The exact cause of asthma is unknown.
People with asthma have swollen (inflamed) and "sensitive" airways that become narrow and clogged with sticky mucus in response to certain triggers.
Genetics, pollution and modern hygiene standards have been suggested as causes, but there's not currently enough evidence to know if any of these do cause asthma.
Who's at risk?
A number of things can increase your chances of getting asthma. These include:
- having an allergy-related condition, such as eczema, a food allergy or hay fever – these are known as atopic conditions
- having a family history of asthma or atopic conditions
- having had bronchiolitis – a common childhood lung infection
- exposure to tobacco smoke as a child
- your mother smoking during pregnancy
- being born prematurely (before 37 weeks) or with a low birthweight
Some people may also be at risk of developing asthma through their job.
Asthma symptoms often occur in response to a trigger. Common triggers include:
- infections like colds and flu
- allergies – such as to pollen, dust mites, animal fur or feathers
- smoke, fumes and pollution
- medicines – particularly anti-inflammatory painkillers like ibuprofen and aspirin
- emotions, including stress, or laughter
- weather – such as sudden changes in temperature, cold air, wind, thunderstorms, heat and humidity
- mould or damp
Once you know your triggers, trying to avoid them may help control your asthma symptoms.
Asthma UK has more information on asthma triggers.
Page last reviewed: 19 February 2018
Next review due: 19 February 2021