Itching and pain under the armpit mainly have the following points: 1. Consider eczema dermatitis. Severe eczema dermatitis will appear local itching, dry crack will appear painful and appear oozing. In this case, you can apply petroleum jelly externally to moisturize, avoid hot water, use alkaline soap handful of washing. The first thing you need to do is to go to the hospital to do a fungal immunofluorescence test, and after the diagnosis, antifungal treatment will be possible. 3. Herpes zoster. Viral infection can lead to herpes zoster, the rash appears erythematous, blisters with pain, and itching when dry crust. This condition can be treated with antiviral and nerve nourishing treatment.