Causes and Symptoms of A Shellfish Allergy
Food allergies are the result of a fault in the body’s immune system that incorrectly identifies certain foods as invaders to the body. The noticeable symptoms of a food allergy are the results of the immune system trying to rid the body of the invading food. A crustacean allergy is a so-called IgE-mediated food allergy with IgE (Immunoglobulin E) being the allergy antibody.
One of the more common food allergies, affecting around 2 per cent of the population is shellfish allergy. There are two groups into which you can categorize shellfish, there are the crustacean such as shrimp, crab and lobster, and then there are the mollusks such as oysters, squid, octopus, scallops and mussels.
Once a shellfish allergy has been diagnosed the best way to deal with it is complete avoidance, however many people who are allergic to shellfish in the crustacean group may be able to tolerate mollusks and vice versa.
Symptoms of A Shellfish Allergy
The severity of reactions to a shellfish allergy can range widely from the mild to extremely severe. The symptoms of shellfish allergies can become apparent within minutes of consuming it, but it can also take a few hours before any reaction becomes apparent. Here are some of the symptoms to look out for.
- Hives, itching or eczema.
- Swelling that affects the lips, face, tongue and throat. The swelling can become severe enough to become life threatening.
- Difficulty in breathing
- Wheezing or shortness of breath.
- Nausea or vomiting
- Abdominal pains.
It is rare that an allergic reaction to shellfish can result in life-threatening anaphylaxis, but it is a symptom that is possible. Anaphylaxis results in breathing difficulties and should be treated as an emergency, getting the patient to the hospital emergency room as soon as possible.
What Is It About Shellfish That Causes An Allergic Reaction
As with other food allergies, the auto-immune system in your body malfunctions and identifies the shellfish protein as harmful to the body. Antibodies are triggered in order to neutralize the protein and histamine in the body are released which are a factor in the allergic reaction symptoms we experience.
People who are allergic to shellfish must also be on guard for products that contain the shellfish proteins to which their bodies react. Some dietary supplements contain shells from crustaceans and although it is indicated by studies that it is unlikely that the allergies will be triggered by the crustacean shells, those who are concerned should avoid taking glucosamine.
Another supplement that potentially contains extracts from shellfish is Omega-3 supplements. These are often made from seafood, most often fish, but it is recommended that you check the label for the ingredients before taking them.
Molluscs - Oyster Allergy Symptoms
An allergy to oysters, as opposed to other kinds of shellfish such as crustaceans, is not as common. The oyster allergy symptoms are very similar to other food allergies with the symptoms usually mild such as oral allergy syndrome. This means conditions ranging from an itching of the lips, throat and larynx to swelling of the lips, tongue, throat and palate. It can become more dangerous with a more commonly reported symptom being urticaria, or hives. However anaphylactic shock can occur after consumption of oysters.
Oysters are bivalve molluscs and so if a person is allergic to other bivalves such as clams, mussels and scallops then there is a good chance that they should avoid other molluscs too. This goes for snails, limpets, cuttlefish, octopus and squid too.
The allergic symptoms after eating oysters usually begin to occur within 90 minutes after eating them, although it’s not unusual that the symptoms present themselves later.
When talking about an oyster allergy we are usually talking about the ingestion of oysters, however symptoms have also been reported after handling them or even after inhaling the steam while cooking.
Sometimes the use of a crustacean in a dish may not be immediately obvious yet the effects will be just as severe. Take squid ink as an example. Squid ink may be used as a food dye, as with its use to color pasta. Similarly the use of cuttlefish ink has the potential to cause the same reaction, being part of the mollusc family.
If is very possible that any dish that has been created with a fish stock base can contain traces of shellfish of some kind or another. Whether the allergy is to shellfish specifically or to molluscs, there is the risk of causing a reaction.
For many people the wisest course of action is to avoid seafood restaurants or dishes that have been prepared by someone who is unaware of your allergy.
Protecting Against Shellfish
There is now a requirement in the US under the Food Allergen Labeling and Consumer Protection Act (FALCPA) that all packaged foods containing shellfish must list the specific shellfish on the label.
Remember that ingredients can change over time and just because a certain type of shellfish wasn’t used by a brand in the past doesn’t mean that it will continue to be absent. Check the label every time you shop.
List of Shellfish To Avoid
According to the FALCPA mollusks are not considered to be major allergens and so will not be specifically noted on product labels. Therefore it is important to be aware of the following mollusks:
- Sea cucumber
- Sea urchin
- Squid (calamari)
Who Might Be Susceptible To A Shellfish Allergy?
There has been some research that indicates that if your parents or someone in your family suffers from shellfish allergy, the chances are high that you may be as well. To avoid inadvertently eating shellfish and suffering either a mild or severe allergic reaction, it is advisable to go to the doctor to get tested.
It appears that women are more likely to have a shellfish allergy than men which could indicate a difference in the immune systems between the sexes. This is merely speculation with no definitive research having been performed yet.
The Likelihood Of Cross-Reactions
There are figures available that suggest that someone who is allergic to one kind of crustacean will have a 75% chance of being allergic to another. This is known as cross-reactivity and the cross-reaction is also valid between crustacean and mollusc allergies too.
Interestingly the cross-reactivity molecules responsible for allergies in crustaceans are also responsible for dust-mite and cockroach allergies.
A Shellfish Allergy Test
The most effective way to find out the extent of your shellfish allergy is to have your doctor perform either a skin test or a blood test. With a skin test your skin is pricked and is exposed to small amounts of the protein found in shellfish and the reaction is assessed in whether a small bump (known as a hive) appears in the skin. A blood test is also referred to as an allergen specific IgE antibody test by measuring the antibodies in the bloodstream as a response to shellfish proteins. It is a test of your body’s immune system and the blood sample is sent to a medical laboratory for testing.
Shellfish Allergy May Be Even More Widespread
There are a number of factors surrounding shellfish allergies that suggest that it could be more widespread than the number indicate. The nature of the various types of shellfish and some folk’s aversion to it could mean that there are people who are allergic to it but are too repulsed by the thought of eating an oyster to find out. The look and smell of shellfish causes many to keep their distance and, who knows, perhaps that is protecting them from coming in contact with an allergen.
Another factor that could be skewing the figures is that the majority of shellfish is quite expensive and so a fair chunk of the community simply can’t afford to buy it.
If you experience any strange feeling after eating any kind of shellfish it is highly advisable that you consult a doctor and get yourself tested for shellfish allergy.
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