Seafood allergy generally develops in late childhood and is usually long.  Raw fish tends to be more allergenic than cooked fish.  Occasionally, cooking with intense heat can partially or completely destroy the triggering allergen.  This may explain why some patients who are allergic to fresh fish are able to tolerate canned salmon or tuna.

People with extreme sensitivity can suffer a severe allergic reaction from trace amounts of seafood or even merely exposure to fumes of cooking seafood.  The crustacean group (including shrimp, crab, crayfish, and lobster) is most likely to cause an allergic reaction.  Another seafood group consisting scaly fish (including salmon, cod, snapper, mackerel, tuna, grouper, flounder, halibut, trout, and sardines) can also cause food allergies.  Allergies to the mollusk group (including clam, oyster, abalone, mussel, scallop, squid, octopus, and escargot) are less common.

It has been estimated that if a person is allergic to a fish, they have 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 being allergic to another type of shellfish.  However, in general, people suffering from an allergy to one seafood group can tolerate another seafood group.  There appears to be no cross-reaction between fish and shellfish, but simultaneous allergy is possible.  Testing different seafood is the best way to establish an accurate diagnosis.

The only “cure” for shellfish or fish allergies is to avoid the food groups. Read labels of every food you eat.  Reread the labels each time you purchase a product, because manufacturing processes constantly change.  Finally, the principal treatment of acute severe allergic reaction is epinephrine.  People with all food allergies should carry self-injection devices, such as an EpiPen, with them at all times.  After epinephrine is administered, they should be observed for four to eight hours, or overnight in a facility.