The underarms are always red, swollen and painful in summer, which may be caused by poor personal hygiene, folliculitis and eczema. 1. Poor personal hygiene: If the patient’s personal hygiene is poor, the underarm area is prone to itching symptoms, if the patient scratches the area, the underarm area will scratch red, excessive force, will lead to bleeding in the underarm area, which in turn causes pain. 2. Folliculitis: this disease is mainly due to bacteria, fungi and other pathogens caused by hair follicle infections, so that the patient’s underarms are always red, swollen and painful in the summer, and serious pus, ulceration and so on. 3. Eczema: armpits are always red, swollen and painful in the summer, may be due to eczema, is caused by a variety of internal and external factors caused by the superficial dermis and epidermal inflammation caused by and accompanied by self-conscious itching, scratching will aggravate the symptoms. If the symptoms are more serious, it is recommended that patients go to the hospital, under the diagnosis of the doctor, according to the condition, to take targeted treatment, life should pay attention to personal hygiene, avoid touching irritating objects.