What causes asthma?

It's difficult to say for sure what causes asthma.

What we do know is that you're more likely to develop asthma if you have a family history of asthma, eczema or allergies. It's 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 past few decades. Environmental pollution can make asthma symptoms worse and may play a part in causing some asthma

Research has shown that smoking during pregnancy significantly increases the risk of a child developing asthma. Similarly, children whose parents smoke are more likely to develop asthma.

Adult onset asthma may develop after a viral infection, and irritants found in the workplace may lead to a person developing asthma (known as occupational asthma).