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.