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Food allergies occur 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. However, peanuts, tree nuts, seeds and seafood tend to cause life-long allergies. Some food allergies can be severe, causing life-threatening reactions known as anaphylaxis.
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 a milkshake. The result is a widespread impression (in both the lay and medical community) that all food allergies are trivial. Unfortunately, when severe reactions do occur, they are frightening for patients and those involved in their care, and may be life-threatening.
Underneath the lining of the skin, gut, lungs, nose and eyes are mast cells which are designed to kill worms and parasites. Mast cells are like bean bags filled with irritant chemicals including histamine and are armed with proteins called IgE antibodies, which act as remote sensors in the local environment. For example, someone allergic to peanuts will have IgE antibodies capable of recognising the shape of peanut proteins (the allergen), in much the same way that a lock "recognises" 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.
Many allergic reactions are mild and limited to localised hives or swelling. The most serious symptoms are breathing difficulties or a drop in blood pressure (shock), either of which can be life threatening. Anaphylaxis is the most severe form of allergic reaction. Other symptoms include swelling of the face or throat, dizziness, difficulty thinking, an intense sense of fear, a runny or blocked nose, tightness in the chest, wheezing, stomach pains, vomiting or diarrhoea.
Less common manifestations of food allergies include infantile colic, reflux of stomach contents, eczema, chronic diarrhoea and failure to thrive.
Anaphylaxis is the most severe form of allergic reaction. It results in potentially life-threatening symptoms such as difficulty breathing, hives, stomach upsets or a drop in blood pressure (shock). Deaths from food allergies are rare in Australia. The most common foods causing life-threatening anaphylaxis are peanuts, tree nuts and shellfish.
Food is the most common cause of severe allergy in young children, particularly cow's milk, soy, egg, peanuts, tree nuts 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.
One first has to be exposed to something to become allergic to it. It is currently believed that some infants may become sensitised after birth to small amounts of food passing intact through breast milk.
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 anaphylaxis. Skin or blood (RAST) allergy testing help 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.
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. These have no scientific basis, are unreliable and have no useful role in the assessment of allergy.
Most children allergic to cow's milk, soy, wheat and eggs 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.
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.
* When breastfeeding isn't possible, a suitable formula should be given up until 12 months to ensure adequate nutrition. Even in children with confirmed cow's milk and soy allergy, appropriate formulas are available on prescription from your doctor. This formula is usually based on cow's milk that has been processed to break down most of the proteins which cause symptoms in infants who are cow's milk allergic.
Since there is currently no way of "switching off" food allergies, the principles of managing food allergy are to:
Further information on food allergy and anaphylaxis is provided in accompanying articles in this series and on the ASCIA website www.allergy.org.au
References
Disclaimer
The content of this page has been reviewed by ASCIA members, represents the available published literature at the time of review and is not intended to replace professional medical advice. Any questions regarding a medical diagnosis or treatment should be directed to your medical practitioner.
For further information on allergies, asthma or immune diseases visit www.allergy.org.au - the website of ASCIA is the peak professional body of Clinical Allergists and Immunologists in Australia and New Zealand.