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Food allergy

Published by Bupa's health information team, September 2008.

This factsheet is for people who are concerned about food allergies, or who would like information about them.

If you have a food allergy, your body's immune system mistakes particular foods, for example eggs or nuts, as harmful. An allergic reaction to food can cause a range of symptoms.

• About food allergies
• Symptoms of food allergy
• Complications of food allergy
• Causes of food allergy
• Diagnosis
• Treatment of food allergy
• Questions and answers
• Related topics
• Related Bupa products and services
• Further information
• Sources

About food allergies

Around one in five people in the UK think that they have a food allergy - however, food allergy is estimated to affect only around one in 70 adults. Food allergy is sometimes confused with food intolerance or food poisoning. These can make you feel ill but they aren't usually harmful in the same way that a true food allergy might be.

Food allergies in young children are more common than in adults, but many children outgrow them by school age. It's possible to develop a food allergy as an adult, even if you never had allergies as a child.

Food and the immune system

If you have a food allergy, your body mistakes certain foods as harmful, and produces antibodies. This is known as sensitisation and may not cause symptoms. However, the next time you eat the food, the antibodies are ready to react with it. This causes the body to release chemicals, which lead to a range of physical symptoms known as an allergic reaction.

Symptoms of food allergy

Some food allergies result in immediate, severe and even life-threatening symptoms (such as severe peanut allergy), whereas others cause symptoms which may take longer to develop (for example, gluten allergy, also known as coeliac disease).

You may get some or all of the following symptoms:

• itching and/or swelling of your lips, mouth, tongue and throat
• skin reactions (eg swelling and itching, eczema and flushing)
• diarrhoea, feeling sick, vomiting and bloating
• coughing
• wheezing or shortness of breath
• runny nose
• sore, red and itchy eyes

You may also have symptoms that affect your whole body, such as:

• extreme tiredness
• arthritis

These symptoms can be caused by problems other than food allergy, so you should visit your GP for advice.

Complications of food allergy

Sometimes people have an allergic reaction to food that is triggered by exercise. Not eating for a couple of hours before exercise may prevent this problem.

Some people develop a severe, whole-body allergic reaction called anaphylaxis, or anaphylactic shock; a rare but potentially fatal allergic reaction. Symptoms can include dizziness, a rapid pulse, a rapid drop in blood pressure and swelling of the airways and throat, making it difficult to breathe. This could result in loss of consciousness if left untreated.

Causes of food allergy

Problem foods include peanuts, tree nuts (including macadamia and Brazil nuts, pecans, cashews, pistachios, almonds, hazelnuts and walnuts), fish and shellfish, cows' milk, eggs, soya and wheat.

If you have one food allergy, you may also react to other foods (cross-reactivity). For instance, if you're allergic to prawns, other shellfish may also affect you. People with hay fever or an allergy to latex may also have a cross-reaction to certain foods.

Diagnosis

The diagnosis of a food allergy isn't always straightforward. Many food allergy symptoms can also be caused by a number of other conditions and it may take some time before the problem food is identified and your doctor can confirm that you have an allergy.

Your GP will ask you about your symptoms and examine you. He or she may also ask you about your medical history. Some examples of questions you might be asked are listed below.

• How quickly did the reaction start?
• Did you take treatment (eg antihistamines) and did it work?
• Do you always get this reaction to the food? How much did you eat?
• Did anybody else eating the food get ill?
• How was the food cooked and stored?
• Do you have a family history of eczema, asthma, hay fever or food allergy?

If an allergy seems likely, your GP may refer you for testing at a specialist allergy clinic.

Elimination and challenge diets

An allergy specialist may ask you to remove the suspected allergy food from your diet and replace it with another food. If your symptoms improve, a diagnosis can usually be made.

To confirm this diagnosis, your doctor may then ask you to re-introduce the food back into your diet. If you have had severe allergy symptoms in the past, this will be done under medical supervision in hospital.

It's important, particularly for children, that you don't cut out food groups without first getting medical advice, as you could risk missing out on essential nutrients.

Skin prick tests

In a skin prick test, an extract of the suspect food is put on a small patch of skin, usually on your forearm or back, and a very small, fine scratch is made. If redness and swelling develops around the scratch, the test is positive for that food.

