What causes asthma?

It is difficult to say for sure what causes asthma. What we do know is that:

you are more likely to develop asthma if you have a family history of asthma, eczema or allergies
it is likely that this family history combined with certain environmental factors influences whether or not someone develops asthma
many aspects of modern lifestyles – such as changes in housing and diet and a more hygienic environment – may have contributed to the rise in asthma over the last few decades
research has shown that smoking during pregnancy significantly increases the risk of a child developing asthma
children whose parents smoke are more likely to develop asthma
environmental pollution can make asthma symptoms worse and may play a part in causing some asthma
adult onset asthma may develop after a viral infection
irritants found in the workplace may lead to a person developing asthma (occupational asthma).

In this section