Cysts are fluid-filled masses under the skin. Common cysts of the feet include synovial cysts, ganglia, and cutaneous mucoid cysts.

Most foot cysts are located under the skin, although occasionally they appear in tendon or bone. Synovial or ganglionic cysts are connected to a nearby joint or tendon, which makes them harder to treat. Mucoid cysts are not connected to a joint. Most cysts lead to mild pain as a result of the pressure created by wearing shoes. When any of these cysts enclose or press on a nerve, they can cause a sharp pain. X-rays, ultrasound, MRI, or CT scans are common methods for diagnosing cysts in the feet.

The best way to prevent cysts from forming is to wear well-fitted, comfortable shoes and avoid repeated foot injuries. Persistent ganglion cysts can be treated by numbing the area and extracting the fluid inside. A steroid or hardening agent may then be injected into the cyst to try to prevent it from filling again.