Asthma basics

When a person with asthma comes into contact with something that irritates their airways (an asthma trigger), the muscles around the walls of the airways tighten so that the airways become narrower and the lining of the airways becomes inflamed and starts to swell. Sometimes, sticky mucus or phlegm builds up, which can further narrow the airways.

These reactions cause the airways to become narrower and irritated - making it difficult to breath and leading to symptoms of 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).

Symptoms of asthma