Most of the localized hard lump reaction after DPT injection is a normal phenomenon. Generally speaking, the injection of DPT into the local skin of the body leads to an antigen-antibody immune response to the DPT vaccine in the local skin. In the process of this immune reaction, clinically speaking, it is an antigen-antibody reaction; in common parlance, it is a localized positive and negative combat reaction. In the course of the reaction, some tissue or other damage will occur, resulting in the formation of localized nodules, redness and swelling. After the formation of redness, swelling and hard nodules, the main prevention of local bacterial infection can be, to avoid water loss, close observation. If there is obvious local redness, swelling, whitening, pus, these need to go to the hospital in time to deal with.