The myth of iodine allergy

The Pediatric Insider

© 2013 Roy Benaroch, MD


Since every second of my life, and then some, seems preoccupied with the transition to the New and Improved ICD-10 code set — I can’t imagine how I lived so long without being able to code for macaw attacks – I’ve had no time to write anything new. So today you get a refurbished, classic post. And by classic, I mean old. I put a new photo somewhere in the text to freshen it up, so I promise it’s worth a read. Enjoy!


One of the goals of this site—along with soliciting donations and letting me write and publish goofy stuff—is to promote good, solid science-based medical information. If you’ve been around, you know I don’t go for made-up-stuff. And I especially don’t like it when it’s other doctors spreading the misinformation.

Have you had a reaction to intravenous contrast dye during a CT scan or other exam? Have you been told you’re allergic to iodine, and that you should avoid seafood?

Wrong wrong wrong. You’re not allergic to iodine. And you can almost certainly have seafood—you’re no more likely than anyone else with any allergy to be allergic to seafood, or salt, or dairy products, or anything else that contains natural or added iodine. The only thing you may need to avoid is that same kind of IV contrast dye in the future—though even then, it can probably be safely used with simple premedication.

Iodine is a natural element. It is essential for life—if you didn’t have any, your thyroid gland couldn’t work, and you’d get sick and die. Iodine is found especially in seafood, but also in some vegetables and dairy products (especially if the cows were grazing on land where the soil was rich in iodine.) In many countries, including the USA, salt is routinely fortified with iodine to prevent thyroid disease.

Allergies are almost always triggered by proteins—big, honking, complex molecules made of chains of amino acids—or other big molecules. Someone who’s had a reaction to IV contrast dye has not reacted to the iodine, but to the other constituents of the dye. People who’ve had these reactions may need to be premedicated or use a different, low-reaction type of dye is used in the future if they need further studies.

These are dangerous macawsIt may be that people who’ve had reactions to IV contrast might also have a food allergy, and that food allergy might even be to seafood. But there is no increased risk of seafood allergy than to allergy to any other foods. You might be allergic to seafood or milk or eggs or peanut or… nothing. But you’re not allergic to iodine.


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3 Comments on “The myth of iodine allergy”

  1. wzrd1 Says:

    Would that someone explain that to my wife’s body. She suffers from edema on contact with shellfish or iodized salt. Extremely low doses seem to be tolerated, as iodine is nearly ubiquitous in foods.
    I suspect it’s the form presented in iodine containing compounds, where the lower dosage is bound more tightly inside of protein complexes, compared to other forms such as in shellfish or whatever form it’s in in iodized salt (potassium iodide, perhaps?).
    It’s likely that her immune system reacts to a rather simple molecule, rather than the honking great complexes found in many proteins.
    But then, to add to the joy of finding a diagnosis with her, she also suffers from Lupus, suggesting an already hypervigilant immune system.

    My wife also has the darnedest sensitivity to capciscum, with blistering on contact with even a chilli pepper, anything ‘hotter’ and the blistering is more severe. It’s unrelated to iodine, but hang all if I’ve saw such a reaction in others.
    Any notion on that reaction?


  2. Dr. Roy Says:

    Wzrd, contact edema from shellfish is easy enough to explain through ordinary IgE mediated allergy — the same phenomenon that’s used to do scratch testing at an allergist’s office.

    Capsicum reaction could be allergic or related to chemical irritation. Capsicum itself is there to cause reactions in animals who might eat the plant at the wrong time (though we’ve bred hot peppers to have far more capsicum and related compounds than occur in nature.)

    Lupus itself is associated with all kinds of skin reactions, including idiopathic urticaria (ie unexplained hives).

    I don’t think iodine or salt itself could be triggers specifically. Perhaps some other anti caking agent or something in the salt. Does kosher salt cause a reaction? I think that’s just NaCl with nothing added.

    Iodine in salt is added as potassium iodine or potassium iodide — both are just potassium and iodine, and neither itself really should trigger any kind of reaction. Your body is full of both K+ and I- ions already. Though actually base Iodide (I2) is corrosive, I don’t think it’s present in salt.


  3. wzrd1 Says:

    Her reaction to both looks to be something an immunologist needs to review, this is far beyond my level of expertise. It’s certainly not something we could address over the internet, unless someone has a Star Trek tricorder in their pocket to loan us. 😉

    I suspect the OC sensitivity is just an overreaction, it is an irritant, her body doesn’t seem to handle that particular irritant well.

    No reactions with kosher salt, oddly sea salt doesn’t cause a reaction and I’m quite certain iodine is present in it. Just a lower level.

    Iodine is indeed corrosive, although small amounts can be used for water purification. I suspect the iodine in salt is KI, it’s quite common and is also in nuclear response preventative stockpiles should radioiodine be released from a nuclear reaction.
    It’s a head scratcher, sounds like something a new primary will have to review when we finish our relocation and our health insurance kicks in.

    At least her Lupus thus far has only been striking connective tissue. Her maternal aunts and cousins ended up with cardiac tamponade, secondary to fluid accumulation in the pericardium. It was initially thought to be idiopathic until one cousin had repeated episodes and the appropriate markers were detected in her blood. Word passed around, family members spoke with doctors and a wave of positive tests resulted in effective treatment.
    Amazing what can happen when doctor and patient operate as a team. 🙂


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