However, you can develop a positive reaction to this type of test without having allergic symptoms when you eat the food. These 'false positives' mean that the test isn't always completely reliable, so it's usually used in combination with other tests.

Again, there is a small risk if you have had severe allergic reactions in the past and therefore these tests are always carried out in hospital.

Blood tests

Blood tests are useful if you have a severe food allergy and are at risk of anaphylaxis or if you have extensive eczema or dermatitis and can't have a skin test. The RAST (radioallergeosorbent) test measures levels of food-specific antibodies in your blood. This test can result in false positive results (as in skin prick tests), or in false negative results (when your body produces antibodies but they aren't circulated in the blood).

Unproven allergy tests

Numerous tests that claim to detect allergies are available by mail order or online, through health food shops, sports centres and complementary practitioners. These include hair testing, electro-acupuncture, and various kinds of blood test.

There is no scientific evidence to prove that these tests have any value in diagnosing or managing food allergy. They can be expensive, and may give a worrying false positive result, or false reassurance. For this reason, the Royal College of Pathologists recommends that you don't use them.

Treatment of food allergy

Managing food allergies

Some people outgrow their food allergies, especially children. However, this is unlikely with allergies to nuts and fish.

The only treatment for food allergy is not to eat the problem food. A registered dietitian can help you identify and remove a problem food from your diet and replace it with alternatives, to make sure you don't miss out on essential nutrients. Your dietitian can also explain what you need to look for on food labels and when eating out. Symptoms of mild food allergies, such as a rash or runny nose, may be treated with antihistamines. However, it's important that you only take medicines for your allergy on the advice of your doctor. Always read the patient information leaflet that comes with your medicine and if you have any questions, ask your pharmacist for advice.

Emergency treatment

People with severe food allergies who are at risk of anaphylaxis need to take certain precautions. Despite reading menus and ingredients lists carefully, it's easy to eat a problem food by accident. Even a tiny amount of a problem food can trigger a severe reaction.

• Make sure that your doctor teaches you how to cope if you have an allergic reaction.
• Wear a bracelet or carry a card that gives details about your allergy.
• Carry a pre-loaded adrenaline syringe (eg EpiPen). You must know how to use it in case you have an anaphylactic reaction. Check regularly to make sure that it's in full working order and within its expiry date. If you use this, you must always seek medical attention immediately afterwards.
• Let your family, friends and work colleagues know of your allergy, and how they can help in the event of an emergency.
• If your child has a severe allergy, you must make sure that all their carers and teachers have the knowledge and ability to react correctly in an emergency.

Related topics

• Colonoscopy
• Egg allergy
• Food hygiene
• Gastroenteritis in adults
• Gastroenteritis in children
• Gastroscopy
• Nut allergy

Further information

• Allergy UK
  01322 619 898
  www.allergyuk.org
• Food Standards Agency
  www.eatwell.gov.uk
• Royal College of Pathologists
  www.rcpath.org

Sources

• Adverse reactions to foods. British Nutrition Foundation. www.nutrition.org.uk, accessed 22 April 2008
• Adverse reactions to food and food ingredients. Committee on toxicity of chemicals in food, consumer products and the environment, 2002. www.food.gov.uk
• Eat well, be well - Allergic reactions to food. Food Standards Agency. www.eatwell.gov.uk, accessed 22 April 2008
• Bischoff SC. Food allergies. Curr Gastroenterol Rep 2006; 8:374-382. www.current-reports.com
• A review of services for allergy - the epidemiology, demand for and provision of treatment and effectiveness of clinical interventions. Section 3.12. Department of Health, 20 May 2006. www.dh.gov.uk
• Allergy and allergy tests - A guide for patients and relatives. Section 13, 15. Royal College of Pathologists, revised 2005. www.rcpath.org, accessed 22 April 2008
• Simon C, Everitt H, Kendrick T. Oxford Handbook of General Practice. 2nd ed. Oxford: Oxford University Press, 2007:539
• Dietitian. NHS careers. www.nhscareers.nhs.uk, accessed 22 April 2008
• Food allergy and food intolerance tips. Allergy UK. www.allergyuk.org, accessed 30 April 2008

This information was published by Bupa's health information team and is based on reputable sources of medical evidence. It has been peer reviewed by Bupa doctors. The content is intended for general information only and does not replace the need for personal advice from a qualified health professional.

Publication date: September 2008