Hard lumps on the arms of babies after hepatitis B vaccination can usually be absorbed on their own and do not require special treatment. However, if the hard lumps are large and accompanied by other symptoms, they should consult a doctor in time and be treated accordingly. Hepatitis B vaccine belongs to inactivated vaccine, which is a special medicine used to prevent hepatitis B. After receiving hepatitis B vaccine, it can stimulate the body’s immune system to produce corresponding antibodies, which will work when infected with hepatitis B virus, thus eliminating the virus. Most people do not experience adverse reactions after receiving the hepatitis B vaccine. Hard lumps at the vaccination site on the arm of a baby after hepatitis B vaccination can usually be absorbed on their own and do not require special treatment. However, if the hard lumps are large in size and localized inflammatory reactions such as redness, swelling, heat and pain are present, hot compresses using hot towels can be applied to promote the dissipation of their inflammation and facilitate absorption and healing. After the baby received the hepatitis B vaccine, should pay attention to rest, and keep the vaccination site clean, avoid getting wet, so as not to cause infection, such as the emergence of obvious symptoms, should go to the hospital in time for further diagnosis and treatment.