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Allergies - A Primer

What is an Allergy?

An Austrian doctor, Clemens von Pirquet, devised the word 'allergy' in 1905. He discovered that the body sometimes treats harmless substances in an unusual way. Normally our immune system ignores these harmless substances, but in allergic people it reacts to them by producing antibodies. Antibodies are proteins which act like soldiers - protecting the body from harmful invaders. However, antibodies which are produced in an allergic reaction cause distressing symptoms such as hay fever and harm the body rather than protect it.

Substances, such as pollen and dust mites, which may cause an allergic reaction are known as allergens. A substance that is an allergen for one person may not be for another - everyone reacts differently. But the likelihood of developing allergies is increased if other family members suffer from allergy or asthma

What happens when you have an allergic reaction?

When a person who is allergic to a particular allergen comes into contact with it, an allergic reaction occurs. This begins when the allergen (for example pollen) enters the body, triggering an antibody response (figures 1, 2, 3).
The antibodies attach themselves to special cells, called mast cells (figure 4). When the pollen comes into contact with the antibodies, the mast cells respond by releasing certain substances, one of which is called histamine (figure 5). When the release of histamine is due to an allergen, the resulting swelling and is extremely irritating and uncomfortable (figure 6). For instance, when you are allergic to cats and a cat scratches you, you get an immediate itchy swelling along the scratch line. This is caused by the release of histamine.

Examples of common allergens. The most common causes of allergic reactions are:

Similar reactions can occur to some chemicals and food additives.

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Date of Last Update: 07/27/12