Redness and swelling of the arm after vaccination may be a normal reaction to vaccination, which can be relieved by applying cold compresses and then hot compresses as appropriate. May also be a local infection, if the arm redness and swelling is more serious, we should let the professional doctor for examination and treatment, such as local disinfection, anti-infection treatment or incision and drainage. 1. Adverse reactions to vaccines: appropriate cold compresses and then hot compresses: for children with red and swollen arms after vaccination, you can appropriate cold compresses to relieve the symptoms of local congestion, and then hot compresses to promote swelling. 2. Local infection of the vaccination site: you can use iodophor to carry out local disinfection under the guidance of professional doctors, and then apply anti-infection ointment, such as mupirocin ointment. If serious purulent infection occurs, we should cooperate with the doctor to take surgical incision and drainage as soon as possible. Therefore, redness and swelling of the arm after vaccination is relatively common in children, but it is also necessary to pay attention to it and observe whether the redness and swelling are serious. If the redness and swelling of children’s arms after vaccination is more serious, it is recommended to go to a regular hospital as soon as possible, so that the professional doctor to deal with.