Information About Allergies

The most severe – though fortunately, quite rare – symptom caused by allergy is anaphylaxis. In this instance, the patient`s air passages swell and close and the blood pressure falls abruptly. This is an acute and life threatening condition, though it can be reversed very quickly by an injection of adrenalin.

Causes:-
The basic difference between people who suffer from allergies and those who do not is still not known. Allergies do tend to run in familiesn – and it is very common for people to develop hay fever, childhood eczema and asthma (a combined condition known as atopy). This may be due to an inherited characteristic in the cells which make up the immune system, which is the body`s defence system against desease.
Most allergies are are the result of an error in the imune system. The body`s defence forces react to the allergen as if it were a dangerous infected organism. White blood cells called lymphocytes are one of the most important elements of the immune system. Theses cells are constantly on the look-out for foreign substances such as bacteria, viruses and proteins which are different from the body`s own proteins and which may present a threat. When these white blood cells come across a potentially dangerous foreign protein they form a substance called an antibody, which combines with the foreign protein and neutralizes it.
By some highly complicated process, which is not yet understood by scientists, the immune system of a normal healthy person knows how to tell the difference between a dangerous foreign protein (like a virus) and a harmless one, such as food protein. But in an allergic person the imune system reacts to a harmless foreign protein as if it were a dangerous one, and starts forming an antibody. This antibody attaches itself to cells called mast cells. Mast cells contain a number of chemicals the most important of which is histamine.
When the body is exposed to the protein again, the antibody attached to the mast cells comines with the foreign proteins and tries to neutralise them. But in so doing, it upsets the structure of the mast cell, which falls apart and releases its load of histamine. The surge of histamine produces an effect very much like the inflammation which follows a wound; it makes tiny blood vessels dilate and they dilate their walls become leaky, so that fluid from the blood escapes into the surrounding tissues. The dialation of the tiny blood vessels causes redness and itching, and the escaping fluid makes the surrounding tissues swell. In hay fever the mocous glands in the nose and sinuses are also stimulated to produce fluid, which causes stuffiness and a runny nose.

Diagnosis
Skin prick test

In this test a small needle is used to gently prick the skin through a drop of fluid containing a known allergen. It is usually done on the forearm, although with young children it may be done on the back so they don’t have to see what is happening. The test is not painful and results are immediately available.

Blood test
In this test, a sample of your blood is taken and sent to a specialist laboratory for what is known as the RAST test (Radio AllergoSorbent Test) or CAP-RAST. This measures the amount of specific Immunoglobulin E antibodies (IgE) in your blood to various environmental and food allergens. House dust Mite IgE will be raised if you have an allergy to house dust mites and this is then graded 0 to 6 depending on the level of that IgE in the blood.

Patch test
This test is used to diagnose delayed allergic reactions such as Contact Dermatitis. It involves taping traces of various known contact allergens on the skin underneath special aluminium discs and keeping them there for 48 hours. It can test for allergy to Rubber, Nickel, Lanolin, dyes, cosmetics, solvents, preservatives, and medication. The test patches on the skin are then assessed for allergic eczematous changes by a dermatologist.

A specil diet called the elimination diet is sometimes used to identify which foods are the cause of a food allergy. At first a very plain diet is provided often consisting of little more than water and one vegetable such as potatoes and one meat such as lamb. All possible allergens are excluded.