Shellfish allergy: Separating fact from fiction
Allergy to shellfish can be serious, and there are many myths surrounding this condition. Here's what you need to know.
Did you know that someone can develop a shellfish allergy even if shellfish has been eaten before without any issues? Allergy to shellfish can be serious, and there are many myths surrounding this condition. Let's separate the facts from the fiction:
1. Myth: Shellfish allergy is common in children.
Fact: Adults are more frequently affected by shellfish allergy than children.
About 2 percent of adults in the United States are allergic to shellfish, while only about 0.5 percent of children are affected.
2. Myth: Patients with shellfish allergy are also allergic to radiocontrast material, which is used in CT scans and other diagnostic tests.
Fact: Patients are not at increased risk for reactions to radiocontrast material if they are allergic to shellfish.
This misconception relates to shellfish having a high iodine concentration, and radiocontrast material also containing iodine. It's true that seafood is rich in iodine. However, patients with seafood allergies react to proteins in the seafood, rather than the iodine. There is no reason to assume that people with seafood allergy cannot be treated with topical iodine or be given radiocontrast media that contains iodine.
3. Myth: If a child is allergic to shellfish, the food needs to be eaten in order to cause a reaction.
Fact: Shellfish allergen can become vaporized, causing reactions even without ingestion of the food.
Most foods linked to serious reactions in patients with food allergy, such as peanuts and tree nuts, need to be ingested in order to cause breathing problems. This is because proteins in these foods do not turn into vapor. For seafood though, it is possible for patients with allergy to develop symptoms such as coughing and/or wheezing when the protein becomes airborne. Thankfully, anaphylaxis due to vaporized seafood allergens is very rare. However, if your child is seafood allergic, it is important to keep areas well ventilated when the food is being cooked around him. Also be aware that your child could have a reaction at a restaurant if breathing in vaporized shellfish protein.
4. Myth: Children who have reactions such as mouth tingling, dizziness, or vomiting when they eat shellfish are allergic.
Fact: Shellfish reactions can be related to poisoning from marine toxins, leading to symptoms that mimic life-threatening allergy.
Being diagnosed with a food allergy has significant effects on a child's life. Not all reactions are due to true allergies though. If your child has had symptoms of illness following ingestion of shellfish or seafood, it is important for an allergist to be involved in diagnosis and treatment. Skin testing for the suspected allergy can be used to help figure out if your child is truly allergic or had some other type of reaction to the food.
5. Myth: People with shellfish allergy are allergic to all seafood.
Fact: The proteins that cause allergic reactions to shellfish are different from those in finned fish, such us tuna, salmon, cod, and tilapia.
It is quite possible to be allergic to shellfish, but not finned fish, and vice versa. Some children may be allergic to certain shellfish called crustaceans (crab, shrimp, lobster), but not allergic to a different type of shellfish called mollusks (clams, calamari, scallops, mussels). For many children, being allergic to one type of shellfish may mean it is best to avoid all types of shellfish. This is due to the potential of cross-contamination of one type of shellfish with other types during processing and preparation, especially at restaurants.
The quality of life for a child and family must always be considered though. For example, for a child who tests positive for allergy to crustaceans after a reaction to shrimp, and tests negative for allergy to mollusks, the family might decide to keep mollusks that have been carefully prepared at home in the diet, while strictly avoiding crustaceans. Such a decision should only be made after consultation with an allergist, due to potential risks associated with this management approach.
Shellfish allergy is rare in children, more often diagnosed in adults, and not likely to be outgrown. If your child has had a reaction to shellfish, it is important testing be completed by an allergist to confirm the allergy, since symptoms of illness can be caused by toxins rather than by allergy-causing proteins.
The most reliable allergy testing involves a small scratch to the skin using a tiny prick device containing the allergen in question, with results available in as little as 20 minutes. If skin testing is negative, the allergist might double check the result with a blood test, and then carefully reintroduce the food in question during an in-office challenge, before the allergy can be fully ruled-out. A challenge involves a patient eating small increasing doses of the suspected allergen over a period of time while being carefully monitored for a reaction. If testing is positive, and an allergist confirms the allergy, it is very important to strictly avoid the food, have two doses of autoinjectable epinephrine available at all times, and have a food allergy action plan in place at home and school.
For more information:
Food Allergy Research & Education: Shellfish
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