Hardness in the arm after DPT vaccination is usually a normal local reaction. DPT vaccine is used to prevent whooping cough, diphtheria and tetanus, after vaccination, local redness, swelling, pain, itching and local hard nodules may appear at the injection site, which can be absorbed in 1~2 months. At this time, it is necessary to pay attention to the nodule to avoid extrusion and water, and after 48 hours, it can be appropriate to apply hot compresses, which can promote blood circulation, promote absorption, and reduce redness, swelling and nodules. However, severe cases can be accompanied by lymphadenitis or lymphadenitis, lymphadenitis is manifested as one or more red lines appearing near the wound, localized hardness and swelling and pressure pain, which can be accompanied by fever, fatigue and other systemic symptoms; lymphadenitis and the main clinical manifestations of lymph nodes are enlarged and painful; at this time, we need to consult a doctor in time. In summary, the inoculation site has a mild redness, itching or low fever, generally do not need special treatment, that is, subside on their own, if there is a serious reaction to timely treatment.