Types of seafood that can cause allergies

Allergies are caused by a reaction to specific proteins in foods. Allergic reactions can be caused by:

• fish (with a backbone), including salmon, cod, mackerel, sardines, herring, anchovies, tuna, trout, haddock, John Dory and eels
• shellfish (without a backbone), including crustaceans including prawns/shrimps, lobster, crab, crayfish, yabbies; and molluscs such as oysters, mussels, clams, octopus, squid, calamari, abalone, sea slugs.

Some people are allergic to fish only, others to shellfish only, and others to both groups.

If you are allergic to one type of seafood, you can’t predict whether you’ll be allergic to any other type of seafood. The only way to find out is through testing or experience.

Symptoms of seafood allergy

Most people who are allergic to seafood have mild symptoms such as:

• hives
• tingling in the mouth
• some swelling in the face, lips or eyes
• abdominal pain, vomiting or diarrhoea

But some people experience dangerous symptoms of anaphylaxis such as:

• difficulty breathing
• swelling of the tongue or tightness in the throat
• hoarse voice, wheezing or difficulty talking
• dizziness or collapsing due to a sudden drop in blood pressure

If you're experiencing any of these dangerous symptoms, you need urgent medical assistance. Call triple zero (000) or go straight to the emergency department of your nearest hospital.

If you are allergic to seafood, symptoms usually appear within minutes, but some people (especially those with an allergy to oysters, abalone, squid or prawns) may not experience symptoms until hours later. This sometimes happens after exercise.

Diagnosing seafood allergy

If you suspect you have an allergy, see your doctor, who can arrange appropriate skin or blood tests, and can help you understand what these mean. Your doctor can also prescribe an EpiPen for emergencies, if necessary.

Seafood allergies are complex. Even among fish, there are different groups of fish, and if you are allergic to one group of fish, you may be able to safely eat fish from other groups.

Allergy testing done under proper medical supervision is the only way to diagnose your specific seafood allergy.

Avoid testing methods advertised online or in print media. Tests that are considered unreliable include hair analysis, Alcat or Vega tests, kinesiology, iridology, reflexology, pulse and cytotoxic food tests.

How to avoid seafood

It's easy to avoid cooking or buying seafood, but ingredients made from seafood are added to many foods that you might not expect. Check the labels on processed or packaged foods. Canned fish or shellfish are obviously sources of seafood; other products and menu items to watch out for include:

• sauces such as oyster sauce and fish sauce (used in many Asian dishes)
• marinara sauce (used on pasta or pizza)
• fish paste
• fish stock
• prawn crackers and prawn crisps
• sushi
• Caesar salad (which may include anchovies)
• pizza (which may come with anchovies or other seafood)
• cooking oil previously used to cook fish
• fish or krill oil supplements

If you order a stir-fried dish or meat curry in a restaurant, for example, it may have been cooked with fish sauce. Make it very clear to waiters that you have a genuine allergy and your meal must not contain any seafood, fish sauce or oyster sauce.

Fish oil supplements are unlikely to cause an adverse reaction, but it’s probably safest to avoid them.

Glucosamine supplements (sometimes used for osteoarthritis) are made from the shells of crustaceans and are not suitable if you are allergic to shellfish.

Isinglass is an additive used to stop beer and wine from going cloudy. It is made from the bladders of fish, but food authorities consider it is so unlikely to cause an allergic reaction that legally it doesn’t need to be included on the label.

A small number of people are so sensitive to any kind of fish that they can have a reaction to the steam produced when fish is being cooked. This is more likely in children who also have asthma.