People with asthma have very sensitive airways that become inflamed and tighten when they breathe in anything that irritates them. This can cause chest tightness and wheezing and make it harder to breathe.

Most people with asthma who receive the right treatment – and take it correctly – can control their symptoms and lead normal lives.

What happens in asthma?

Your airways carry air in and out of your lungs. If you have asthma, they are very sensitive. Certain things trigger the muscles around your airways to tighten, making your airways narrower. The airway lining also becomes inflamed causing a build-up of sputum. This makes your airways even narrower. With narrow airways, it’s harder to get air in and out of your lungs.

normal airways diagram
airways with asthma diagram

Causes of asthma

We do not know what causes asthma, but we do know that many things can make it more likely that someone will get asthma.

Asthma often runs in families and people who have allergies – especially those under the age of 16 – are at a higher risk.

There are different types of asthma. Asthma associated with allergy usually starts in children. But some people develop asthma as adults and this is often not associated with allergic triggers.

Some people can develop asthma by repeatedly breathing in certain substances, especially while they’re at work, for example when they’re paint spraying, baking and welding.


What are the symptoms?

Symptoms of asthma include:

  • shortness of breath
  • wheezing – making a noise like a whistle when you breathe out
  • tightness in the chest
  • coughing

Sometimes the airways only narrow a little, resulting in mild symptoms. But some people’s airways can become so narrow that they can’t get enough oxygen into their lungs and their bloodstream. This is very dangerous and requires immediate medical attention.


What triggers symptoms?

Anything that irritates and inflames your airways can make your asthma worse. This could be an infection or something you breathe in. The air itself can make asthma worse, for example if you are breathing more quickly or if the air is cold or damp. Common situations – or triggers – are:

  • the common cold
  • allergies to things like pollen and animal fur
  • irritants, like tobacco smoke, spray cleaners and dust
  • heightened emotions
  • air pollution especially from traffic
  • Physical activity, particularly running in cold weather, can make asthma worse. This is sometimes called exercise-induced asthma. But don’t avoid exercise. Taking your reliever medication before exercise can often prevent symptoms.

How is asthma diagnosed?

Your health care professional makes a diagnosis of asthma based on your symptoms, family history of allergies and the results of breathing tests.

If you have asthma, your symptoms will tend to:

  • come and go over a period of time
  • be worse at night and in the early morning
  • be made worse when you come into contact with a trigger like smoke

Breathing tests help to confirm the diagnosis. People with asthma symptoms have narrowed airways so they breathe less air out. The amount of air you breathe out is measured by spirometry or by a peak flow meter, which you can use at home.