The Australasian Society of Clinical Immunology and Allergy

Food allergy occurs in around 1 in 20 children and in about 1 in 100 adults. The majority of food allergies in children are not severe, and will disappear with time. The most common triggers are hens egg, cows milk, peanut and tree nuts, with less common triggers of seafood, sesame Soy, fish and wheat, with peanut, tree nuts, seeds and seafood being the major triggers for life-long allergies. Some food allergies can be severe, causing life-threatening reactions known as anaphylaxis.

Many people think they are allergic to food, but many are wrong...

The term "allergy" is often misused to describe annoying (but ultimately harmless) symptoms such as headaches after overindulging in chocolate or red wine, or bloating after drinking a milkshake. While these reactions are not allergic, the result is a widespread impression that all food reactions are trivial. Unfortunately, when severe food allergic reactions do occur, they are frightening for patients and those involved in their care, and may be life-threatening.

What is allergy?

Underneath the lining of the skin, gut, lungs, nose and eyes are mast cells. These are designed to kill worms and parasites. Mast cells are like bean bags filled with irritant chemicals including histamine. Mast cells are armed with proteins called IgE antibodies, which act to detect allergens in the local environment. A person allergic to peanut, for example, will have IgE antibodies capable of recognizing the shape of peanut protein (the allergen), in much the same way that a lock "recognizes" the shape of a key. When this happens, mast cells are triggered to dump their contents (such as histamine) into the tissues, causing an allergic reaction.

Symptoms of food allergy are usually obvious

Symptoms of food allergy typically include hives, swelling around the mouth, and vomiting, usually within 30 minutes of eating a food. Other symptoms include a runny or blocked nose, stomach pains, or diarrhoea.

More serious symptoms (known as "anaphylaxis") involve the breathing and circulatory systems (called anaphylaxis) and may include any of the following: noisy breathing, difficulty breathing, hoarse voice, dizziness, or in children becoming limp and floppy. 

Sometimes food allergy may be less obvious

Less common manifestations of food allergy include infantile colic, reflux of stomach contents, eczema, chronic diarrhoea and failure to thrive in infants.

Food allergy can sometimes be dangerous

Anaphylaxis is the most severe form of allergic reaction. It results in potentially life-threatening symptoms such as difficulty breathing, noisy breathing, hoarse voice, dizziness, a pale/floppy infant, or a drop in blood pressure (shock). Deaths from food allergy are rare in Australia. The most common foods causing life-threatening anaphylaxis are peanuts, tree nuts and shellfish.

How common is food allergy?

Studies have shown that food allergy affects between 2.3 and 3% of children aged 0-6 years. This is less common than complaints about adverse food reactions, as these often food intolerance, toxic reactions, food poisoning, enzyme deficiencies or irritation from skin contact with certain foods, being mistaken for food allergy.

Is food allergy increasing?

Hospital admissions for serious allergic reactions (anaphylaxis) have doubled over the last decade in Australia, USA and UK. In Australia, admissions for anaphylaxis due to food allergy in children aged 0-4 years are even higher, having increased five-fold over the same period.   Studies from the UK and USA  have shown that peanut allergy in children increased from 0.5 to 1.5% between 1989 and 1994-6 and 0.6 % to 1.2 % between 1997 and 2002. These data taken together with longer allergy clinic waiting lists in Australia and New Zealand, are consistent with a recent marked increase in the prevalence of food allergy, that closely follows the previously described increases in eczema and hay fever prevalence, although the prevalence of asthma seems to have stabilised in recent years.

Why the rise in food allergy?

We currently do not have clear information as to why food allergy seems to have increased so rapidly in recent years, particularly in young children. Proposed explanations (which have not yet been proven in studies) include:

• Hygiene Hypothesis (which proposes that less exposure to infections in early childhood is associated with an increased risk of allergy)
• Mother's diet during pregnancy or breast-feeding
• Early versus delayed introduction of allergenic foods such as egg, peanut or tree nuts
• Methods of food processing (such as roasted versus boiled peanuts)
• Development of allergy to food by skin exposure through the use of nut-oil based moisturisers.

This area requires additional research studies, several of which are underway.  

Allergies to cow's milk, soy, eggs, peanuts and tree nuts are the most common in children.

Food is the most common cause of allergy in young children, particularly cow's milk, egg, peanuts, tree nuts (most commonly cashew nut), sesame seed, soy and wheat. Peanuts, tree nuts, shellfish, fish, seeds and egg are the most common food allergens in older children and adults, although other triggers such as herbal medicines, fruit and vegetables have been described. Nevertheless, almost any food can cause allergic reactions in older patients.

When does food allergy develop?

Food allergy can develop at any age, but is most common in young children aged less than 5 years. Even young babies can develop symptoms of food allergy.

Identifying the cause

Your doctor will normally ask a series of questions that may help to narrow down the list of likely causes such as foods or medicines consumed that day, or exposure to stinging insects. This approach will also help to exclude conditions that can sometimes be confused with food allergy and anaphylaxis. Skin or blood (RAST/ ImmunoCap/ Immunlite) allergy testing helps confirm or exclude potential triggers. Sometimes a temporary "elimination diet" under close medical and dietetic supervision will be needed, followed by challenges to identify the cause. Long term unsupervised restricted diets should not be undertaken, as this can lead to malnutrition. While the results of allergy testing are a guide to whether the person is allergic, they do not provide a reliable guide to whether the reaction will be mild or severe.

