Iodine isn’t considered to be an allergen, which is anything that triggers an allergic response. But some people are intolerant to substances closely mixed together with it. This may or may not be a true allergy, and these people may loosely call this intolerance an “iodine allergy.”

Iodine is a common element found in the human body. Adverse reactions to iodine are rare, but they can be fatal when they do happen.

Medical uses of chemical agents that contain iodine are on the rise, especially in radiocontrast agents used to improve X-ray imaging studies. As a result, adverse reactions to iodine when used this way have occurred over the years. Iodinated contrast has been associated with severe reactions and even death in a rare number of cases, but these weren’t due to an allergy to iodine.

Exposure to things that may happen to contain iodine can cause some of the following in hypersensitive people:

  • itchy rash that comes on slowly (contact dermatitis)
  • hives (urticaria)
  • anaphylaxis, which is a sudden allergic reaction that can cause hives, swelling of your tongue and throat, and shortness of breath

Anaphylactic shock is the most severe, life-threatening form of anaphylaxis. It requires emergency medical attention.

Symptoms of anaphylaxis include:

  • abdominal pain
  • nausea or vomiting
  • diarrhea
  • confusion
  • altered level of consciousness
  • dizziness
  • lightheadedness
  • hives
  • difficulty breathing
  • heart palpitations
  • rapid pulse
  • low blood pressure

Certain solutions and foods containing iodine can cause an adverse reaction:

Povidone-iodine (Betadine), a solution commonly used as a skin disinfectant in medical settings, may cause a rash in sensitive people.

Iodinated contrast dye can also cause an allergic reaction. It’s an X-ray radiocontrast agent used for intravascular injections (that is, injections into blood vessels).

Contrast dyes containing iodine have been responsible for severe reactions (including deaths) in a very limited number of people. Those who have an allergy or other adverse effect to iodinated radiocontrast dye may be given systemic glucocorticosteroid before receiving iodinated contrast. Or use of iodinated contrast may be avoided altogether.

Foods that contain iodine can also cause an allergic reaction. Fish and dairy are sources of iodine.

There are some myths about what actually causes an intolerance to iodine-containing substances.

Many people believe that you’ll be at risk for having an adverse reaction to iodine if you have a shellfish allergy. This is largely a misconception. According to a study published in the Journal of Emergency Medicine, shellfish allergies aren’t linked to an allergy to iodine, as the researchers concluded that iodine isn’t an allergen.

Research also shows that having a shellfish allergy doesn’t increase the likelihood that you’ll have a reaction to intravascular contrast containing iodine compared to people with an allergy to something other than shellfish. Instead, proteins such as parvalbumins in fish and tropomyosins in shellfish are responsible for seafood allergies.

Some topical antiseptics contain povidone-iodine. This is a solution of polyvinyl pyrrolidone and iodine. Povidone-iodine can cause a serious rash that’s similar to a chemical burn in a few rare cases. In some, the rash may be just a simple skin irritation, but in others, the rash could be part of an allergic reaction.

In patch tests, however, allergic reactions weren’t caused by the iodine. Instead, they were caused by non-iodinated copolymers in povidone. Povidone exposure has been known to result in contact dermatitis or, in very rare cases, anaphylaxis.

Your doctor may have you do a patch test if they think you’re allergic to the povidone in povidone-iodine solution. During a patch test, your doctor applies a small amount of povidone-iodine to a patch. It’s then placed on your skin. They’ll check to see if you had a reaction after a few days.

Once you’ve been diagnosed with an intolerance to substances that contain iodine, your doctor may prescribe a corticosteroid cream or oral corticosteroid such as prednisone. These can help relieve symptoms, such as an itchy rash. They’ll also direct you to stay away from foods or other things that trigger these adverse reactions.

Anaphylactic shock is an emergency situation. It may require immediate medical treatment in the form of a shot of epinephrine (adrenaline).

Amiodarone (Cordarone, Pacerone) is a medication that’s used to manage atrial fibrillation and other heart rhythm diseases in those with cardiac conditions. Currently, experts know of only one case of suspected cross-reactivity in a person who received amiodarone and iodine-containing contrast. Doctors should use caution when prescribing amiodarone for people who have problems with iodine-containing contrast. However, the risk of a true allergic reaction is very low.

While iodine intolerance and adverse side effects to intravascular contrast dye that contains iodine are uncommon, talk to your doctor about getting tested if you suspect you have a problem with either or suffer from some of the symptoms.

If you’re diagnosed with an intolerance to certain types of foods, work with your doctor on a diet that will help you to avoid reactions.