The redness and swelling of the baby’s arm after vaccination can be treated with hot compresses, and if there is persistent swelling, it is necessary to consult a doctor in time. The redness and swelling of the baby’s arm after vaccination is mainly caused by the adverse reaction of the vaccine. Some of the components of the vaccine can cause local skin reactions, and redness and swelling. You can use a hot towel to apply warm compresses to promote blood circulation, then the redness and swelling can gradually disappear. But if the effect is not obvious, or even aggravated, then we need to consult a doctor. Infection at the inoculation site cannot be ruled out, which may cause the redness and swelling to continue to swell, or even pus. It is necessary to carry out blood tests and other tests in a timely manner to clarify the type of infection and then take anti-infection treatment.