Food allergy

• What is Food Allergy?
• Statistics
• Risk Factors
• Progression
• Symptoms
• Clinical Examination
• How is it Diagnosed
• Prognosis
• Treatment
• References

What is Food Allergy?

Food allergy refers to a specific allergic reaction, known as a type 1 hypersensitivity reaction, to a specific food (or foods), which is mediated by proteins known as IgE. Most food allergies in children are triggered by cows milk, egg, nut, sesame seed, soy, wheat and seafood proteins.
Food allergies can have effects at several different sites in the body, including the mouth, throat, lungs, skin and gastrointestinal tract. Often more than one site in the body is affected at the same time, and the reaction can be generalised, such as anaphylactic shock.

Statistics

The number of people with true food allergy is much less than often thought, with food allergy affecting 2-5% of children under 5 years and 1% of adults. Many children with food allergies tend to outgrow their allergies over time, however some allergies such as peanut allergy are usually present for life.

Risk Factors

People with atopic tendencies and other allergic diseases such as eczema, hayfever or asthma are more likely to develop food allergies, however food intolerances are not associated with allergic disease and the reasons why some people are more sensitive to natural chemicals found in some foods is unknown. Research is continuing to try to understand why some people develop food allergies while other people do not react to any foods. There are several theories currently being researched, but at this stage there are no general recommendations that can prevent the development of food allergy.
In children, cows milk, egg, peanut, soy, wheat and fish account for more than 85% of food allergens, while in adults, peanuts, tree nuts, fish and shellfish are responsible for most reactions.

Progression

Many children with food allergies to cows milk or egg outgrow their allergy by 5 years of age. Allergies to peanuts, tree nuts, fish and shellfish are more likely to be lifelong.

How is it Diagnosed

Investigations for food allergy are important, as it is often difficult to know which food is causing the reactions. Some of the reasons that the diagnosis of food allergy may be shown to be incorrect:

• Foods are rarely eaten on their own. For example, a cake may contain milk, eggs and peanuts, and investigations are required to determine which ingredient caused the reaction.
• Cooking food can change the protein structure of the food and make it more or less likely to cause a reaction (for example, pasteurised milk is less likely to cause a reaction than unheated milk, and roasted peanuts are more likely to cause a reaction than peanuts that are not roasted).

Some of the investigations that are available include skin-prick tests and radioallergosorbent testing (RAST), as well as oral food challenges. Skin prick tests and RAST can be useful to exclude food allergy, however, if they are positive it does not necessarily mean that a person will have an allergic reaction to that food if they eat it. See the section on skin-prick tests and RAST for more details.
Oral food challenges can be useful to confirm the diagnosis of food allergy, and they can also show the severity and type of reaction that occurs when the food is eaten. They can also be used to demonstrate that a person is no longer allergic to a particular food. The risks of oral food challenges includes severe reactions such as anaphylaxis, and it is important that these challenges are performed at a location where resuscitation facilities are available, which may mean at a hospital.

Prognosis

Food allergies are a common cause of anaphylaxis, which can be fatal. Anaphylaxis is more common with certain allergies, such as peanuts, tree nuts (such as almonds, hazelnuts, walnuts and pecans), fish and shellfish.
It is important that people with food allergies strictly avoid their allergens, know how to recognise symptoms of anaphylaxis, and ensure that friends and family are aware of their allergy. Most people recover completely after an anaphylactic reaction to foods and are able to live a full and complete life. However, it is important that strategies are put in place to avoid the foods that you are allergic to in order to prevent further episodes of anaphylaxis.

Treatment

The mainstay of treatment of food allergies is avoidance. This is especially important in food allergies where severe reactions occur such as anaphylaxis.
If a person with a food allergy is exposed to that food and has an allergic reaction, the best treatment is adrenaline, which is given as an injection such as EpiPen or EpiPen Junior. A written Anaphylaxis Action Plan should be provided by your doctor, which has step by step instructions for recognising a serious allergic reaction and how to treat it. The Australasian Society for Clinical Immunology and Allergy has an example of an Anaphylaxis Action Plan.

References

1. Björkstén B. Genetic and environmental risk factors for the development of food allergy. Curr Opin Allergy Clin Immunol. 2005;5(3):249-53. [Abstract]
2. Gold MS, Kemp AS. Atopic disease in childhood. Med J Aust. 2005;182(6):298-304. [Abstract | Full text]
3. Osborn DA, Sinn J. Formulas containing hydrolysed protein for prevention of allergy and food intolerance in infants. Cochrane Database Syst Rev. 2003;(4):CD003664. [Abstract | Full text]
4. Osborn DA, Sinn J. Soy formula for prevention of allergy and food intolerance in infants. Cochrane Database Syst Rev. 2004;(3):CD003741. [Abstract | Full text]
5. Roberts S. Challenging times for food allergy tests. Arch Dis Child. 2005;90(6):564-6. [Abstract | Full text]
6. Sampson HA. Food Allergy. J Allergy Clin Immunol. 2003;111(2 Suppl):S540-7. [Abstract]
7. Sampson HA. Food anaphylaxis. Br Med Bull. 2000;56(4):925-35. [Abstract | Full text]
8. Swain A, Soutter V, Loblay R. Friendly Food. Sydney, NSW: Murdoch Books; 2002. [Book]
9. Warrell DA, Cox TM, Firth JD, Benz EJ Jr. Oxford Textbook of Medicine (4th edition). Oxford: Oxford University Press; 2003. [Book]