A hard and painful lump on the inner thigh is caused by a soft tissue infection. The typical symptoms of a subcutaneous soft tissue infection are local redness, swelling, heat and pain. Redness is redness of the skin surface; swelling is the appearance of soft tissue swelling and hard lumps; heat is an increase in surface skin temperature, and possibly even an increase in body temperature; pain is pain. Mainly Staphylococcus aureus infection is dominant. Therefore, treatment should start with oral antibiotics, such as cefixime or cefradine, and also intravenous penicillin or a generation of cephalosporins, such as cefothiamidine. If there is localized suppuration, abscess and fluctuating formation during the treatment, the abscess needs to be cut open under local anesthesia to drain the pus, and then wound dressing is performed. In this way, the extent of redness and swelling can be gradually reduced and the condition can gradually improve.