The Allergy Clinic
Specialists in Allergy & Asthma Care
Specialists in Allergy & Asthma Care
Iodine Dye Allergy
At least once a week, we hear a patient tell us that they are scared to eat fish or shellfish because they had an allergic
reaction to iodine. The next part of the story involves the Radiology procedure they underwent when they had the
reaction.
Let’s untangle two myths and shed some light on this:
1) Radiocontrast media (RCM) that contains organic iodine may cause adverse reactions such as urticaria,
angioedema, bronchospasm, laryngospasm and shock. These reactions are not truly allergic in origin. Instead, a non-
allergic pathway triggers what looks exactly like an allergic reaction. While we don’t know the exact mechanism, it is
apparently related to the high osmolarity of these agents. If you have had this type of reaction and need another
procedure done, your physician will probably recommend a lower osmolar preparation to decrease the risk of another
reaction.
The risk can be further decreased by pre-medicating with antihistamines
(e.g., Allegra, Claritin/Clarinex or Zyrtec) and steroids (e.g., prednisone). I don’t recommend Benadryl anymore for
outpatient pre-medication protocols. The risk of tolerating the procedure just fine, but then falling asleep and crashing
your car into a tree on the way home must also be considered.
2) Seafood may contain iodine. However, seafood allergy is not caused by iodine; rather, to specific proteins in fish
and shellfish (e.g., parvalbumin, tropomyosin) that also do not contain iodine. Thus, fish or shellfish allergy does not
indicate a sensitivity or allergy to iodine.
Many thanks to the American Academy of Allergy, Asthma & Immunology’s News for providing this update. Their
website is a terrific source for physicians and health consumers.
American Academy of Allergy, Asthma & Immunology's Patient Site
At least once a week, we hear a patient tell us that they are scared to eat fish or shellfish because they had an allergic
reaction to iodine. The next part of the story involves the Radiology procedure they underwent when they had the
reaction.
Let’s untangle two myths and shed some light on this:
1) Radiocontrast media (RCM) that contains organic iodine may cause adverse reactions such as urticaria,
angioedema, bronchospasm, laryngospasm and shock. These reactions are not truly allergic in origin. Instead, a non-
allergic pathway triggers what looks exactly like an allergic reaction. While we don’t know the exact mechanism, it is
apparently related to the high osmolarity of these agents. If you have had this type of reaction and need another
procedure done, your physician will probably recommend a lower osmolar preparation to decrease the risk of another
reaction.
The risk can be further decreased by pre-medicating with antihistamines
(e.g., Allegra, Claritin/Clarinex or Zyrtec) and steroids (e.g., prednisone). I don’t recommend Benadryl anymore for
outpatient pre-medication protocols. The risk of tolerating the procedure just fine, but then falling asleep and crashing
your car into a tree on the way home must also be considered.
2) Seafood may contain iodine. However, seafood allergy is not caused by iodine; rather, to specific proteins in fish
and shellfish (e.g., parvalbumin, tropomyosin) that also do not contain iodine. Thus, fish or shellfish allergy does not
indicate a sensitivity or allergy to iodine.
Many thanks to the American Academy of Allergy, Asthma & Immunology’s News for providing this update. Their
website is a terrific source for physicians and health consumers.
American Academy of Allergy, Asthma & Immunology's Patient Site
