If you are looking for a hard bump on the side of the foot, it may be caused by the following two conditions: 1. the formation of corns, the inside side of the foot and shoes are often subject to friction, the skin surface of the keratin layer is often stimulated and lead to sterile inflammation, over time there will be the formation of local hard nodes, pressure on the local will be more painful. 2. superficial swellings, common sebaceous cysts, fibroids, lipomas, etc.. These are benign swellings and will not be painful if there is no local infection or inflammation, and can be identified by local ultrasound. If it is distinguished from corns, it is usually based on the criterion of whether there is pain on pressure.