The bulge on the arm hurts when pressed, this may be an infection of the subcutaneous soft tissue. Due to certain infections in the subcutaneous soft tissues, some inflammatory reactions may occur, and these inflammatory reactions are usually characterized by edema, swelling, and congestion along with high skin temperature and tenderness. In addition, there may be swelling of the surrounding lymph nodes. For these infections, the first need to carry out antibiotic treatment, the general local can use Jin Huang San external application, or use ichthyol cream external application, at the same time you can take some oral antibiotics, generally can be oral roxithromycin or cefixime, cefadroxil and so on.