A little bit behind the arch of the foot has a bulge, considering that the bulge is caused by infection, tumor, osteophytes and related skin lesions, etc., which need to be combined with specific symptoms and related auxiliary examination to clarify the cause. 1. Infection: the skin in the bulge area is often broken, and in the case of improper disinfection treatment, it leads to bacterial invasion, which causes local soft tissue oozing and edema, and most of them can be accompanied by pain, and even abscess can be formed, which is in the shape of a bulge. 2. Tumor: it is mostly seen in local tendon sheath cysts, which is related to local strain and trauma; it may be lipoma, which is related to improper diet and life habits; it may be fibroma, which is related to endocrine disorders and other factors in the body. 3. Osteomalacia: belongs to degenerative changes, which is caused by strain, trauma and long-term ligament pulling in the affected area, and belongs to bony protrusion. 4. Local skin lesions: mostly caused by friction and extrusion of the local skin, such as callus, etc., may also be due to warts caused by human papilloma virus infection. If the arch of the foot behind a little bit of bulge if accompanied by obvious discomfort symptoms, it is recommended to timely to the hospital, improve the relevant examination, clear cause of the disease, and then comply with the doctor’s instructions for targeted treatment.