will have a caudal lobe extending to the armpit to appear breast hyperplasia, there will be pain in the armpit of the affected side. In addition, patients with neuritis or herpes zoster may also experience pain in this area.