Iodine Allergy: Myth or Reality?
Iodine is a trace mineral that is required for the synthesis of thyroid hormones regulating the body’s metabolic energy and basal metabolic rate. However, some people think that they have an iodine allergy.
This chemical element is present in many body tissues, but it’s not produced in the body, which makes it a vital micronutrient and essential part of your diet. If you don’t consume enough iodine, you may develop an iodine deficiency. Fortunately, iodine deficiency can be easily corrected by resupplying the trace mineral in the diet.
Does Iodine Allergy Exist?
More and more people are talking about a so-called “iodine allergy”, which usually refers to a history of allergic reactions to iodinated contrast media or povidone-iodine antiseptics.
Some people do experience mild to severe allergic reactions to iodinated antiseptics, iodinated radiological contrast media, iodine-containing medications and iodine-rich seafood. However, “iodine allergy” will not be an accurate label for these reactions.
According to experts, iodine is not an allergen, and the reactions to iodinated products are likely to be related to other substances and molecular components that were mixed with this element, rather than iodine itself.
In fact, a true iodine allergy does not exist, since an allergic reaction to elemental iodine or simple iodide salts (such as potassium iodide) is theoretically impossible.
There is also a common misconception, according to which the iodine content of fish and shellfish causes an allergy to seafood. As a result, the use of iodinated radiological contrast media is often contraindicated in people with seafood allergies.
However, a seafood allergy is not anyhow related to iodine content. Although seafood does contain higher levels of iodine, its allergenic proteins are not iodinated. Knowing this can prevent specialists and their patients from denying useful procedures unnecessarily.
Allergic Reactions to Iodinated Antiseptics
Povidone-iodine is a combination of polyvinylpyrrolidone (povidone or PVP) and iodine, which is present in some types of topical antiseptics. In this complex, diatomic iodine provides a bactericidal effect, while povidone, which is a polymer, helps to deliver the iodine to the bacterial cell surface.
In some people, povidone-iodine may trigger a contact or irritant dermatitis. Although this is rare, and povidone itself is not considered to be a cause of the reaction, there have been reported cases of allergic reactions to some of the povidone’s non-iodinated copolymers (e.g. PVP-eicosene or PVP hexadecane).
When it comes to systemic reactions to povidone-iodine, there have been a few cases of generalized urticaria and even anaphylaxis. These reactions were found to be IgE-mediated, and in one case, researchers identified specific IgE against povidone.
Besides, povidone alone without iodine has also been reported to cause anaphylaxis. In case of anaphylactic reactions to povidone-iodine, patients had positive allergy tests only with povidone.
Therefore, people with a history of allergic reactions to povidone-iodine antiseptics were actually allergic to povidone alone. The reactions were not related to the iodine.
Allergic Reactions to Iodine-Containing Medications
Certain drugs, such as amiodarone, contain iodine. People who have hypersensitivity to amiodarone should avoid the medication. However, no evidence shows that iodine is responsible for allergic reactions triggered by amiodarone.
Besides, other iodine-containing compounds are not contraindicated in people with hypersensitivity to amiodarone.
Allergic Reactions to Iodinated Radiocontrast Media
Radiocontrast media include tri-iodinated benzoic acid derivatives containing small amounts of free iodide.
Non-idiosyncratic reaction to these media are likely to be caused by direct toxic or osmolar effects. Iodide mumps and other manifestations of iodine poisoning are the only adverse effect of contrast material related to free iodide.
While idiosyncratic reactions to radiocontrast media are not common, they may include immediate and non-immediate hypersensitivity-type reactions. Immediate reactions involve allergy symptoms like pruritus (itching), urticaria (hives), angioedema, and even anaphylaxis. Non-immediate reactions occur about an hour after administration, and they often include skin reactions like urticaria, angioedema, maculopapular rash, or, in rare cases, Stevens-Johnson syndrome.
Allergy-type reactions to radiocontrast media have created the misconception that the allergy is caused by iodine itself. However, experts confirm that iodine is not the culprit in these reactions.
What Are the Risk Factors in Reactions to Contrast Media?
According to some studies, having seafood allergy does slightly increase the risk of developing an allergic reaction to radiocontrast media. However, seafood sensitivity should not be considered a specific risk factor. In fact, being allergic to food in general can also contribute to the risk, as well as having severe hay fever or asthma.
Another study found that cardiovascular disease, asthma and the use of beta-blockers increase the risk of severe reactions.
Yet, the only significant risk factor in this case is a history of a previous severe reaction to contrast media.
In addition, a history of drug allergy, contact hypersensitivity or contact allergy to iodinated antiseptics can increase the risk of a non-immediate reaction, but it’s not a contraindication to the use of contrast media. Reactions to povidone-iodine have nothing in common with contrast media, because povidone has a different structure, with or without iodine.
How to Use Contrast Media in People with Risk Factors?
To identify the risk factors in a patient before using contrast media, a specialist should ask some questions about severe food allergies, drug allergies, asthma, cardiovascular disease or the use of beta-blockers in the patient.
If the patient does have any of these risk factors, the procedure should be closely monitored by a professional who is ready to treat a reaction. Giving low-osmolarity non-ionic contrast media can help to reduce the risk of a reaction.
Premedication can also be helpful, but there are several case reports showing that premedication fail to prevent anaphylaxis. Finally, if the risk is high, other diagnostic testing methods may be more suitable.
The Bottom Line
No evidence confirms that allergic reactions to iodinated products and iodine-containing food and drugs are caused by the iodine itself. In fact, allergic reactions to elemental iodine or simple iodine salts are theoretically impossible. According to research, these reactions are most likely to be triggered by other molecular components.
Besides, seafood allergy is not related to the iodine content either. Even though fish, crustaceans and molluscs do contain high levels of iodine, an allergy to seafood is caused by non-iodinated proteins. If you have a seafood allergy and are worried that you may react to iodinated contrast media, talk with your doctor about the risks.