Allergies related to eating shellfish are quite common, accounting for about a third of all food allergy cases.
However, people who think they are allergic to fish and shellfish show huge discrepancies in terms of symptoms, ranging from milder ones like reddish and itchy skin, rashes, swelling of lips, and diarrhea, to more serious and even life-threatening ones such as swelling of the throat, wheezing breath and shock.
In fact, if one falls ill after eating seafood, it may or may not be a case of allergy.
Symptoms attributed by allergic reactions normally surface after around two hours from the intake of the allergen.
Those who feel unwell a day after consuming great quantities of shellfish, for example, may be suffering from seafood intolerance rather than seafood allergy.
Histamine, an organic nitrogenous compound that is given out by the body in response to an injury or allergy, is responsible for causing adverse reactions in people who are exposed to certain substances that they are allergic to.
Fish and shellfish could also contain high levels of histamine. That’s why sometimes there’s a lag between the time individuals take in a large amount of seafood and the time they start feeling unwell.
Common symptoms of seafood intolerance include itchy skin, raised itchy red rashes and diarrhea.
Meanwhile, allergies to shellfish may be divided into two major types based on the classification of the aquatic invertebrates – crustaceans (e.g. crabs, lobsters, crayfish, shrimps, prawns) and mollusks (e.g. oysters, clams, snails, squids).
Patients could react to only one type of shellfish, but it is very likely for them to react to other members of the group.
They are advised to avoid that particular item to which they are allergic as well as the rest of the group to which it belongs.
About 75 percent of people in Hong Kong who are allergic to house dust mite also react to seafood because of the intake of tropomyosin – a muscle protein which is common in crustaceans and mollusks.
In order to confirm seafood allergy, patients are given some tests, which could be a skin-prick test or an allergen-specific immunoglobulin E (IgE) blood test.
If the result of either test is positive, it suggests that patients are reactive to the testing substance(s), meaning certain shellfish types.
June Chan King-chi, a subcommittee member of the Hong Kong Institute of Allergy (HKIA), is also the author of this article, which appeared in the Hong Kong Economic Journal on Sept. 7.
Translation by Darlie Yiu
[Chinese version 中文版]
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