What is an allergy?
An allergy is a sensitivity to a substance that does not usualy cause people any discomfort or harm. Hay fever, which is caused by a sensitivity to pollen, is a well known example. Asthma, eczema, rashes and a variety of other complaints can be caused partly or entirely by an allergy. In fact, allergies can affect almost any part of the body and be caused by a vast range of natural and artificial substances.
Allergies are a reaction to allergens, a name given to those substance such as pollen that spark off symptoms of an allergy in someone who is sensitive to it.
An allergy is everything from a runny nose, itchy eyes and palate to skin rash. It aggravates the sense of smell, sight, tastes and touch causing irritation, extreme disability and sometimes fatality. It occurs when the body's immune system overreacts to normally harmless substances.
Allergy is widespread and affects approximately one in four of the population in the UK at some time in their lives. Each year the numbers are increasing by 5% with as many as half of all sufferers being children.
Symptoms of an allergy tend to show up in/on the parts of the body that are exposed to the allergen. An airborne allergen like pollen, makes it severest impact in the eyes, nose and air passages.
There are three basic forms of allergic reaction affecting the skin. The most common especially among children is eczema. Dermatitis is a particular type of eczema affecting adults. This is caused by direct skin contact with certain allergens.
Eye and ear allergies
Allergic reactions can also affect the eyes. Theses generally show up as irritation and redness in the white of the eye. Severe swellings can occur but, but more often then not the symptoms are watering and soreness.
The ears are also often affected by allergens, when this happens the fluid will build up inside the ear and may temporarily affected your hearing.
Hay fever can affect the eyes and ears though the its principal target is the nose, which becomes stuffy, runny or sneezy.
Some people suffer from symptoms which are similar to those of hay fever, and will suffer with them all year round. They may have a stuffy, runny nose virtually all the time, although it will often be worse indoors, particularly at night and early morning. This condition is called Perennial rhinitis and can be the result of an to the common house dust mite.
Food allergies and food intolerance
These have a wide variety of symptoms. The most obvious symptoms of an acute food allergy are a stomach upset followed quickly by nausea, vomiting or diarrhoea. People who are acutely sensitive to a food may also get a swollen tongue and lips. Sometimes the suffer gets 2 kinds of symptoms; for instance a child who is allergic to cow's milk may get diarrhoea and a skin rash. Apart from skin rashes, which may appear hours or even days later after eating the food these symptoms become apparent almost imediatley after eating, usually within an hour. This makes it quite easy for the sufferer to identify the allergen.
Recurrent tummy pains and hyperactivity in children have been attributed to food 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.
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.
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.
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.
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.
If you have the acute kind of allergy that makes you sick whenever you eat say, strawberries or shellfish, you hardly need a doctor to diagnose your complaint. The cause and effect are obvious, and the simplest way to deal with the allergy is to avoid the allergen.
If your doctor carries out prick tests, he/she will be able to tell you which substance you should avoid. So if, for example you are allergfic to wool, then you should avoid contact with it.
Several kinds of drug are prescribed to deal with the symptoms of allergy.
Antihistamines combat the inflammatory effects of histamine when it is released. They come as tablets, liquid medicine, nose drops or eye drops, and there are injectable antihistamines which can be used to deal with serious attacks. Antihistamines are particularly useful for hay fever, urticaria and perennial rhinitis.
Another drug Disodium cromoglycate (bettter known as Intal), works by preventing the mast cells from exploding. This drug can be given in the form of an inhalant (for asthma), eye drops (for allergic symptoms in the eyes), tablets (for stomach allergies) or by a nose spray for hay fever or perennial rhinitis.
Corticosteriod drugs such as Cortisone, which are very powerful and anti-inflammotary, are some times prescribed for skin allergies or via an inhaler, to combat asthma.
Food allergies can sometimes be relieved by drugs, but some doctors prefer to recommend diets which ensure that you eliminate all the foods to which you have an allergic reaction. This can be quite difficult in the case of peanut allergy, which can be severe and most usually occurs in children. You should inform your childs school if your child has an allergy to nuts as peanut oil is a commonly used cooking ingredient in many foodstuff.
There is quite a lot you can do to help yourself or your child. Obviously if you sufer from a food or chemical allergy you should make every effort to avoid your allergens. (Reading the labels on food packets to see if the product contains the allergen you are alergic to).
Hay fever sufferers should be careful about going out in the open air during the pollen season, especially in mid-afternoon when the polen count is highest. Dark glasses can protect your eyes against pollen or spores.