Author: Marie Hartley, Staff writer, 2010.

What is iodine?

Iodine is a natural element that is essential for all living organisms. Iodine is a member of a group of non-metal elements called halogens; other halogens include fluorine, chlorine and bromine.

What is iodine used for?

Iodine is used topically, orally and by injection:

Iodine may also be ingested in foods such as seaweed, seafood and iodised salt. Smaller amounts of iodine are found in vegetables and meat.

Iodine allergy

The term ?쁦odine allergy??is commonly used, but is actually a misnomer. Iodine is a trace element present throughout the body, and is essential for the production of thyroid hormones. It is not possible to have a true allergy to elemental iodine.

?쁈odine allergy??usually refers to an allergic-type reaction to iodinated radiological contrast media or, less commonly, an allergic contact reaction to povidone-iodine (Betadine?? antiseptics.

Cutaneous reactions to iodinated radiological contrast media

These reactions may be classified as immediate and non-immediate:

Newer iodinated contrast media have improved chemical properties and the incidence of these types of reactions is now much lower.

Most of the above reactions to contrast media are not true hypersensitivity reactions (immunoglobulin E antibodies are not involved). The reactions are called idiosyncratic, and unlike true hypersensitivity reactions, previous sensitisation to the agent is not required, nor do these reactions consistently recur in an individual.

Risk factors for reactions to contrast media

Risk factorManagement
History of a previous reaction to iodinated contrast media
  • This is the most substantial risk factor for future reactions.
  • Iodinated contrast media should not be used if a previous reaction was severe.
History of asthma, food allergy, or allergy to other medications
  • It is often erroneously thought that seafood allergy precludes the use of iodinated contrast media. However, seafood allergy is unrelated to iodine.
  • Although seafood allergy is not a specific risk factor for a reaction to iodinated contrast media, a history of any moderate or severe allergic disorder increases the risk. Use with caution.
Significant cardiovascular disease or use of beta-blocker medications
  • Use iodinated contrast media with caution.

Allergic contact reactions to povidone-iodine

Povidone-iodine is a commonly used antibacterial agent that is a compound of iodine and povidone, along with other additives. Povidone is also used in other products such as foods, medicines (e.g. antihistamines, diuretics and pain-relievers), hair products and toothpastes.

Allergic contact reactions to povidone-iodine preparations are rare, and can be difficult to distinguish from an irritant contact reaction to povidone-iodine. Both reactions can cause redness, induration (firmness) and multiple small blisters.

Patch testing is often used to help diagnose an allergic contact reaction. However, false positive reactions can occur in this instance due to the irritant properties of povidone-iodine under occlusion. When a positive patch test reaction to povidone-iodine does occur, it is important to confirm results with further tests, such as the repeat open application test (ROAT).

Systemic reactions to povidone-iodine antiseptics (e.g. generalised urticaria and anaphylaxis) are extremely rare and are thought to be caused by povidone, rather than iodine.

Cross-reactivity between povidone-iodine antiseptics and iodinated contrast media

Other cutaneous reactions to iodine

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