While a healthy source of protein, fish also can cause illness in humans through allergic and non-allergic food reactions. In the United States, allergic reactions to fish occur in 1 in 1,000 children and 1 in 250 adults.
Cause of Fish AllergyThe major allergen responsible for fish allergy is a protein called parvalbumin, which controls the balance of calcium in the white meat of fish. Parvalbumins are very similar between different species of fish – so if a person is allergic to one species of fish, it is very common to be allergic to other fish species as well. Gelatin is another major allergen that is shared among species of fish. When a person who is sensitized to fish comes into contact with or eats fish, an allergic reaction occurs, leading to the symptoms of allergy.
Symptoms of Fish AllergyThe symptoms of fish allergy are similar to those of other food allergies. Almost all people with fish allergy will experience symptoms within an hour of eating the food. The most common symptoms include generalized itching, hives and swelling, vomiting, and respiratory symptoms such as wheezing and chest tightness – although fatal anaphylaxis can also occur. Some people with fish allergy experience hives and itching when they touch raw fish, but are able to eat cooked fish meat without having allergic symptoms. Proteins released into steam when fish is being cooked can also cause allergic symptoms of asthma and hay fever in people with an allergy to fish.
Avoidance of FishMost people with an allergy to one type of fish should avoid eating any species of fish, given that the major fish allergens are shared among many species of fish. It also seems a good idea for people with fish allergy to avoid seafood restaurants, given the chance of contamination of other foods with fish allergen. Fish proteins may also be present in steam released from cooking fish, which may trigger allergic reactions in people with fish allergy.
Fish proteins can also be hidden in certain foods, and therefore cause unexpected allergic reactions in people with fish allergy. Anchovies can be found in Worcestershire sauce and Caesar salad dressing, and surimi (processed Alaskan Pollock) is used as a meat-filler in a variety of foods, including sausages, pepperoni sticks, “meatless” hotdogs and imitation crab. Parvalbumin can also be found in frogs. Therefore, people with fish allergy should also avoid eating frog’s legs.
Avoidance of other fish products, such as sushi, caviar, roe, fish oil capsules and cod liver oil would seem prudent in people with fish allergy. Shellfish are not related to fish, and therefore could be eaten by people with fish allergy. However, the danger of cross-contamination between fish and shellfish exists -- meaning that a person with a fish allergy would not want to eat shellfish in a seafood restaurant, since the food could be contaminated with fish.
Diagnosis and Treatment of Fish AllergyThe diagnosis of fish allergy can be made when a person has experienced allergic symptoms after eating fish, and has as a positive allergy test to fish, either with a skin test or a blood test. Skin testing remains the best way to confirm the diagnosis of fish allergy, although blood testing has the advantage of measuring the amount of allergic antibody against fish. The level of allergic antibody to fish can be helpful in determining whether a person actually has a true fish allergy, has possibly outgrown the fish allergy, or may simply be sensitized to fish, but without experiencing allergic symptoms with eating fish.
A form of food poisoning, called scombroid, involves eating spoiled fish containing large amounts of histamine. The symptoms of scombroidosis are virtually identical to symptoms of true food allergy, although allergy testing is negative, since no allergic antibody is present.
The treatment of fish allergy mainly involves the avoidance of fish. If a fish-allergic person eats fish, and experiences an allergic reaction, immediate treatment is required. This often involves the use of injectable epinephrine, such as with an Epi-Pen or Twin-Ject device, although mild reactions may be treated with oral antihistamines. People with fish allergy should wear a Medic-Alert bracelet listing their food allergy information, and should carry injectable epinephrine at all times given the possibility of the accidental ingestion of fish proteins.
Wild LG, Lehrer SB. Fish and Shellfish Allergy. Current Allergy and Asthma Reports. 2005;5:74-79.
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