Today, allergies are more common than ever before. Food, pollen, and animal allergies are on the rise in both children and adults. It’s relatively easy for most people to reduce exposure to irritating agents, none of which are really required for survival. But, our bodies do require iodine…so how could anyone have an allergy to a nutrient required by the human body? Is it actually possible for the human body to be allergic to an element necessary for maintaining life?
The answer: not quite. The idea that someone could be allergic to naturally-occurring iodine arose from the misconception that those who were allergic to shellfish were allergic to its iodine content.  Shellfish allergies occur as a reaction to the proteins present in the food and not as a result of the iodine. However, studies have found that sensitivity to iodine-based contrast dyes, often used in medical imaging, can be an issue for some people.
Allergy to Iodine-Based Contrast Dyes
To the untrained eye, the typical x-ray image means absolutely nothing. And even to the trained eye, it doesn’t always show everything. Iodine-based contrast dyes are used to improve the quality of images produced from x-rays or computed tomography (CT) scans. Reactions to these dyes occur not from the iodine itself, but rather from the molecules within the contrast dyes.  Although exposure to these dyes can prompt typical allergy symptoms, they do not appear to trigger an allergic response in the generally-accepted sense.
People who do suffer from an allergic reaction to these types of dyes typically experience mild reactions such as nausea, vomiting, itching, and flushing. Serious anaphylactic responses can occur in a minor subset of individuals, including difficulty breathing, low blood pressure, cardiac arrest, and sometimes death. 
After an initial response from contrast dyes, individuals may also experience topical reactions to iodine-based solutions. One case of a man suffering from an iodine allergy developed a skin reaction following exposure to iodinated radiographic contrast media. Povidone-iodine and potassium-iodide solutions also show similar skin effects.   The reasons behind topical reactions continue to be studied.
Statistically speaking, persons with asthma and cardiomyopathy seem to have an increased chance of suffering from an allergy to iodine-based contrast dyes. The degree of severity of this allergy has been linked to age, sex (females are more likely to be affected), and the use of ACE inhibitors and beta blockers. 
Why You Shouldn’t Avoid Iodine
People with allergies to any type of fish need to be wary of the myth that it’s because of the iodine. It’s just not true; allergies to dietary iodine are extremely uncommon. The allergic reaction to iodine-based dyes, however, is something that needs to be further studied.
Remember this, your body needs iodine every day for proper thyroid function. It’s essential for your metabolism and energy levels. If you suspect you have an iodine deficiency, it may be wise to start supplementing with a nascent iodine supplement. Unless you’re eating a lot of seaweed (and then you may have to be careful about it being sourced near Fukushima), it can be challenging to get enough iodine through food.
Everything You Need to Know About Iodine
- Huang, Shih-Wen. Seafood and Iodine: An Analysis of a Medical Myth. Allergy and Asthma Proceedings, Volume 26, Number 6, November-December 2005, pp. 468-469(2).
- Scherer K, Harr T, Bach S, Bircher AJ. The role of iodine in hypersensitivity reactions to radio contrast media. Clin Exp Allergy. 2010 Mar;40(3):468-75. doi: 10.1111/j.1365-2222.2009.03361.x.
- Bumbacea RS, Petrutescu B, Bumbacea D, Strâmbu I. Immediate and delayed hypersensitivity reactions to intravascular iodine based radiocontrast media – an update. Pneumologia. 2013 Jan-Mar;62(1):47-51.
- Weinstabl A, Amann PM, Wurpts G, Merk HF. Iodine allergy. Hautarzt. 2012 May;63(5):360-3. doi: 10.1007/s00105-012-2372-5.
- Kunze J, Kaiser HJ, Petres J. Relevance of an iodine allergy to commercial polyvidone-iodine preparations. Z Hautkr. 1983 Feb 15;58(4):255-61.
- Moussa LM, Nabhane L, Smayra T, Zebouni SH, Mohanna A, Abi Khalil S, Aoun N. Immediate hypersensitivity reactions to iodinated contrast agents used in radiology: a review. J Med Liban. 2012 Jul-Sep;60(3):159-63.