The causes of blisters in armpits are considered to be herpes zoster, eczema, prickly heat and so on. 1. Herpes zoster: when the body is infected with varicella-herpes virus, it will cause blisters to appear locally on the skin, and the blisters may grow in the armpits, at this time, you should apply acyclovir cream or take acyclovir tablets orally to carry out antiviral treatment on the blisters. 2. Eczema: the skin of the armpit is thin, the possibility of eczema is high, then there will be armpit blisters, routine blood test eosinophils will be elevated, the treatment of antihistamines such as fexofenadine hydrochloride tablets and so on. You can also apply glycerin lotion locally. 3. Prickly heat: Repeated friction of the armpit skin and accumulation of sweat in the local area can also lead to the above situation, which can be treated by applying topical glycerine lotion to keep the area dry. It is recommended to consult a doctor for a clear diagnosis.