Food allergy, what is it, what triggers it and how it is diagnosed?

What is an allergy?

An allergy is the term which describes the body's reaction to a substance which is identified as harmful by the immune system. The immune system detects the substance which is known as an allergen and sets out to distinguish it from its own healthy cells, thereby causing an allergic reaction. When one has a food allergy, the immune system is identifying an item of food as an allergen. In order to defend itself from the invading substance, the allergen, it releases chemicals known as Histamines, resulting in the symptoms of an allergic reaction.

Generally an allergic reaction is unpleasant but not harmful. Rarely however, a severe reaction called an anaphylactic shock can occur, which can be fatal. The symptoms include dizziness, a rapid pulse, a rapid drop in blood pressure and swelling of the airways and throat, making it difficult to breathe. This can result in loss of consciousness if left untreated.

The symptoms.

The symptoms can appear from within minutes of eating the 'offending' substance to about an hour. The initial sensation might be itching or swelling in the mouth and throat and possibly difficulty swallowing and breathing. The symptoms might also include swelling, itching, rashes, nausea, vomiting, diarrhoea, abdominal pains, and sore, red and itchy eyes. On occasions, the symptoms might be confused with those of food intolerance.

Diagnosis of a food allergy is not always straightforward and it might take some time before your doctor succeeds in isolating the particular food that caused the reaction and confirm that you have an allergy. Often there are several conditions that might trigger the same reactions and your health care professional might ask some of the following questions in order to identify whether you are suffering from an allergy and if so, what it is that you ate that caused the reaction:

· How long after eating the suspected food did the symptoms appear?

· Was this the first time that you had suffered from such a reaction and, if not, is it associated with certain foods?

· If other people ate the food, did anybody else suffer from the symptoms? If the answer to this question is yes, then it probably is not an allergic reaction.

· How much did you eat prior to experiencing the symptoms? The severity of the allergic reaction can sometimes be associated with the amount of food eaten.

· How was the food cooked and stored.

If the doctor is unable to determine the diagnosis from the history of the reaction, he might ask the patient to keep a detailed record of all foods consumed over a period of time in order to associate the allergic reaction with the relevant food type.

The next step needed to identify what the patient is allergic to is the Elimination Diet. The patient is asked to withdraw the suspected food from his diet to see whether the symptoms disappear. He will then be asked to reintroduce it. If the symptoms return, a diagnosis can be made.

Another way of diagnosing a food allergy is the skin prick test. A tiny amount of the suspected food is placed on the skin of the forearm or back and the skin is then scratched with a needle and observed for swelling or redness, which would signify an allergic reaction to the substance. This test is not completely reliable though, as there can be a positive reaction to the test without having an allergic reaction when you eat the food. Where the patient suffers from dermatitis or eczema and it is not possible to carry out the skin prick test, a blood test might be carried out. The blood test, which is known as the Radioallergeosorbent test (RAST), measures levels of food specific antibodies in the blood. This test is also not completely reliable as often the body does produce antibodies, but they are not circulated in the blood.

So if the tests are completely unreliable, how can one know if he is allergic to a food? It would appear that ultimately it is up to the patient to try to keep a record of everything that they ate prior to getting the allergic reaction, thereby identifying what it is that they are allergic to.