What are asthma triggers?

An asthma trigger is anything that irritates your airways and makes your asthma symptoms worse. Asthma triggers can also cause asthma attacks. Cold weather or dust mites are examples of asthma triggers.

When you come into contact with an asthma trigger: 

• the muscles around your airways tighten    
• your airways become narrow and inflamed     
• you make sticky phlegm (mucus) that clogs your airways  
• you get asthma symptoms like coughing, breathlessness, a tight chest or wheezing  
• they may cause an asthma attack.

The main asthma triggers include:

• respiratory infections, such as colds, flu, respiratory syncytial virus (RSV), chest infections and COVID-19
• different types of weather, such as hot weather, cold weather and thunderstorms
• smoking and vaping
• hay fever and pollen
• different types of indoor air pollution and allergies, like damp and mould, dust mites and cleaning products
• outdoor air pollution
• exercise and physical activity
• pets
• strong emotions 
• stress
• food
• female hormones
• alcohol
• recreational drugs.    

You may have one trigger or lots of triggers. Everyone has different triggers, so what triggers your asthma symptoms might not affect someone else.

Some triggers are more common than others. For example, in a recent survey, 8 in 10 people with asthma told us that colds and flu triggered their asthma. Only 1 in 10 said they were triggered by food.

Some triggers affect you more at certain times of the year, such as pollen or colds and flu. Your surroundings can also affect your triggers. For example, if you live somewhere with mould or dust mites.

How you react to triggers might change over time too. If you’ve had uncontrolled asthma for a long time your airways can become more inflamed and more sensitive. This means you’re likely to react to asthma triggers more quickly and strongly.  

This is why you need to take steroid preventer medicine if you have asthma, to keep inflammation down in your airways.  Find out more about preventer inhalers. 

Knowing what your triggers can help you avoid them and lower your risk of symptoms.

Sometimes it’s obvious what your triggers are. For example, your symptoms may start quickly after you come into contact with an animal, or when you’re around cigarette smoke.  

But some triggers are not visible, for example pollen or indoor air pollution. Your asthma could be impacted by different triggers at the same time too. This can make it harder to know what’s causing your symptoms.

How do I work out my asthma triggers?

Keeping a diary of when you get asthma symptoms and what you were doing at the time might help you spot patterns and work out your triggers. If you use peak flow regularly, you could also use your peak flow scores to help you work out what’s triggering your asthma symptoms.  

If you’re finding it hard to work out your asthma triggers your GP or nurse can help. We know from calls to our helpline that sometimes it can be hard to contact your GP. We can help. We have advice to help you get a GP appointment.