Allergy occurs when a person's immune system reacts to substances in the environment that are harmless for most people. These substances are known as allergens and are found in dust mites, pets, pollen, insects, ticks, moulds, foods and some medicines.

Atopy is the genetic/inherited tendency to develop allergic diseases. People with atopy are said to be atopic.

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When atopic people are exposed to allergens they can develop an immune reaction that leads to allergic inflammation (redness and swelling).

This can then cause symptoms:

•           nose and/or eyes - hay fever (allergic rhinitis/conjunctivitis)

•           skin - eczema, hives (urticaria)

•           lungs - asthma

A substance that is an allergen for one person may not be for another - everyone reacts differently. The likelihood (or risk) of developing allergies is increased if other family members suffer from allergy or asthma.

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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. The antibodies attach themselves to special cells, called mast cells. When the pollen comes into contact with the antibodies, the mast cells respond by releasing certain substances, one of which is called histamine. When the release of histamine is due to an allergen, the resulting swelling and inflammation is extremely irritating and uncomfortable.

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The most common causes of allergic reactions in Australia are:

•           dust mites

•           pollen (grass, weed or tree)

•           foods such as peanuts, cow's milk, soy, seafood and eggs

•           cats and other furry or hairy animals such as dogs, horses, rabbits and guinea pigs

•           insect stings and tick bites

•           moulds

•           medicines

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Similar reactions can occur to some chemicals and food additives, however if they do not involve the immune system, they are known as "adverse reactions" rather than "allergy".

 

Which areas of the body may be affected?

Depending on the allergen and where it enters your body, you may experience different symptoms. For example, pollen, when breathed in through the nose, usually causes symptoms in the nose, eyes, sinuses and throat (allergic rhinitis). Allergy to foods usually causes stomach or bowel problems, and may cause hives (urticaria).  Allergic reactions can also involve several parts of the body at the same time.