The redness and swelling of the arm after the diphtheria vaccination must be determined by the cause of the redness and swelling to determine how long it will take to heal. If the redness and swelling is caused by local soft tissue irritation due to the vaccine inside the diphtheria, the redness and swelling will subside on its own in about 1-2 days, as the vaccine is metabolized through tissue absorption in about 1-2 days, so it will subside soon. However, if bacterial infection occurs at the mouth of the injection, resulting in redness, pain and even pus, the time required to get well after regular treatment must be about a week before the inflammation is completely controlled and the redness and swelling of the skin can subside.