Shellfish includes shrimp, lobster, crab, clam, oyster and mussel. Shellfish allergy is more common in adults than in children. Children that are allergic to shellfish are usually not allergic to white fish, salmon and tuna.
Symptoms can occur not only after eating shellfish, but also after contact or from breathing the shellfish vapour during cooking or at a fish market. Usually only a hives or “nettle” rash develops after contact with shellfish. Sometimes as well as a rash, swelling, especially around the face may occur. Some children have an itchy throat; others vomit or can have diarrhoea. Severe reactions are much less common, but can include difficulty in breathing (with wheeze or swelling in the throat), feeling faint or dizzy. Vapours from the shellfish may trigger an asthma attack in children that are allergic.
Allergic reactions are usually mild. Severe reactions affecting the child’s breathing can occur, particularly in those with bad asthma who need urgent medical attention.
Shellfish allergy can sometimes be confused with shell fish poisoning. This is also called ciguatera poisoning. It occurs in warmer weather because of algae in the water. The poison is not destroyed by cooking the shellfish. It generally occurs in seafood with two shells such as clams, oysters, mussels, and sometimes scallops.
Shellfish and fish are different. People who are shellfish-allergic may be able to eat fish. Shellfish are split into two groups: molluscs and crustaceans. Molluscs include Mussels, Clams, Oysters and Squid. Crustaceans include Prawns, Shrimp, Lobster, Crab and Crayfish. People who are allergic to one type of crustacean, such as prawn, are generally allergic to all other crustaceans but may be able to eat molluscs. Your allergist will be able to advise.
The diagnosis of shellfish allergy is based on history of a typical reaction after contact with shellfish. Positive skin prick or blood IgE tests support the diagnosis, but should not be used alone, as people can have positive allergy tests but tolerate the shellfish without getting a reaction.
Skin prick tests can be done in clinic provided that the child has not had any antihistamines for a few days. Blood tests are not affected by antihistamines, but the results are only available in a week or so after the clinic appointment. If the diagnosis is uncertain an oral shellfish challenge is sometimes recommended.
Shellfish is easy to avoid. Some foods, such as Worcestershire sauce, steak sauce, fried rice, egg rolls, salad dressings, seafood muffaletta sandwiches can have shell fish as hidden ingredients. Cross contamination when buying fresh shellfish over the counter in shops and supermarkets can occur. Some dishes like paella, bouillabaisse, gumbo and frito misto contain lots of different kinds of fish at once, can be difficult to spot. It is useful to avoid such dishes.
Some face creams and health supplement can have crushed shells and should be watched for.
A written management plan will be provided and appropriate medication prescribed which should be available at all times.
If shellfish is accidentally eaten spit the food out straight away and give an antihistamine as soon as possible.
- Difficulty breathing (wheezing, noisy breathing)
- Swelling in the throat (noisy breathing, drooling)
- Feeling faint or dizzy, looking very pale (lie the child down with their legs raised).
If any of these severe symptoms occur get help straight away and dial 999 stating “anaphylaxis” (ana-fil-ak-sis).
It is important to inform the nursery/school and any after school clubs. Any other carers such as grandparents, relatives and school friends’ parents will also need to know.
Most children with shellfish allergy will not outgrow the problem. If there has been no reaction for a long time and allergy tests to fish are negative an oral challenge may be suggested.
There is no cure for shellfish allergy at present.