Even though fish and shellfish live in the same place, the protein allergens present in one seafood group are generally considered to be very different to those in others. That means that one can be allergic to fish only, shellfish only or members of both groups. People who are allergic to one fish are usually but not always allergic to most other fish.
Similarly, allergy to one crustacean usually means that all must be avoided. While those allergic to seafood from one group e. Similarly, people allergic to crustaceans may also be allergic to edible insects such as crickets that may be used as cricket flour in baked goods. Cross reactivity means that a similar protein is present in a range of different foods. If the same protein is present in several foods, then that person may have allergic reactions to any food containing that protein.
Examples of cross reactivity include people allergic to similar proteins present in one fish that are also present in other fish, or those allergic to proteins present in prawn, crab and lobster.
Unfortunately, it is sometimes difficult to predict whether a person will be allergic to one unique protein allergen present in one food only , or several similar cross reactive proteins present in multiple foods, simply based on whether foods have a similar appearance.
Therefore it is not possible to reliably predict the likelihood of allergy to one or more seafood group or individual seafood species without specific testing. Seafood allergens are usually very heat stable and cannot easily be destroyed through cooking, although occasional individuals seem to tolerate tinned fish intensely heat treated , yet are unable to tolerate the same fish freshly cooked. Do not try tinned fish unless advised by your allergy specialist.
Occupational asthma and contact rashes can also be a problem where exposure is frequent, such as in seafood processing factories, or in some food handlers such as chefs. Allergic symptoms after contact with seafood are usually within minutes, however, delayed type reactions and particularly exercise-induced anaphylaxis is occasionally observed, particularly after ingestion of shellfish such as oyster, abalone, squid and shrimp.
Complete avoidance of one or more groups of seafood is often advised, yet this can be difficult. Accidental exposure is more likely to occur when eating away from home, particularly when eating at seafood restaurants.
People allergic to seafood have allergic reactions to proteins present in the animal, not to iodine , which may be present as well. People who are allergic to seafood are not at an increased risk of allergic reactions to iodine e. Conversely, people with iodine allergy are not at increased risk of seafood allergy. Glucosamine is a popular complementary medicine, used to treat osteoarthritis, which is derived from the outer coatings of shellfish such as crustaceans.
Sometimes chondroitin sulphate is added, usually derived from shark cartilage. While people allergic to shellfish are sensitive to protein and not shell constituents, tests to exclude protein contamination are not routinely performed and there is little proof of safety in people with shellfish allergy, although challenge studies of small numbers of patients have demonstrated tolerance.
This risk is considered to be very low. Your doctor will normally ask a series of questions that may help to narrow down the list of likely causes of allergy such as foods or medicines consumed that day, or exposure to stinging insects. This approach will also help to exclude conditions that can sometimes be confused with food allergy. Skin or blood allergen specific IgE allergy tests help confirm or exclude potential triggers. While the results of allergy testing are a guide to whether the person is allergic, results are not a reliable guide to whether the reaction will be mild or severe.
It is also important to be aware that it may not be possible to test for all seafood species using commercial skin prick or blood allergy testing, since these are not available for all seafood species.
For this reason, some allergy clinics will recommend that you bring samples of fresh food for testing. Most of the time, children with food allergy do not have parents with food allergy. However, if a family has one child with food allergy, their brothers and sisters are at a slightly higher risk of having food allergy themselves, although that risk is still relatively low.
Some parents want to have their other children screened for food allergy. If the test is negative, that may be reassuring, but does not mean that the other child will never develop an allergy later. If their screening test is positive, it is not always clear whether it definitely represents allergy, or whether the sensitisation detected by the test is clinically irrelevant.
The term "false positive" is sometimes used to describe this. It is important to know that a positive skin or blood allergy test means that the body's immune system has produced a response to a food, but sometimes these are false positives. In other words, the test may be positive yet the person can actually eat the food without a problem. A serious reaction is an emergency. Give yourself an epinephrine shot. Make sure it is with you at all times. To prevent future reactions Avoid the foods that cause problems.
And try not to use utensils or cookware that may have been in contact with food that you are allergic to. Teach your family members, co-workers, and friends what to do if you have a severe reaction to a food that you are allergic to.
Wear medical alert jewellery that lists your allergies. Give an epinephrine shot if: You think you are having a severe allergic reaction.
For example, call if: You have symptoms of a severe allergic reaction. These may include: Sudden raised, red areas hives all over your body. Swelling of the throat, mouth, lips, or tongue. Trouble breathing. Passing out losing consciousness. Or you may feel very light-headed or suddenly feel weak, confused, or restless. Some people with shellfish allergies are allergic to both groups, but some are allergic only to one.
Most allergic reactions to shellfish happen when someone eats shellfish. But sometimes a person can react to touching shellfish or breathing in vapors from cooking shellfish. Shellfish allergy can develop at any age.
Even people who have eaten shellfish in the past can develop an allergy. Some people outgrow certain food allergies over time, but those with shellfish allergies usually have the allergy for the rest of their lives. When someone is allergic to shellfish, the body's immune system , which normally fights infections, overreacts to proteins in the shellfish.
Every time the person eats or, in some cases, handles or breathes in shellfish, the body thinks these proteins are harmful invaders and releases chemicals like histamine. This can cause symptoms such as:. Allergic reactions to shellfish can differ.
Sometimes the same person can react differently at different times. Some reactions can be very mild and involve only one system of the body, like hives on the skin. Other reactions can be more severe and involve more than one part of the body. Shellfish allergy can cause a severe reaction called anaphylaxis , even if a previous reaction was mild. Anaphylaxis might start with some of the same symptoms as a less severe reaction, but can quickly get worse.
The person may have trouble breathing or pass out. More than one part of the body might be involved. If it isn't treated, anaphylaxis can be life-threatening. If your child has a shellfish allergy or any kind of serious food allergy , the doctor will want him or her to carry an epinephrine auto-injector in case of an emergency. But iodine is not what triggers the reaction in people who are allergic to shellfish. The major allergen in shellfish is a muscle protein called tropomyosin and this is what is responsible for causing the allergic reaction.
If you have a shellfish allergy, you do not need to worry about cross-reactions with iodine or radiocontrast material which can contain iodine and is used in some radiographic medical procedures. Get to know this document, the cornerstone of personalized treatment for anyone with a food allergy. Prevalence of seafood allergy in the United States determined by a random telephone survey.
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