Iodine isn’t considered to be an allergen (something that triggers an allergic response) since it is actually necessary for thyroid function.

However, some medications, solutions, or concentrations that contain iodine may cause a person to have an allergic reaction. These reactions may be caused by other substances that have been mixed with iodine.

These reactions may or may not be a true allergy to iodine, but people do sometimes call this an “iodine allergy.”

Iodine occurs in some food sources, supplements, and medications. Even an antiseptic solution used to cleanse the skin can cause a skin reaction in some people.

Total body adverse reactions to iodine, or products containing iodine, are rare, but they can be fatal when they do happen.

Iodine also has medical uses. Chemical agents that contain iodine are on the rise, especially in radiocontrast agents used to improve X-ray imaging studies.

Adverse reactions to iodine — when used this way — appear to have occurred over the years. In fact, iodinated contrast dye has been associated with severe reactions and even death in a rare number of cases. But these were not due to an allergy to iodine.

Exposure to mixtures that also contain iodine can cause some of the following reactions:

  • 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 form of anaphylaxis and is life-threatening. It requires emergency medical attention.

Symptoms of anaphylaxis include:

Certain solutions and foods that contain iodine can be the cause of an adverse reaction:

  • Povidone-iodine (Betadine) is a solution commonly used as a skin disinfectant in medical settings. It may cause a rash in sensitive people.
  • Iodinated contrast dye can also cause an allergic reaction. This dye is an X-ray radiocontrast agent used for intravascular injections (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, such as fish and dairy, can also cause an allergic reaction.
  • 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.

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. The researchers concluded that iodine isn’t an allergen.
  • Research shows that people who have a shellfish allergy and people who have an allergy to food other than shellfish, have the same chance of reacting to iodinated contrast dye.
  • 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 polyvinylpyrrolidone 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. 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. After a few days, they’ll check to see if you had a reaction.

Once you’ve been diagnosed with an intolerance to substances that also 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. Your doctor will also direct you to stay away from foods or other things that do 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).

If you’ve had previous experience with allergies or sensitivity to mixtures that contain iodine, discuss your options with your doctor. Avoiding iodine completely could raise these issues:

  • A person can develop an iodine deficiency. This can cause serious health concerns such as thyroid goiter or hypothyroidism. It’s especially concerning during pregnancy and early childhood.
  • A person might avoid or refuse needed treatments because they contain iodine.

Talk to your doctor to determine how you can get enough iodine intake without triggering a reaction.

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