Introduction
Uses
Iodine allergy
Cutaneous reactions
Risk factors
Allergic contact reactions
Cross-reactivity
Other cutaneous reactions
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.
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.
The term ‘iodine 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.
‘Iodine 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.
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, a previous sensitisation to the agent is not required, nor do these reactions consistently recur in an individual.
Risk factor |
Management |
|
|---|---|---|
History of a previous reaction to iodinated contrast media |
|
|
History of asthma, food allergy, or allergy to other medications |
|
|
Significant cardiovascular disease or use of beta-blocker medications |
|
|
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 (eg, antihistamines, diuretics, and pain-relievers), hair products, and toothpaste.
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.
Approved datasheets are the official source of information for medicines, including approved uses, doses, and safety information. Check the individual datasheet in your country for information about medicines.
We suggest you refer to your national drug approval agency such as the Australian Therapeutic Goods Administration (TGA), US Food and Drug Administration (FDA), UK Medicines and Healthcare products regulatory agency (MHRA) / emc, and NZ Medsafe, or a national or state-approved formulary eg, the New Zealand Formulary (NZF) and New Zealand Formulary for Children (NZFC) and the British National Formulary (BNF) and British National Formulary for Children (BNFC).
