Shellfish allergy is one of the most common types of allergies. An estimated two per cent of the population of the United States suffers from allergies to shellfish, second only to peanuts. Unlike many allergies, you can't outgrow shellfish allergy. It usually first occurs in adulthood, although many children suffer from it too. The allergy is most common in women and boys and is likely to run in families.
Symptoms of shellfish allergies can show up in minutes or they may take hours. The most common symptoms are hives (or urticaria) and swelling (angioedema). Hives are raised red weals that can appear anywhere on the body, but usually around the stomach, back, thighs, backside, limbs, and face. Those on the torso can be the size of dinner plates. Hives can be quite itchy. Angioedema is where blood cells produce fluid that builds up in the tissues under the skin and results in swelling. Common sites are the lips, tongue and throat, but also the hands and elsewhere.
Other symptoms of shellfish allergy can include tingling in or around the mouth or throat, chest tightness, nasal congestion, wheezing, breathing difficulties, light-headedness, dizziness, fainting, nausea, vomiting, stomach cramps, and diarrhea. Symptoms usually occur each time shellfish is eaten. Potentially the worst symptom is an acute, whole-of-body allergic reaction. This is called anaphylaxis. The worst type is anaphylactic shock where a quick release of histamines and other mediators means fluid leaks into the skin. The blood vessels dilate, causing swelling, including to the throat. This constricts the airways. Blood pressure falls, and pulse can speed up or be faint. Any of the symptoms listed above can also be present. Disorientation can occur as the body goes into shock. Loss of consciousness and death are a risk. Luckily, it's fairly rare.
Any of the shellfish can cause these symptoms. The two main types of shellfish are crustaceans and mollusks. Crustaceans include shrimps, prawns, crabs, crayfish, lobster, sea urchins, scampi, and langoustines. Mollusks include oysters, mussels, clams, squid (calamari), octopus, cuttlefish, scallops, abalone, cockles, whelks, periwinkles, conch, quahogs, limpets, and escargot (snails). A third type is echinoderms, such as sea urchins. The two main groups are biologically dissimilar and, while some people are allergic to one group and not the other, there is high cross-reaction between the two groups. If a person is allergic to a certain shellfish, they are 75 per cent likely to be allergic to others. Shrimps are worst as an allergenic, although there are cases where a person is allergic to some types of shrimps but not others. There is also a cross-reaction between shellfish and certain insects. No cross-reaction exists between shellfish and fish, although people can be allergic to both food types.
Shellfish allergies are caused by the proteins in the flesh. The main allergy-causing protein in shellfish is tropomyosin. The immune system produces antibodies against the allergen, causing the release of histamines and other chemicals. Tropomyosin is also found in some supplements, as well as in dust mites and cockroaches. Allergies can also be caused by the gelatin in the skin and bones of shellfish. Getting sick from shellfish might not be allergy, but food poisoning from toxins or bacteria in the shellfish. Symptoms are similar, though the immune system isn't involved.
People with shellfish allergies can get relief from antihistamine tablets such as loratadine (Claratin) or diphenhydramine (Benadryl). Calamine lotion eases the itchiness associated with hives. Another way is to put ice on the hives as this shrinks the blood vessels and reduces swelling. Milk of magnesia may help reduce symptoms, as can peppermint tea. For severe symptoms, it might be possible to receive an epinephrine injection from your doctor. It's always best to see a doctor while the symptoms are present. Skin and blood tests can be conducted for shellfish allergy. With skin prick tests, you can be tested for allergies to each type of shellfish. A blood test can measure antibodies in the blood to see how the immune system responds to shellfish protein. It's also a good idea to wear an alert bracelet.
People with allergies to shellfish have to be careful to avoid a range of situations and prepared foods. The best way for sufferers to avoid shellfish allergies is of course to avoid shellfish altogether, but this can be difficult. If you eat at restaurants, you need to be aware of the possibilities for cross-contamination. A chef may use the same pans and utensils for cooking shellfish and other food such as fries or chicken, or these foods might be cooked in the same oil. Cross-contamination can occur in factories too, where equipment used for one product is then used for another. Beware of foods that may contain shellfish, such as bouillabaisse, fish stock, flavorings, cuttlefish ink, surimi, etouffee, gumbo, cioppino, jambalaya, chili, and various sauces or dressings.
Some people can become quite ill after consuming no more than a trace of shellfish. Or they can be affected by the steam from the cooking process as the allergy-causing proteins can be airborne. This applies equally in restaurants and at home. If someone in the household is allergic to shellfish, it is best to move them well away from the kitchen when another family member is cooking shellfish. Further, symptoms can occur merely from handling or touching shellfish.
It might be a good idea to avoid coral calcium supplements as these have the same protein as shellfish. Omega-3 may contain shellfish, although fish is more usual, such as cod liver. Also avoid food containing gelatin. Glucosamine is a food supplement for arthritic patients that is often put forward as a problem for people with shellfish allergies. This is rarely the case as it is made of crustacean shells as distinct from the flesh, which is the location of the problem proteins. Vegetarian glucosamine is available in any case. Glucosamine actually occurs naturally in the body and helps repair healthy cartilage. Some sources say there is an allergy connection between IV dye and shellfish. This is a myth. The only connection is that both contain iodine. Reaction from IV dye isn't really an allergic reaction as the dye causes histamine release without assistance from allergic antibodies.
Labeling laws were changed in the United States in 2006 with the Food and Drug Administration's Food Allergy Labeling and Consumer Protection Act, which specifically relates to crustacean shellfish among other foods that typically cause allergies. Labeling laws now require labels to be in plain, simple English that a seven-year-old can read. The term "may contain traces" has been banned. Instead, products that include shellfish have to state this on the label as "contains " either separately in bold or after other ingredients. Shellfish isn't usually a hidden ingredient in food products at any rate. Food labeled as Kosher will have no shellfish, in line with the Kosher diet.
Shellfish allergy and its symptoms can be quite alarming. Symptoms range from unpleasant hives and swelling to life-threatening whole-of-body reactions. Avoidance of seafood altogether is the best option. Care should be taken when eating at restaurants. Check the ingredients on food labels. Your doctor will be able to offer appropriate treatment, including tests and medication.