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Hay fever, asthma and eczema are more common than ever before. Such allergies can cause real discomfort and inconvenience. However, the latest research is uncovering new treatments - and possible cures.

An allergy is a sensitivity to a substance which does not normally cause discomfort or harm. Allergies can affect almost any part of the body and are caused by a vast range of natural and artificial substances.

Substances that trigger the symptoms of an allergy are known as allergens. These can include foods, pollen, spores, insect bites, animal fluff, certain chemicals, drugs and house dust mites. Some people are even 'allergic' to heat or cold.

In many cases, it's possible to identify allergens which trigger the condition - either in food or in substances which come into contact with the skin - but sometimes they are difficult or impossible to detect. It's still not known exactly why some of us are prone to allergies.

They do tend to run in families, and a genetic background boosts your risk fourfold. This link may be due to inherited 'pro-allergy' genes, but environmental influences are important, too.

Allergies develop when the immune system, which defends our bodies against disease, overreacts to a normally harmless substance.

White blood cells (lymphocytes) produced by our immune system are constantly on the look-out for foreign substances such as viruses, bacteria and foreign proteins.

The immune system of a healthy person recognizes the difference between a foreign protein like a virus and a harmless one, such as a food protein.

In people prone to allergies, for reasons not fully understood, the immune system reacts to harmless proteins as if they were dangerous. The white blood cells change into plasma cells, which create antibodies when an allergen is present. The antibodies are thought to attach themselves to special cells called mast cells, which contain a number of chemicals including histamine.

The next time the body encounters those proteins, the antibodies combine with the foreign proteins and tries to neutralize them. This triggers the break-up of the mast cells, which fall apart and release the chemicals into the bloodstream.

These chemicals are responsible for a whole range of allergic reactions, such as redness, itching, and swelling of nasal passages, as well as the stuffy nose of hay fever and the itchy weals of urticaria. Other common allergic reactions include narrowing of the muscles in the airways, evident in asthma, and the production of excess nasal fluid seen in hay fever.

Allergic symptoms tend to show up in the parts of the body which are exposed to the allergen. An airborne allergen, like pollen, affects the eyes, nose and air passages; food allergies reveal themselves through swollen lips, diarrhoea or stomach upsets, while allergies to metal and rubber will usually result in skin rashes.

However, if an allergen gets into the bloodstream, it can cause reactions almost anywhere in the body. This is particularly true of food allergens, which are absorbed into the bloodstream through the digestive system.

Eczema, the most common form of skin allergy, appears as a rash or area of scaly skin that is found mostly on the hands, face, neck and in the creases of the forearms and behind the knees. The inherited type, atopic eczema, is especially common in babies and children.

Contact eczema, or dermatitis, which often affects adults, is caused by direct skin contact with certain allergens. It often affects the hands and can be caused by soaps, detergents, washing powders, glues or other substances or chemicals encountered at work.

Some people are allergic to nickel, found in costume jewellery and fastenings on bras or jeans. A red blistery rash develops where the nickel is in contact with the skin.

Urticaria is often called nettle-rash because the red itchy weals resemble nettle stings. The rash usually appears suddenly, and may affect just a small area. However, in severe cases it can cover the whole body. Foods, drugs, perfumes and even exposure to heat and cold can all be to blame.

The main target of hay fever, or seasonal rhinitis, is the nose, but it can also affect the eyes and ears. Unlike a common cold, which usually lasts for only a few days up to a week, hay fever lasts for as long as you are exposed to the pollen to which you are allergic.

Some people suffer symptoms similar to hay fever all year round. They have a stuffy, runny nose virtually all the time, which is often worse when indoors, particularly at night and in the early morning. This condition, called perennial rhinitis, is often the result of an allergy to the house dust mite.

The most obvious symptoms of an acute food allergy are digestive disturbances like nausea, diarrhoea, or vomiting, but there may be other symptoms such as skin rashes, or a swollen tongue or lips.

These symptoms - usually with the exception of skin rashes - come on almost immediately after eating the allergen, which makes it quite easy to identify the culprit.

Evidence shows that conditions such as irritable bowel syndrome, colic in babies and asthma attacks can all be food-related.

More controversial is the idea that food allergies lie behind a much wider range of conditions, both physical and emotional. These include depression and anxiety, migraine, headaches, schizophrenia and hyperactivity in children.

If you suspect you have an allergy, see your doctor. If necessary, he can refer you to a special allergy clinic. You may be asked to keep a diary, detailing your symptoms and any allergens you've been exposed to over a period of months.

You may be given a skin prick test. This can involve dropping a watery solution containing a small amount of a particular allergen onto your forearm, and pricking the skin so that some of the allergen enters your system. If you are allergic to that substance, a round, red weal appears within about 15 minutes.

Nasal allergies are sometimes diagnosed using a 'challenge' test. Allergens are sprayed into your nose, inhaled and then exhaled to determine if a reaction occurs.

A patch test may help show up skin allergies. Special patches are impregnated with various allergens and then applied to your skin, usually on your back. The patches are left on for at least a couple of days before a reaction appears. Blood tests, which involve measuring the amount of allergy antibody in the blood, may also be carried out.

A special elimination diet, which involves first cutting out and then reintroducing suspect foods to see if they cause a reaction, may be used both to identify the cause of a food allergy and to treat it.

Antihistamines - which block the activity of histamine - are useful for relieving the symptoms of allergies such as hay fever, urticaria, and perennial rhinitis.

Drugs like sodium cromoglycate work by preventing mast cells from exploding. They can be used for asthma and other nasal allergies and, in some cases, for food allergies. Other drugs include corticosteroids, which mimic the action of anti-inflammatory hormones.

Desensitization involves injecting small quantities of an allergen over a period of time to build up immunity. Though not often carried out by the doctor, this may be tried if drug treatment is ineffective.


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