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 birth weight

Some people may also be at risk of developing asthma through their job.

Asthma triggers

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
• exercise

Once you know your triggers, trying to avoid them may help control your asthma symptoms. Most children and adults with asthma have times when their breathing becomes more difficult. Some people with severe asthma may have breathing problems most of the time.

The most common symptoms of asthma are:

• wheezing (a whistling sound when breathing)
• breathlessness
• a tight chest – it may feel like a band is tightening around it
• coughing

Many things can cause these symptoms, but they're more likely to be asthma if they:

• happen often and keep coming back
• are worse at night and early in the morning
• seem to happen in response to an asthma trigger like exercise or an allergy (such as to pollen or animal fur)

See a GP if you think you or your child may have asthma, or you have asthma and are finding it hard to control.

Asthma attacks

Asthma can sometimes get worse for a short time – this is known as an asthma attack. It can happen suddenly, or gradually over a few days. Signs of a severe asthma attack include:

• wheezing, coughing and chest tightness becoming severe and constant
• being too breathless to eat, speak or sleep
• breathing faster
• a fast heartbeat
• drowsiness, confusion, exhaustion or dizziness
• blue lips or fingers
• fainting