Food Allergies and Intolerances - Symptoms and Diagnosis

Food allergies in young children are more common than in adults, but it’s possible to develop a food allergy as an adult — even if you’ve never had one as a child.

Food and the immune system

If you have an allergy to a particular food, your body’s immune system mistakenly identifies this food as harmful. On first encountering a problem food, your immune system produces specific proteins to ‘fight’ the problem food. These proteins are called antibodies. Although this may not cause any immediate symptoms, the antibodies ‘sensitise’ your immune cells. Each time you are exposed to this problem food again, your immune system can have a ‘bigger’ reaction. Over time, this can lead to you experiencing symptoms of an allergic reaction.

General symptoms

Some food allergies result in immediate, severe and even life-threatening symptoms, whereas others cause symptoms which may take longer to develop.

Some of the symptoms you may get include:

• itching and/or swelling of your lips, mouth, tongue and throat
• constriction or tightening of your throat and airways
• wheezing or shortness of breath
• coughing
• runny nose
• sore, red and itchy eyes
• skin reactions (eg swelling and itching, hives, eczema and flushing)
• diarrhoea, feeling nauseous, vomiting and bloating of the stomach.

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

• extreme tiredness
• arthritis or sore joints.

It’s important to note that many of these symptoms can also be caused by problems other than a food allergy, so you should visit your GP for advice if you experience any of these symptoms.

Anaphylaxis — a complication of a severe food allergy

Although it can be uncommon, in some cases, people develop life-threatening reactions to certain foods. This can appear as a severe, whole-body allergic reaction called anaphylaxis, or anaphylactic shock.

Symptoms of anaphylaxis can include dizziness, a rapid pulse, a rapid drop in blood pressure and extreme swelling of the airways and throat, making it difficult to breathe. Anaphylaxis can occur very quickly and can result in loss of consciousness or even death if left untreated. If someone around you has any of these symptoms, you should get them medical help immediately.

Common triggers

It’s not clear exactly why or how food allergies are caused, but a number of foods are known to be common triggers. Problem foods include peanuts, tree nuts (including macadamia and Brazil nuts, pecans, cashews, pistachios, almonds, hazelnuts and walnuts), fish and shellfish, cow’s milk, eggs, soya and wheat. However, almost any food can cause an allergic reaction.

If you have an allergy to one food, you may also react to other related foods. For instance, if you’re allergic to prawns, other shellfish may also affect you. Be cautious when encountering food items which belong to the same class of problem foods as the food you are allergic to.

Diagnosis

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

To reach a diagnosis, your doctor will ask you about your symptoms and examine you. They may also ask you about your medical history. Some examples of questions you might be asked are listed below. Try and take note of your answers to these questions if you are experiencing symptoms associated with food allergies.

• Do you always get this reaction to the food? How much did you eat?
• How quickly did the reaction start?
• Have you tried any treatment (eg antihistamines) and did it work?
• 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 allergies?

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

If you are not diagnosed with a food allergy but your symptoms continue, make sure to check back with your doctor. This could be an indication of another condition.

Elimination and challenge diets

An allergy specialist or your doctor may ask you to remove the suspected problem food from your diet. If your symptoms improve, a preliminary diagnosis can often be made.

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

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

Skin prick tests

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

You can sometimes 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 conjunction with other tests.

Again, due to the risk of severe allergic reactions, particularly if you have had such reactions in the past, these tests are generally carried out in hospitals or allergy clinics under strict medical supervision.

Blood tests

Blood tests are useful if you can’t have a skin test due to a severe food allergy that puts you at risk of anaphylaxis or if you have extensive eczema or dermatitis.

The RAST (RadioAllergoSorbent) test measures levels of food-specific antibodies in your blood as a reflection of how sensitive your body is to that food. However, 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). So it’s often used in combination with other tests to confirm a diagnosis.

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 Vega testing, hair testing, electro-acupuncture, and various kinds of blood tests.

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 worrying false positive results, or false reassurance with false negative results.

For more information on allergy tests, including unproven allergy tests, see the Australasian Society of Clinical Immunology and Allergy (ASCIA) website.

Managing food allergies

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

The only treatment for a food allergy is to not eat and avoid the problem food. An accredited practising dietitian can help you identify and remove a problem food from your diet and if required, 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 ask about 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 or pharmacist. And always read any patient information leaflet available for your medicine. If you have any questions, ask your pharmacist or doctor for help.

Emergency treatment

Even if you read menus and ingredient lists carefully, it’s possible to eat a problem food by accident. For some people, a tiny amount of a problem food can trigger a severe and sometimes life-threatening reaction. People with severe food allergies who are at risk of anaphylaxis need to take precautions.

• Make sure your doctor or pharmacist counsels you on how to manage in the event of an allergic reaction.
• Wear a medical alert bracelet or carry a card that gives details about your allergy.
• Carry a pre-loaded adrenaline syringe (eg EpiPen). You and those around you, such as friends and family, must know how to use it in case you have an anaphylactic reaction. Check regularly to make sure that the syringe is in full working order and within its expiry date. If you need to 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 and quickly in an emergency.

Further information

Australasian Society of Clinical Immunology and Allergy (ASCIA). http://www.allergy.org.au

Sources

Australasian Society of Clinical Immunology and Allergy (ASCIA). Food allergy. [online] Balgowlah, NSW: ASCIA; c2010 [updated Jan 2010, accessed 2 Aug 2010] Available from: http://www.allergy.org.au/content/view/167/140/

Australasian Society of Clinical Immunology and Allergy (ASCIA). Management of food allergy. [online] Balgowlah, NSW: ASCIA; c2010 [updated Jan 2010, accessed 2 Aug 2010] Available from: http://www.allergy.org.au/

Food Standards Australia New Zealand. Information for allergy sufferers. [online] c1991-2010 [accessed 2 Aug 2010] Available from: http://www.foodstandards.gov.au/

Chang HJ, Burke AE, Glass RM. Food allergies. Journal of the American Medical Association. [online] 2010. 303(18): 1876. [accessed 2 Aug 2010] Available from: http://jama.ama-assn.org/cgi/content/full/303/18/1876

The Royal College of Pathologists. Allergy and allergy tests – A guide for patients and relatives. [online] London: Royal College of Pathologists; 2002, revised 2005. p. 5-7. [accessed 2 Aug 2010] Available from: http://www.rcpath.org/

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