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What is asthma?

Over the last 20 years, the number of people with asthma in the Western world has doubled. About 5.4 million people in the UK have asthma. During an attack, the airways become inflamed, making them narrower. This causes wheezing, breathlessness and coughing. The triggers for an asthma attack vary, but may include allergy, cigarette smoke, infection and exercise.

An asthma inhaler.

What causes asthma?

If you suffer from asthma, you are also more likely to suffer from hayfever or eczema. Allergies can have many different causes, for example, pollen, house dust mites or animal fur. These triggers cause allergic reactions in some people but not others, partly because of differences in their genetic make-up. But the dramatic recent increase in people suffering from asthma means that genes are far from the whole story.

Asthma sufferers are often allergic to pollen.

How many genes have been associated with asthma?

Asthma tends to run in families. For most people, the risk of developing asthma is around 1 in 20, but if one of your parents has asthma, your risk rises to 1 in 4. Several genes are thought to be involved in asthma and other allergies. Some of them affect the immune system. There may be as many as 100 different genes involved. Research looks promising but it could be years before scientists know what they all are, and how they interact with other genetic and non-genetic factors.

Why the rise in asthma?

Since 1980 we have seen huge changes in diet, types of housing and heating, air pollution levels and medicines. Some scientists think that our use of antibiotics and antiseptics have produced an increasingly 'germ-free' environment. Fewer infections during childhood may mean our bodies are more likely to be oversensitive to harmless 'invaders', such as pollen. Researchers also think that childhood exposure to cigarette smoke may increase the risk of asthma. Whatever the environmental trigger, asthma may still only affect those who are already genetically susceptible.