Blisters on the back of the feet, many of which are symptoms of friction blisters, insect bite dermatitis or aspergillosis. 1. Friction blisters: the skin on the back of the foot rubs against shoes and other contacts for a long time, and the shear force produced by repeated skin friction separates the cuticle from the skin, and the gap after separation is filled with tissue fluid to form blisters. 2. insect bite dermatitis: mosquito bites insect venom stimulate local skin, easy to form pimples, blisters and other rashes, the typical rash is in the center of the skin pimples appeared pinpoint size blisters, accompanied by obvious itching. 3. Pemphigus: the cause is unknown, mainly caused by the immune system to attack its own epidermis, and genetic, drug and other factors, preferably in the middle-aged and elderly. Blisters on the back of the feet may also be other reasons, it is recommended to consult a doctor in time to clarify the diagnosis.