Red face after injection may be related to allergies, adverse drug reactions and other factors. 1. Allergy: if the human body is allergic to a certain component of the drug in the injection, when the injection, there may be histamine release and other immune reactions, resulting in redness of the face. 2. Adverse drug reactions: if the injection drug contains ingredients that can make capillaries dilate, but has nothing to do with the treatment of the relevant diseases, it may be due to the adverse reactions caused by the redness of the face. It is recommended to go to the regular hospital in a timely manner to clarify the cause of the red face after injection, if treatment is needed, should be standardized under the guidance of the doctor, so as not to delay the condition of the body to bring about adverse effects, and may even pose a threat to the life.