Allergic reactions occur when the body comes into contact with a harmless substance (an allergen) that it believes is invading it.  Allergens contain protein and can be dust, pollen, animal fur, grass, insects, milk, eggs and peanuts. Less common allergens are tree nuts, fruit and latex.  The immune system releases an antibody (IgE) to defend the body which in turn releases other chemicals that combine to cause symptoms of irritation and inflammation.

Blood, skin prick and patch tests are the common methods used to identify allergens.  The 'challenge test' is another method and is usually carried out in a hospital or specialist allergy unit.  Challenge tests involve introducing allergens to the lung (in the case of bronchial allergies such as asthma), nose or eye.  Food allergies can also be identified using a challenge test whereby the patient is given specific foods 'blind' to observe their effects.

From the results of your allergy intolerance tests, the specialist will be able to advise you on the cause and treatment of your allergy.  Treatment may be the removal of a specific allergen from your environment or the prescription of preventative or restrictive medication.

Allergy intolerance testing developed from research into hypersensitive reactions to environmental substances. In the early 20th century, Austrian paediatrician Clement von Pirquet noted that some of his patients who had a smallpox injection suffered severe reactions to a second injection. Von Pirquet, along with fellow paediatrician Bela Schick, later found that patients also suffered allergic reactions to innocuous substances like pollen, dust and certain foods.

Von Pirquet and Schick proposed that allergic reactions were caused by the immune system activating improperly and from then on all hypersensitive reactions were labelled 'allergies'. However, by 1963 a classification system for hypersensitivity was developed from the knowledge that hypersensitivity had more than one mechanism. 'Allergy' hypersensitivity was classified as 'type I hypersensitivity' and characterised by rapidly developing reactions.

One of the most important breakthroughs for allergy intolerance testing occurred in 1966 when Japanese scientist Kimishige Ishizaka discovered the antibody immunoglobulin E (IgE). IgE is the antibody that is released by the immune system when allergens are present. Currently one in four people in the UK are affected by allergies.

Allergy intolerance specialists employ different techniques. On finding an allergy specialist, ask about the methods they use, their expertise and some testimonials from previous clients.  Allergy intolerance testing employs four main methods:

1. 'Blood tests' involve taking a small amount of blood from a vein in the arm.  The blood taken is used to measure levels of immunoglobulin E antibodies in the system and results of the test can take between 7-14 days. 

2. The 'skin prick test' can detect over 350 allergens and involves a needle pricking the skin with a liquid containing the allergen specific to your allergic reaction.  A positive reaction will cause redness and itching with possible white swelling (known as a weal).  Results appear within 20 minutes and the test is usually the first test recommended for allergies.

3. A 'patch test' diagnoses delayed allergic reactions to the skin such as rashes or hives.  Various disc-shaped patches containing allergens are placed on the skin (usually on the back) and left for 48 hours.  The reactions are then observed to determine which allergen is the primary cause.  Patch tests are used to identify allergies to solvents, medications, dyes, cosmetics or preservatives.

4. 'Challenge tests' should only be carried out in specialist allergy units or hospitals as they involve introducing allergens to the lungs, eye, or nose and in the case of food intolerances, the stomach.  Check with your GP and local allergy specialist before undergoing this particular test.