The child’s back suddenly out of a small circle of small blisters do not itch, may be related to allergic dermatitis, mosquito bites, drug rash, shingles and other conditions. 1. Allergic dermatitis: if the child is allergic to the environment of animal hair, dust mites, pollen, intimate clothing materials and other substances, may lead to small blisters on the back area, in the early stages of the onset of the disease, there may be no pain and itching. 2. Mosquito bites: If the child’s back is bitten by mosquitoes, the mosquito body may contain venom, which may irritate the child’s skin, resulting in small blisters on the skin. 3. Drug rash: the child has recently been taking some kind of medication, may be due to drug factors, resulting in skin rash, may be accompanied by mild itching symptoms, but the child does not notice. 4. Herpes zoster: This is caused by infection with the varicella zoster virus, and is mainly manifested as a series of blisters on the back against the waist. The sudden appearance of small blisters on the back of the child painless and itchy may also be caused by other reasons, it is recommended that parents take their children to the doctor in a timely manner, to do a systematic examination, to clarify the cause of the disease in the doctor’s guidance to treat the symptoms.