It is very common for the injection site to become red, swollen, and hard after the injection, which is an adverse reaction. Because the injection contains some adsorbents and other ingredients, it may have an irritating effect on the tissue, so the injection site may appear hard knots. In addition, there may be redness and swelling at the injection site. In this case, you can use hot towels to apply local heat to promote blood circulation and eliminate the hard knots. In addition, you can also use potato slices to apply external compresses on the hard parts, which also have a certain effect. If the injection site is still red and swollen, you can also use magnesium sulfate solution for external application, which can reduce the swelling. If the patient also has other clinical symptoms, it is necessary to go to the hospital for further examination and targeted treatment.