Allergy to Fish: The Facts

If you know or suspect you are allergic to fish, it is important to see your GP as soon as possible. Some GPs have a clear understanding of allergy, but as allergy is a specialist subject your doctor may need to refer you to an allergy clinic. The results of skin prick tests and blood tests will help form a clear picture.

Your GP can locate an allergy clinic in your area by visiting the website of the British Society for Allergy and Clinical Immunology (www.bsaci.org).

In many cases, doctors cannot easily determine whether a food allergy is mild or severe. However, there will be certain clues. For example, the severity of the reaction you suffered and the amount of fish that caused it are important factors. If you have reacted to a very small amount, this suggests your allergy is probably severe. If you have asthma you may face a higher risk of severe reactions, especially if your asthma is poorly-controlled.

Allergy to fish often begins in childhood and is likely to be lifelong, but it can also begin in adulthood (Tsabouri et al., 2012).

People who are allergic to one type of fish have a high chance of reacting to others. For example, a study of nine common edible fish showed that cod, salmon, pollock, herring and wolf-fish share similar allergy-inducing proteins and are therefore very likely to cross-react (Torres Borrego et al., 2003). There is also a high chance of cross-contamination, for example in the fish market or on the supermarket counter where different types of fish are in close contact. For those reasons, people with fish allergy are normally advised to avoid all types of fish.

Shellfish (crustaceans and molluscs)

We are aware of no evidence to suggest that people who are allergic to fish are at significantly increased risk of allergy to shellfish such as crustaceans (which include shrimp, prawns, crayfish lobster and crab) and molluscs (which include squid, octopus, scallops and oysters). Uncommonly, people may suffer allergy to both groups (fish and shellfish), but this is more likely to be due to coincidence than cross-reactivity. If you suspect you are allergic to shellfish as well as fish, discuss this with your doctor.
People with allergies to crustaceans or molluscs are encouraged to read our separate Factsheet on shellfish allergy.

Pre-packaged foods

If you have a food allergy, always check ingredients. Under the law, all pre-packaged food sold within the UK must declare and highlight major allergens, including the presence of fish, crustaceans and molluscs, even if they appear in minute quantities.

Eating out

In restaurants, tell staff about your allergy. Even if you think you have chosen a safe dish still query the ingredients, including those in stocks and soups. Remember that everyday meals such as shepherd’s pie might contain fish if Worcestershire sauce (which contains anchovies) is an ingredient.

Check to find out if there is any risk of cross-contamination. Find out what your food is fried in and whether the oil has been used for anything else. For example, your chips could be fried in the same oil as fish (Lehrer et al., 2007).

Caterers are governed by strict laws. When you eat out or buy from a takeaway, the food business will be required to provide information on major allergenic ingredients. This information can be provided in writing and/or by word of mouth. If information is provided by word of mouth, the food business will need to ensure there is written signage clearly visible to indicate that you can obtain allergen information from a member of staff. Systems must be in place to ensure the information you receive is accurate. These rules also apply to food sold loose – for example on deli counters or in-store bakeries.

Caesar salad and Caesar dressings normally contain anchovies. They might not be easily noticed.

Worcestershire Sauce contains anchovies. Products labelled “Worcester Sauce” may or may not contain anchovies so it is important to read the label.

Fish sauce is commonly served here in the UK and also elsewhere in the world – notably in the Far East.

Scampi the name given to large shellfish fried in breadcrumbs but white fish can be used instead. Pre-packed scampi should make the ingredients clear on the label.

Examples of foreign dishes to watch out for:

• Kedgeree
• Paella
• Bouillabaisse
• Gumbo
• Jambalaya
• Fritto Misto
• Etouffee

If you see any of these on sale, check with staff to find out exactly what ingredients are used.

Whenever the term ‘seafood’ is used, for example on a menu, check to find out what this means as some people believe it includes only shellfish.

Personal care products

Food ingredients such as oils can turn up in non-food products including cosmetics, toiletries, medicines and bath and massage oils. As an example, our medical advisers know of a case where an eye shadow that contained fish scales (to make the wearer’s eyelids glitter) caused severe facial dermatitis in a teenage girl with a known fish allergy. We advise that if you react to any product in this way, stop using it, try to find out the ingredients and consult your doctor.

Omega 3

There is no definitive research showing whether Omega 3, when derived from fish, will trigger reactions in people with fish allergy. We advise people with fish allergy to avoid Omega 3 unless they know it has been derived from a non-fish source.

Fish gelatin

Fish gelatin is an alternative to beef or pork gelatin. It is extracted from the skin and bones of several fishes, such as cod, pollock, salmon or tuna. A 2008 study showed that fish gelatin can be a trigger for severe allergic reactions (Kuehn et al., 2009). Anyone who is fish-allergic should check food labels to see whether the source of gelatin is fish or not. Products that may have fish gelatin as an ingredient include marshmallow and nougat.

Some people who suspect they are allergic to fish may in fact suffer from one of these conditions:

• Anisakis simplex (also known as the herring worm) is a common parasite present in many marine fish and shellfish (Olivares et al., 2015). Not only can it cause human infection, it can also cause allergic reactions in a very small minority of people. People reacting to anisakis may think they have fish or shellfish allergy. Anyone reacting to a particular shellfish or fish that they have previously eaten with no problem should consider the possibility that the herring worm was responsible and seek medical advice.
• Histamine poisoning: Histamine can sometimes be present in spoiled fish (especially tuna and mackerel) and can cause a condition not unlike allergy called scombroid poisoning (Attaran & Probst, 2002). Unlike an allergy, this would often affect everyone who ate the offending food, although some people might be more susceptible than others.

Your doctor should be able to confirm whether you have an allergy or whether one of the above conditions caused your symptoms.