What is food allergy?
Food allergy refers specifically to adverse (untoward) reactions to a food in which the body’s immune (defence) system is directly involved. This is most usually the IgE antibody. For example, most people can drink a glass of milk or eat an egg without any problems. However, for a small number of people, their body’s immune system responds unfavourably to that food, and produces IgE antibodies against that food. Not all adverse reactions to food(s) involve the immune system. Non-immune (non-allergic) adverse reactions to food are termed food intolerance.
True food allergy always involves an immune mechanism (IgE or non IgE mediated) and should not be confused with the many causes of intolerances to food such as lactase deficiency, toxins contained in contaminated foods, food additives (e.g. tartrazine) and naturally occurring chemicals in food (e.g. tyramine in cheese).
The only reliable means of diagnosing food intolerance, and identifying the problem foods causing food intolerance, is by challenge testing.
How common is food allergy?
Food allergy affects about 5% of infants in the first year of life. In selected groups, such as children with eczema, the prevalence of food allergy may be as high as 20-30%. Food allergy is less common in adults (< 1% of the population).
What foods may cause an allergy?
Nearly any food can cause food allergy. Amongst the most common in children are cows’ milk, egg, peanut, fish, wheat and soya. The most common being peanut, egg and milk allergy.
What can of allergic reactions do we see?
Allergic reactions can be many types and happen at different times after eating the offending food. Some happen a few minutes up to an hour or two (early reactions). These early reactions often present as skin rashes or swelling of the face and/or other parts of the body, vomiting, a flare of eczema, a runny nose or asthma.
Other reactions can start many hours or even a day or two after eating the food (delayed reactions). These include pains in the stomach, vomiting, diarrhoea and eczema. In babies, food allergy can cause colic, but not all colicky babies have food allergy.
Rarely, a severe collapse that can threaten the life of a person (anaphylaxis) can be due to food allergy. It is therefore especially important that any severe reactions to a food be taken seriously.
Symptoms such as fatigue, hyperactivity and irritability have been implicated with food allergy, but this has not been substantiated.
How can food allergy be diagnosed?
A true allergic reaction will occur each time the problem food or foods are eaten. Thus, a careful description of what happens with different foods can be extremely helpful to the doctor to help him/her ascertain firstly that the patient really is food allergic and secondly, to identify what foods the patient is allergic to.
We do three types of tests to identify the food to which a patient may be allergic.
- Skin Prick Tests can be used to identify foods to which the patient is allergic. A nurse or doctor places a range of one up to several small drops of the suspected allergenic foods on the skin of the foreman, and a small prick is made through each drop of allergen into the skin. After 15 minutes the skin is observed for a wheal and flare reaction at each site on the skin. A red raised and itchy response indicates the food (s) to which the patient is allergic.
- Blood tests (“CAP-RAST”) can be used to identify a very wide range of potential allergenic foods. A small blood sample is taken by the nurse or doctor and sent to the laboratory for investigation.
- The Food Challenge Test is the most important test for the diagnosis of food allergy and identification of the problem food(s). This test must be performed only by specially trained staff.
How can food allergy be treated?
Avoidance of the offending food(s) is the best treatment. It is therefore particularly important to reliably identify the problem food(s). In infants and young children, it is advisable to eliminate as few foods as possible and for as short a period as possible. Avoidance-treatment must be under the guidance of a dietitian. Offending foods need not be eliminated for life. Cautious re-introduction of a “prohibited” food under the watchful eye of specially trained medical staff is usually attempted after 6 – 12 months. Medication is usually necessary if the allergic condition does not clear up even with avoidance of the allergenic food(s).
Will my child grow out of food allergy?
Most children grow out of their egg and milk allergy by 5 years of age. However, some very allergenic children will still have problems after this age, especially with fish and peanut, and sometimes with milk and other foods.