According to a nationwide survey, nearly 7 million Americans, about 2.3% of the U.S. population, has a seafood allergy.  Shellfish allergy constitutes 1-50 people, while 1-250 have a fish allergy.

Seafood allergy usually develops in late childhood and adulthood and is usually long-lasting.  Seafood allergy can cause mild symptoms, such as hives or lip and tongue swelling, or more sever, even life-threatening symptoms, such as hypotension, dizziness, nausea, wheezing, dyspnea or even loss of consciousness.

Among shellfish, the crustacean group (including shrimp, crab, crayfish, and lobster) is most likely to cause an allergic reaction. Allergies to the mollusk group (including clam, oyster, abalone, mussel, scallop, squid, octopus, and escargot) are less common. Another seafood group, consisting finned fish (including salmon, cod, snapper, mackerel, tuna, grouper, flounder, halibut, trout, and sardines) can also cause food allergies.

Raw fish tends to be more allergenic than cooked fish. Cooking with intense heat can partially or completely destroy the triggering seafood allergen.  This process may explain why some patients who are allergic to fresh fish are able to tolerate canned salmon or tuna.  People with extreme sensitivity, though, can suffer a severe allergic reaction from even trace amounts of seafood or mere exposure to fumes of cooking seafood.

Researchers estimate that a person allergic to one type fish has a 50 percent chance of being allergic to at least one other species of fish.  Furthermore, if they are allergic to shellfish, they have a 75 percent chance of an allergy to another type of shellfish.  Often, shellfish-allergic people can tolerate mollusks.  In general, people suffering an allergy to one seafood group are able tolerate a different seafood group. There appears to be no cross-reaction between finned fish and shellfish.

Allergy to iodine or radiographic contrast media (used in some radiographic procedures), and to shellfish are not related.  If you have an allergy to shellfish, you do not need to worry about cross reactions with radio contrast material or iodine, and vice versa.

The only “cure” for shellfish or fish allergies is to avoid eating the offending fish. Read the labels of every food you eat and avoid sea food restaurants, if you can, since even if you order a non-seafood item off the menu, cross-contact is possible.  Also, shellfish protein can become airborne in the steam released during cooking so you should avoid the seafood cooking area.

Finally, the principal treatment of acute severe allergic reaction is epinephrine. People with all food allergies should carry self-injection devices like EpiPen with them at all times. Seafood allergic reactions may be potentially life threatening and should be taken very seriously, so sufferers should get an appropriate diagnosis and learn how to prevent and treat reactions to ensure safety.