Food allergy does not usually run in families

Most of the time, children with food allergy do not have parents with food allergy. If a family has one child with food allergy, however, their brothers and sisters are at a slightly higher risk of having food allergy themselves, although that risk is still relatively low. Some parents want to have their other children "screened" for food allergy. If the test is negative, that may be reassuring, but does not mean that the other child will never develop an allergy in the future. If their screening test is positive, however, it is not always clear whether it definitely represents allergy. In this situation, a food challenge may be required to settle the question definitively.  

A positive allergy test is not the same as being food allergic

It is important to know that a positive skin or blood allergy tests means that the body's immune system has produced a response to a food, but sometimes these are "false positives". In other words, the test may be positive yet the person can actually eat the food without a problem. For that reason, it is important to eventually confirm the significance of a positive allergy test (in some circumstances) with a deliberate supervised challenge. In a child with a positive test of uncertain meaning, this is often done around school-entry age under medical supervision. Interpretation of test results (and whether challenge should be undertaken) should be discussed with your doctor.

Unorthodox so-called "allergy tests" are unproven

There are several methods of unorthodox "tests" for food allergy. Examples include cytotoxic food testing, Vega testing, kinesiology, iridology, pulse testing, Alcat testing and Rinkel's intradermal skin testing and IgG food antibody testing. These have no scientific basis, are unreliable and have no useful role in the assessment of allergy.  These techniques have not been shown to be reliable or reproducible when subjected to formal study. ASCIA advises against the use of these tests for diagnosis or to guide medical treatment. No Medicare rebate is available in Australia for these tests, and their use is not supported in New Zealand. Adverse consequences may also arise from unorthodox testing and treatments. Treatment based on inaccurate, false positive or clinically irrelevant results is not only misleading, but can lead to ineffective and at times expensive treatments, and delay more effective therapy.  Sometimes harmful therapy may result, such as unnecessary dietary avoidance and risk of malnutrition, particularly in children

Most people grow out of their food allergy

Most children allergic to cow's milk, soy, wheat and egg will be able to tolerate it by the time they reach school age, often before. By contrast, allergic reactions to peanut, tree nuts, seeds and seafood persist in the majority (~ 75%) of children affected. When food allergy develops for the first time in adults, it usually persists.

Reactions may be mild or severe, and may be influenced by a number of factors:

• The severity of the allergy
• The amount eaten
• The form of the food (liquid may sometimes be absorbed faster)
• Whether it is eaten on its own or mixed in with other foods
• Exercise around the same time as the meal may worsen severity.
• Cooked food is sometimes better tolerated
• The presence or absence of asthma

Can food allergies be prevented?

There are few studies of allergy prevention, and even fewer examining food allergies. Therefore even if you follow the following advice, this may not result in prevention of allergy.

• Wherever possible, breastfeed your child for at least the first 4-6 months if possible. If breastfeeding isn't possible, use a partially hydrolysed formula (unless a cows milk allergy is already established)
• Don't smoke during pregnancy
• Avoid exposure to tobacco smoke in the home
• There is no evidence that restricting a mother's diet during pregnancy or during breastfeeding reduces the risk of developing food allergy. Such restrictions can adversely affect growth in babies and is not recommended.
• If you suspect allergy to a specific food, seek medical advice before introducing it.
• When breastfeeding isn't possible, a suitable formula should be given up until 12 months to ensure adequate nutrition. In children with confirmed cow's milk and soy allergy, appropriate formula is available on prescription from your doctor.

Living with your food allergy

The principles of managing food allergy are to:

• Identify and avoid the cause (if possible)
• Recognize the early symptoms of an allergic reaction
• Know what to do if it happens again

Research into food allergy is ongoing

The increased frequency of food allergy is driving research into areas such as trying to find out why it has become more common, and how to treat it. Current areas of research include immunotherapy/desensitization ("allergy vaccines") to "switch off" the allergy once it has developed. Initial results are encouraging but not yet ready for routine  clinical use.

Action Plans are essential

The average food allergic person will have an accidental exposure every few years, even when they are very careful to avoid their trigger. The difficulties of avoiding some foods completely make it essential to make back-up Action Plans, and Anaphylaxis Action Plans where EpiPen has been recommended. These are discussed in further details in the article Management of Food Allergy.

Food allergy can be effectively managed

The good news is that in concert with a trained allergist and a network of supportive contacts, people with food allergy can learn to live with their condition. The knowledge that EpiPen (an automatic device for administering adrenaline) is available offers reassurance, but is not a substitute for strategies to minimize the risk of exposure. Research continues to explore new ways of more effectively treating this condition. Anaphylaxis Australia (www.allergyfacts.org.au) and Allergy New Zealand (www.allergy.org.nz) offer valuable updates and tips for dealing positively with food allergies.

Further information on food allergy and anaphylaxis is provided in accompanying articles in this series and on the ASCIA website http://www.allergy.org.au/

Reference

Further Information:

The Australasian Society of Clinical Immunology and Allergy (ASCIA) is the peak professional body of Clinical Immunologists and Allergists in Australia and New Zealand.

For further information on allergy, asthma or immune diseases visit www.allergy.org.au/ - the website of ASCIA.

Disclaimer:

The content of this brochure has been reviewed by ASCIA members, represents the available published literature at the time of review, is not influenced by its sponsors and is not intended to replace professional medical advice. Any questions regarding a medical diagnosis or treatment should be directed to a medical practitioner.

Contact details:

PO Box 450 Balgowlah NSW 2093

© ASCIA 2008

Content last updated July 2008