A four-month-old child with a red rash all over his body after a vaccination shot may have a drug rash. The self-healing time of the disease is related to the severity of the disease, physical fitness and other factors, and cannot be generalized. Rash all over the body after vaccination, may be drug allergic reaction, mainly manifested as a rash, itching, severe cases may lead to anaphylaxis. If the rash is simple, the rash is small, the child’s physical condition is good, not accompanied by other uncomfortable symptoms, about two or three days may be relieved on their own. Some children with poor physical condition, severe allergic symptoms or anaphylactic shock after vaccination, it is recommended to go to the hospital in a timely manner, combined with the doctor’s advice, the administration of anti-allergy drugs, such as loratadine syrup, can promote recovery. In summary, drug allergy caused by different symptoms, different physical quality of the child, different clinical manifestations, the disease recovery time is also different. If the symptoms are serious, it is recommended to go to the pediatric department of the hospital, combined with the doctor’s advice treatment, to avoid affecting the health of the body.