Allergies to shellfish and fish are more common in adults and adolescents than in young children. A recent study estimated that one in every 100 people has a seafood allergy. The types of seafood that can cause allergies include scaly fish and shellfish, including molluscs (such as oysters, mussels and squid) and crustaceans (such as prawns, crayfish and yabbies).
Symptoms of fish or shellfish allergies vary and range from mild reactions to a severe allergic reaction (anaphylaxis). The most common symptom is raised red bumps of skin (hives). Other symptoms include wheezing and trouble breathing, cramps, diarrhoea, nausea or vomiting. The best way to manage a shellfish or fish allergy is to avoid all food containing the species to which you are allergic.
Food allergies can be life threatening. If you, or a child in your care, have a severe allergic reaction (anaphylaxis), call triple zero (000) for an ambulance.
Symptoms of shellfish and fish allergies
Every person’s immune system is different, and shellfish and fish allergies can cause diverse symptoms, ranging from mild to severe. Many food allergies do not cause severe symptoms, but they can be life threatening in some people and should be taken seriously.
Fish and shellfish allergic reactions can occur after eating seafood, but you can also have symptoms after touching seafood or inhaling fumes from shellfish or fish while they are being cooked or processed in a factory.
Milder allergic symptoms that can occur before a severe allergic reaction include:
- raised red bumps of skin – hives (urticaria)
- swelling of the lips
- tingling of the throat and mouth
- itchy skin and rash
- runny nose
- tightening of the throat
- digestive symptoms – cramps, stomach pain, nausea or vomiting.
If you or a child in your care have experienced any of these symptoms after eating fish or shellfish, the risk of having a severe reaction after eating that food is greater than usual. Ask your doctor to refer you to a medical specialist, known as an allergist or clinical immunologist.
Keeping a record of your symptoms
Diagnosing an allergy can be difficult. If you think you or a child in your care may have an allergy, keeping a record of symptoms can help you and your doctor to understand what is causing them.
Your diary could include information about whether the symptoms occur:
- inside your home, outside or both
- for a short time or longer
- at night, during the day or when you wake up
- after you have had a particular food or drink
- after you have taken a particular medication, either prescription or over the counter from a pharmacy or supermarket
- after you have taken a herbal medicine.
Severe allergic reaction – anaphylaxis
A severe allergic reaction (anaphylaxis) is life threatening.
Symptoms of a severe allergic reaction include:
- difficult or noisy breathing
- swelling of the tongue
- swelling or tightness of the throat
- difficulty talking or a hoarse voice
- wheeze or persistent cough
- persistent dizziness or collapse
- paleness and floppiness in young children.
If you, or a child in your care, have a severe allergic reaction (anaphylaxis), call triple zero (000) for an ambulance. Do not stand or walk. Administer adrenaline (epinephrine) via autoinjector (EpiPen®), if available.
Causes of shellfish and fish allergies
For all allergies, the immune system reacts to specific allergy triggers (allergens). Your immune system produces antibodies that detect the allergen and cause inflammatory reactions and the release of a chemical called histamine. Histamine causes hives, hay fever and other allergic symptoms.
The specific molecule in shellfish or fish that triggers your allergy may be present in a range of foods, and you may then have an allergic reaction to all foods containing that molecule. Some people who are allergic to one type of fish may be allergic to another type of fish or they may have allergies to several crustaceans, such as prawn, crab and lobster. This is known as cross-reactivity. Speak to your doctor about cross-reactivity because it is difficult to predict.
The list of fish that can cause an allergic reaction is quite long and includes, but is not limited to:
The list of shellfish (including molluscs and crustaceans) that can cause allergic reactions includes, but is not limited to:
The Healthy Eating Advisory Service has more comprehensive lists of seafood that can cause an allergic reaction in some people. Visit your doctor for more information.
Diagnosis of shellfish and fish allergies
If you have allergic symptoms, visit your family doctor, who will ask some questions about your allergic reactions. You can also discuss your record of symptoms. To diagnose your allergy, your doctor may refer you to a specialist doctor known as an allergist or clinical immunologist.
Allergists can test for allergies using a number of methods depending on the type of potential allergy. To test for an allergy to shellfish or fish, the allergist may:
- do a skin prick test
- do a blood test
- ask you to temporarily avoid all shellfish or fish (elimination diet), then follow up with the introduction of the food back into your diet (food challenge) under strict medical supervision.
Unproven methods to test for allergies
A number of methods claim to test for allergies, but they have not been medically or scientifically proven. They can be costly and could lead to dangerous avoidance of certain foods. The Australasian Society of Clinical Immunology and Allergy (ASCIA), the organisation representing allergists in Australia, recommends that you do not use certain methods to have potential allergies tested. These methods include:
- cytotoxic food testing
- electrodermal testing
- hair analysis
- pulse testing
- Vega testing.
Always speak with your doctor if you are thinking of using a complementary medicine or therapy to test for allergies.
Treatment for shellfish and fish allergies
The only current treatment for food allergies is to avoid the food that causes your allergy. Even if you are careful, it is difficult to avoid all contact with a specific food. If you are at risk of a severe allergic reaction (and you have been prescribed an adrenaline (epinephrine) autoinjector (such as an EpiPen®), ASCIA recommends that you have an action plan for anaphylaxis.
If you are not at high risk and have not been prescribed an adrenaline autoinjector, ASCIA recommends that you have an ASCIA action plan for allergic reactions.
To help with food avoidance, people with food allergies need to become familiar and comfortable with reading food labels. ASCIA has fact sheets to help you understand how to read food labels and what to avoid if you have a shellfish or fish allergy.
Inaccurate diagnosis can lead to expensive and ineffective treatments, and unnecessary food avoidance that can lead to malnutrition and food aversion, especially in children. Always speak to your doctor about your food allergy diagnosis and treatment options.
Emergency treatment for severe allergic reactions
If you are at risk of a severe allergic reaction (anaphylaxis), carry an adrenaline autoinjector such as an EpiPen®, and a means of calling for medical assistance, such as a mobile telephone.
Emergency responses for a severe allergic reaction are:
- lay the person flat – do not allow them to stand or walk
- administer adrenaline with an autoinjector (such as an EpiPen®)
- always dial triple zero (000) to call an ambulance in a medical emergency.
If you are at risk of a severe allergic reaction, make sure you:
- have a severe allergic reaction action plan
- carry an adrenaline autoinjector (such as an EpiPen®) to treat a severe allergic reaction
- wear medical identification jewellery – this increases the likelihood that adrenaline will be administered in an emergency
- avoid medication (where possible) that may increase the severity of allergic reaction or complicate its treatment – such as beta blockers
- seek medical advice.
Where to get help
This page has been produced in consultation with and approved by:
Australasian Society of Clinical Immunology and Allergy (ASCIA)
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