SEAFOOD ALLERGY: ALLERGIC VERSUS TOXIC REACTIONS

Seafood allergy commonly occurs where seafood is an important part of the diet. It is more common in adults than children, and when it occurs, it almost always remains a life-long problem. Some conditions caused by toxins in seafood can resemble allergic reactions to seafood.

Allergic and toxic reactions to seafood often present with similar symptoms, and history alone may not distinguish between these two problems. Both allergic and toxic reactions often begin within thirty minutes of eating the fish meal, and both types of reactions can include itching, flushing, hives, nausea, vomiting, dizziness, breathing problems, difficulty in thinking, and in severe cases, a drop in blood pressure (anaphylaxis).

Toxic reactions, often referred to as scromboid poisoning, are caused by fish improperly refrigerated after capture. One clue that you may have had scromboid poisoning is that the affected fish often has a metallic or peppery taste.

It is important to distinguish whether you have had an allergic or a toxic reaction.

If you are allergic to fish, you must avoid fish indefinitely.

A toxic reaction means that you can eat properly prepared seafood in the future.

The two major groups of seafood that can trigger allergic reactions are:

Vertebrates
- Scaly fish (fin fish - salmon, cod, mackerel, sardines, herring, anchovies, tuna, trout, haddock, snapper, etc.)

Crustaceans (prawns, shrimp, lobster, crab, crayfish)
Mollusks (snail, abalone, clams, oysters, mussel)
Cephalopods (octopus, cuttlefish, squid, calamari)
Gastropods (sea slugs, garden slugs, snails)

Please note that the term “shellfish” is used to encompass both “shelled” fish (oysters), as well as crustaceans.

Seafood Allergy is Most Often Restricted to Only One Seafood Group (Vertebrates OR Invertebrates)

People who are allergic to one scaly fish are often allergic to other scaly fish. Similarly, allergy to one crustacean usually means that all other crustaceans must be avoided. On the other hand, people who are allergic to seafood from one group (i.e., Vertebrates) can usually eat seafood from the other group (i.e., Invertebrates).

If you have a seafood allergy, COMPLETE AVOIDANCE OF THE OFFENDING VERTEBRATE OR INVERTEBRATE IS MANDATORY. In spite of careful questioning, accidental ingestion can occur. Accidental exposure is most likely to occur when eating away from home, particularly when eating at seafood restaurants. Other potential sources of accidental exposure and cross-contamination include:

Seafood platters and smorgasbords.
Asian foods, in which shellfish can be a common ingredient or contaminant (e.g., prawns in fried rice or soups).
Food may be rolled in the same batter or cooked in the same oil as seafood (e.g. take-away fish and chips).
Anchovies in Caesar salads and as an ingredient in Worcestershire sauce.
Conta minated barbeques.
Fish extracts are also occasionally used to remove particulate matter from some beverages such as wine and beer, a process known as “fining.”

SEAFOOD ALLERGY AND IODINE ALLERGY ARE NOT RELATED

Even through seafood is a rich source of natural iodine, allergic reactions to seafood occur because of an abnormal, immune reaction to fish protein (muscle). People who are allergic to seafood are NOT allergic to radiocontrast media dye (RCM) used in x-ray studies. Reactions to the radiocontrast media dye (RCM) are NOT truly allergic in nature, meaning there is no allergy antibody present that causes these reactions. Rather, RCM acts directly on mast cells to release histamine and other chemicals (a non-immune mechanism). Concentration of the RCM dye may be one factor, as high-osmolality contrast media is much more likely to cause an adverse reaction than low-osmolality contrast media.

Glucosamine Is Derived From Shellfish