Iodine Allergy: What You Should Know

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Iodine is a nutrient that is essential for thyroid function. Iodine can be found in fish, shellfish, iodine-based contrast agents used in medical imaging (substances taken into your body to enhance images, making them easier to read), and some disinfectant products. 

In the past, it was believed that people who experienced an allergic reaction to substances containing iodine were allergic to the nutrient. Healthcare providers now believe that the term, “iodine allergy” should no longer be used because it is inaccurate.

Iodine is essential for thyroid function, and an allergy to it would be life-threatening. Research shows that iodine is likely not an allergen and that other substances in items also containing iodine are responsible for any hypersensitivity reactions people may have.

This article will explain why some people experience allergic reactions to iodine-containing substances and how to manage the symptoms. 

Woman taking medication with a glass of water in hand.

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Symptoms

If you have an allergy to fish or shellfish, you may have been told that you have an iodine allergy. However, hypersensitivity reactions to fish and shellfish are likely caused by the protein tropomyosin, not iodine. 

Possible symptoms of a reaction to shellfish include:

  • Vomiting
  • Diarrhea 
  • Hives
  • Itching
  • Swelling
  • Wheezing
  • Trouble breathing
  • Dizziness
  • Fainting 

Reactions to iodized contrast agents were considered iodine allergies in the past. However, these reactions are likely caused by another component of the contrast. Symptoms of an allergic reaction may include:

  • Hives
  • Itching
  • Wheezing
  • Trouble breathing

If you think you have an intolerance to iodine or experience symptoms, contact your healthcare provider to get tested.

Causes

Because a true iodine allergy is unlikely, allergic reactions to iodine-containing substances are likely caused by a sensitivity to a different element in the substance. Without iodine in our diets, our thyroid gland would not function and produce thyroid hormones. These hormones are responsible for growth, brain development, bone formation, and energy metabolism. Our bodies do not make iodine, and so we need to obtain it from our diets. 

Allergies to seafood, contrast agents, and antiseptic agents have all been diagnosed as iodine allergies in the past. Healthcare providers believe that individuals who experience a hypersensitivity reaction to one or more of these substances are reacting to a protein instead of iodine.

Treatment

An allergic reaction can be life-threatening and requires immediate medical treatment. If you develop difficulty breathing, seek care right away. If you have been diagnosed with an iodine allergy in the past, talk with your healthcare provider to determine which substance caused the reaction. If you can remember, tell your provider the exact symptoms you experienced and how long they lasted. 

To manage a hypersensitivity to contrast agents, let your healthcare team know that you have reacted to this medication in the past. Next time you are in need of an imaging study such as a computed tomography (CT) scan, your provider will discuss a plan with you.

Often people with a history of allergic reactions are treated with medications to prevent a reaction before the procedure. It is estimated that out of 100 million CT scans performed each year, only about 1% to 3% of patients experience a hypersensitivity reaction.

Foods to Avoid 

If you have ever experienced an allergic reaction to seafood, talk with your healthcare provider about the kinds of fish and shellfish to avoid. Individuals with a shellfish allergy should avoid mollusks like clams, mussels, and oysters, as well as crustaceans like crab, lobster, and shrimp. 

Iodine is naturally found in dairy products and seafood. It is also added to other foods like table salt. 

Misconceptions

Healthcare providers now believe that an iodine allergy is not caused by iodine at all. What was once thought to be an iodine allergy is most likely a hypersensitivity to a protein. 

A shellfish allergy is believed to be caused by a sensitivity to the protein tropomyosin. An allergy to disinfectants or contrast is believed to be caused by another ingredient in the substances. Talk with your healthcare provider if you have questions about your risk of allergy. 

Summary

Iodine is a vital nutrient that is needed for thyroid function. It is unlikely for an individual to be allergic to iodine because the nutrient is needed to sustain life. Allergies to shellfish are likely caused by a hypersensitivity to the protein tropomyosin, rather than iodine. An allergic reaction is a medical emergency and requires immediate treatment. 

A Word From Verywell 

If you have ever been diagnosed with an iodine allergy in the past, you may be feeling understandably confused. As research evolves and we learn more about allergies and hypersensitivity reactions, most healthcare providers feel confident that a true iodine allergy is unlikely. To better understand your risk, talk with your healthcare provider about any past allergic reactions. 

Frequently Asked Questions

  • What is the correlation between shellfish and iodine allergy?

    In the past, it was believed that people who were allergic to shellfish were reacting to the iodine present in the fish. Experts now know that there is not enough iodine in shellfish to elicit a reaction. People who experience an allergic reaction to fish or shellfish are most likely reacting to a protein found in the fish. 

  • How do I test for an iodine allergy?

    An allergist can test you for an iodine allergy using a skin patch test. However, it is unlikely that anyone is truly allergic to iodine because it is necessary for the body to function. 

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6 Sources
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