What does shellfish have to do with your feet?

Shellfish contains iodine. While iodine occurs naturally and rarely causes allergic reaction, in severe allergies it is believed that there may be a link in allergy to shellfish and iodine itself. Iodine is used in podiatry as an antiseptic. In some instances it is used as a recommended topical for use on open wounds, but it is also used on the skin to prep certain areas for injections as a precaution to prevent infection.