Approximately 4 to 8% of children and 1 to 2% of adults have a true food allergy.

True food allergies are an unusual immunological response to the ingestion of the offending food. Virtually all known food allergens are proteins, and an individual must first be sensitised by exposure to the protein to develop antibodies, which then react to further exposures.

Food allergies need to be distinguished from food intolerances, which are generally caused by chemical agents, eg. sulphites, or certain genetic deficiencies, eg. lactose intolerance.

There are two stages in the development of an allergy, and the first is called sensitisation. This process happens when an allergen is encountered by the immune system and antibodies are made against it, despite it being harmless.

After sensitisation, the immune system retains a memory of the allergen and will recognise it if it meets it again. You do not always become sensitised the first time that your body meets a particular allergen – a substance may be tolerated for many years before an allergy develops.

Sensitisation can happen in utero and can also occur through breastfeeding

Once you have been sensitised, even a tiny quantity of that allergen can lead to an allergic reaction. If ingested, the allergen binds to the IgE present on the surface of the mast cells and basophils, and the toxic granules are released. If this reaction were the result of a parasitic infection, these chemicals would help to kill and digest the invading organisms.

If, however, the immune system is reacting against a harmless allergen such as peanut protein, these substances serve no useful purpose, but instead cause an increase in the blood supply to the tissues, leakage of fluid from the small blood vessels and local irritation.

The result is hotness, redness, itching and swelling in the affected area, and the production of excess watery secretions. In addition, the muscles of the airways in the lungs and the bowel may go into spasm, causing wheezing, shortness of breath, abdominal colic and diarrhoea. This process gives us the symptoms that we associate with allergy.

Allergy sensitivity is different for various individuals; different symptoms may be displayed after eating the same food product, and the symptoms exhibited can depend on the amount ingested. Some allergic consumers can tolerate certain amounts of the substance they are sensitive to, where as others may have a seemingly zero tolerance.

When a person has an allergic reaction, the symptoms can be displayed in a number of ways. One individual may exhibit several different symptoms, or just one. The symptoms will differ in severity for each individual, and for each individual, the symptoms may also depend on the various exposure circumstances eg. what was eaten, how much allergen was consumed, whether the individual has done exercise etc.

Symptoms can range from mild to severe, with most individuals suffering from just a few of the many possible symptoms. These can range from problems with:

• The respiratory tract -

rhinitis, asthma, throat swelling, (asthma is a rare response to food allergens)

• The gastrointestinal tract -

nausea, vomiting, diarrhoea, abdominal cramping, or

• The skin -

hives, itching, dermatitis, eczema

By far the most severe allergic reaction is analphylaxis, which can happen immediately that the food is eaten, or some time later. Individuals prone to analphylaxis need to carry a shot of adrenaline with them at all times in case they accidentally consume the product they are allergic to, and there is evidence to show that the severity of a reaction can be reduced and therefore the survival rate of analphylactics increased by treatment with adrenaline within the first few minutes of an anaphylactic reaction.

Anaphylaxis results in the dramatic lowering of blood pressure, swelling of the tongue, lips and throat which restricts breathing, a generalised shock reaction, and ultimately can result in death by multiple organ failure.

What are people most allergic to? There is a group known as the big 8 that cause about 90% of all allergic reactions, with hundreds of substances responsible for causing the other 10%. Basically if a food product contains protein, it has the capacity to cause an allergic reaction in a person who has become sensitised to that substance.

Living with an allergy, either yourself or someone in your family, requires great compromise to the quality of life. It takes longer to find products in the supermarket that are safe to eat because of the need to study food labels and scrutinise ingredient lists, and it costs more because generally cheaper products and house branded foods are labelled with may or does contain various allergens.

The only way to guarantee freedom from an allergic reaction is to avoid the offending foods all the time. This is where the food industry plays an absolutely critical role.