When immune systems go wrong

ALLERGIES are caused by the human immune system making a mistake.

A properly functioning immune system is supposed to identify and destroy many invading viruses and can destroy cells that become cancerous.

But a hypersensitive system misidentifies otherwise innocuous substances, such as chemicals contained in certain foods, as harmful and then attacks the substance with a ferocity far greater than required.

The problems this can cause may be mildly inconvenient and uncomfortable, such as mucus build-up or sneezing.

In more serious cases it can lead to the total failure of the organism the immune system is supposed to be protecting.

An example of this would be extreme reactions to peanuts, which can kill either by laryngospasm (instantaneous swelling and closing of the vocal cords) or by anaphylactic shock, which can take place over a period of hours after exposure and can lead to a fatal drop in blood pressure.

Supermarkets and food producers have come under increasing pressure, and in some countries are legally obliged, to clearly identify any foods which may contain items that could trigger common allergies.

Nuts and nut oil are increasingly being used in cooking and can often be a hidden ingredient in dishes such as lasagne, salads and desserts.