Although iodine is not generally considered an allergen, some people are hypersensitive and may be considered to have an iodine "allergy."
Iodine is a common element found in, among other places, the human body, so reactions to iodine are extremely rare. But they do happen. With medical uses of iodine on the rise—especially as radio contrast media—more instances of reactions have been reported in recent years.
In a few cases, iodine has even been responsible for patient deaths.
In hypersensitive patients, exposure to iodine may cause a rash (contact dermatitis), hives (when ingested), or, very rarely, anaphylaxis. Anaphylactic shock is a life-threatening condition that requires emergency medical attention.
Symptoms of anaphylaxis include:
- abdominal pain
- difficulty breathing
- heart palpitations
- hives (along with other symptoms)
- nausea or vomiting
- rapid pulse
Tincture of iodine (also known as weak iodine solution) is commonly used as a disinfectant in medical settings and may cause rashes in hypersensitive people.
Shellfish Allergies and Iodine
A 2005 study published in the journal Allergy and Asthma Proceedings found an almost universal misconception about the relationship between iodine and shellfish allergies. Among parents and patients who had visited a pediatric clinic due to a suspected shellfish allergy, 92 percent believed that the allergy was caused by iodine in the seafood. However, that simply isn't the case.
Multiple studies have shown that seafood allergies have nothing at all to do with iodine. Proteins such as parvalbumins in fish and tropomyosins in shellfish are responsible for seafood allergies. The myth has gained so much traction, however, that, in another survey, one third of U.S. radiologists and 50 percent of cardiologists believed it—telling researchers they would withhold contrast media containing iodine if a patient had been diagnosed with a shellfish allergy.
According to the researchers in a 2010 study published in the Journal of Emergency Medicine, "Allergies to shellfish, in particular, do not increase the risk of reaction to intravenous contrast any more than that of other allergies."
Some topical antiseptics contain povidone-iodine, a solution of polyvinylpyrrolidone (PVP) and iodine. In rare cases, povidone-iodine may cause serious contact dermatitis akin to a chemical burn.
In patch tests, however, positive allergic reactions were not due to the iodine, but rather non-iodinated copolymers in povidone (PVP-eicosene and PVP hexadecane).
In very rare cases, povidone alone has resulted in anaphylactic shock in some patients.
Iodine Allergy Test
A patch test is usually done if iodine hypersensitivity is suspected. A small amount of iodine is applied to a patch, which is then placed on a patient's skin and checked for a reaction.
Iodine Contrast Allergy
As a heavy element, iodine is "radio-opaque" and, therefore, often used as an X-ray radiocontrast agent for intravenous injections. Contrast dyes containing iodine have been implicated in allergy-like anaphylactoid reactions in a small number of hypersensitive patients.
As mentioned above, many people believe there is a cross-reactivity between shellfish allergies and iodinated contrast media but research does not bear out the connection.
A clinician may prescribe a corticosteroid cream or oral corticosteroid such as prednisone to relieve symptoms of an iodine hypersensitivity (such as a rash).
A patient experiencing anaphylactic shock will require immediate medical treatment in the form of a shot of epinephrine (adrenaline).
Amiodarone and Iodine Allergy
Amiodarone is a class III antiarrhythmic agent used to manage atrial fibrillation in cardiac patients. Thus far, only one case of cross-reactivity between amiodarone and iodine hypersensitivity has been published. Physicians should use caution when prescribing amiodarone for such patients. However, the risk of an allergic reaction is probably negligible.