Allergy Myths 101: Iodine Allergy

There are many old wives tales or popular myths about how a person can treat their allergies. Here at Intermountain Allergy and Asthma, we have heard them all! As a way to help dispel allergy myths, we’ve invited Dr. Harris to share a few his thoughts in our “Allergy Myths 101” blog posts. 

Here is a popular allergy myth: There are cross-reactions between seafood and iodinated contrast (x-ray contrast dye) caused by “Iodine allergy”. 

What is Iodinated Contrast?

“Iodinated contrast is a form of intravenous radiocontrast (radiographic dye) containing iodine, which enhances the visibility of vascular structures and organs during radiographic procedures. Some pathologies, such as cancer, have particularly improved visibility with iodinated contrast” – Wikipedia.

It is true that some people have allergy-like reactions if they are given iodinated contrast dye during an x-ray procedure, and of course there are many people that have life-threatening allergic reactions after eating fish or shellfish.  However, the truth is that there is no connection between these two types of reactions and no ‘allergy’ relationship at all between seafood and radiologic contrast dyes.

I suspect that this allergy myth got started because radiology dyes and seawater/ seafood both contain iodine.

It isn’t clear why some people react when they are given iodinated contrast dyes, but we do know that it isn’t a true “allergy” to the dye (or to iodine) in the vast majority of cases.  It may be that the iodinated contrast dyes can affect the osmolality (the balance between water and electrolytes) in allergy cells and thus cause the cells to release their active contents.

During a true allergic reaction (such as with a fish or shrimp sensitivity), the immune system is involved and ‘allergic’ antibodies recognize a substance that we are sensitive to, and they (the antibodies) cause the release of active chemicals.  The immune system isn’t involved in most iodinated contrast dye reactions.  The reactions look the same, but take place for very different reasons.

What about people who have terrible reactions to seafood, and then get hives during an x-ray when iodinated contrast was used?

Those people do exist, but that is probably an example of someone who has two common problems at the same time – purely coincidental.  Someone who is allergic to fish is not at dramatically greater risk than anyone else to have a reaction during an x-ray procedure.  Someone who has a reaction to contrast dyes has about the same risk as everyone else to develop a seafood allergy.

Neither a reaction to contrast dyes nor a seafood allergy will cause any problems when consuming iodinated salt in food.

Duane J. Harris M.D.
Intermountain Allergy & Asthma of Draper

A Tip from Dr. Harris

By the way – We all need a little iodine in our diet for proper thyroid function.

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