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.
