The standard of care for surgical skin preps is the use of povidone-iodine. We use this substance on a daily basis and it is safe around and on the eye. But what happens in the rare instance that a patient tells us that they are allergic?
Iodine is a trace element present throughout the body and is essential for the production of thyroid hormones. It is not possible to have a true allergy to elemental iodine. When people refer to an “iodine allergy,” it usually means an allergy to iodinated radiological contrast media or topical povidone-iodine.
The newer iodinated contrast medias have improved chemical properties so the incidence of allergic reactions is much lower. As far as topical povidone-iodine allergies, they present like a contact dermatitis with redness, induration with or without small blisters. The rare systemic reaction to povidone-iodine antiseptics are extremely rare and are thought to be due to povidone rather than iodine. One can present with a skin reaction resembling a chemical burn following prolonged skin contact with povidone-iodine saturated drapes during surgery, thought to be due to the direct toxic effects of povidone-iodine.
The question of cross-reactivity is often raised: if someone has an iodinated contrast media allergy, will they have a topical povidone-iodine allergy? Cross-reactivity between povidone-iodine and iodinated contrast media has not been demonstrated, as topical allergies are thought to be caused by povidone. A contact allergy to povidone-iodine antiseptics does not preclude the use of iodinated contrast media, but the risk of reaction may be slightly increased.
Another misconception is that if one has a shellfish allergy, they will be at risk for having an adverse reaction to iodine. Research has shown that shellfish allergies are not linked to iodine allergy. Proteins such as parvalbumins and tropomyosins in fish are responsible for seafood allergies.
So the next time a patient presents with a history of a topical iodine allergy, consider patch testing them. Realize that because they have a shellfish allergy or an IV contrast allergy to iodine doesn’t mean they will react negatively to topical povidone-iodine.