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Causes and triggers of asthma

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 enough evidence to know if any of these do cause asthma.

Asthma symptoms can happen after exposure to a trigger. Sometimes your symptoms might start immediately. But sometimes they might not start until a few hours after exposure.

Keep a diary to keep track of your asthma symptoms and attacks. This can help you work out what triggers an attack.

When you know your triggers, avoiding them can help you control your symptoms. It can be hard to figure this out, but it will help you prevent asthma attacks.

Asthma triggers can include:

  • illnesses - viral and bacterial
  • lifestyle factors - food, cigarette smoke, stress
  • allergies - pets and animals, pollen, dust mites
  • environment - pollution, weather, indoor environment, damp and mould, the workplace

You can reduce your chance of having an asthma attack by using your preventer inhaler properly. You should bring your reliever inhaler with you in case you need it.

Non-urgent advice: Contact your GP if:

  • you are using your reliever inhaler more than 3 times a week


Viruses such as colds and flu can trigger asthma.

Cold and flu

Colds and flu can inflame your airways. This will cause them to make more mucus. This can cause an asthma attack or make it harder to breathe.

People with asthma are at greater risk from flu. You may not be able to avoid catching the common cold. But having the flu vaccine can help to prevent the virus from taking hold.

Everyone with asthma should have the annual flu vaccine and the pneumococcal vaccine.

Autumn is the best time to have vaccinations. You can get vaccinated at your GP or a local pharmacy.

A chest infection can make your asthma symptoms worse. Chest infections are more common in winter and often follow colds or flu.

Read more about chest infections


Your COVID-19 vaccine will help to prevent serious illness from COVID-19.

Asthma and COVID-19

Lifestyle factors

Lifestyle factors that can trigger asthma include smoking and eating certain foods.


Cigarette and second-hand smoke are often triggers for asthma attacks. 3 out 4 people with asthma will get wheezy in a smoky room.

If you smoke or are breathing in someone else’s smoke, you’ll have more symptoms and need more medicines to control your asthma.

Keep your home smoke free.

Stop smoking if you smoke. The HSE Quit Programme can help you stop smoking for good. Phone 1800 201 203 for help and support.


People with asthma do not usually have to follow any particular diet.

Some food additives and preservatives can trigger an asthma attack. This trigger is more common in children.

Food and drink and asthma - asthma.ie


Asthma can be triggered by stress. If you're going through a stressful period in your life, your asthma symptoms may get worse.

Stress and how it impacts you


Asthma can be triggered by allergies to dust mites, pets and animals or pollen.

Dust mites

If you're allergic to dust and dust mites, they might trigger your asthma. You might find that you have an asthma attack when you vacuum or sweep, or when you enter a dusty room.

Carpets and rugs can hold lots of dust. If possible, try to live somewhere with wooden floors.

Dusting with a damp cloth every week can help clear the dust in your home. You should wear a dust mask when you do this.

Wash your bed-clothes in a 60 degree Celsius wash every week. You can also cover your duvet, pillows and bed-clothes in allergy-proof covers.

Watch a video from Asthma Ireland about asthma triggers in the bedroom

Pets and animals

Being allergic to cats, dogs or other animals could be a trigger for your asthma. When your immune system reacts to the allergen, your asthma symptoms can be triggered.

You can become allergic to animals when you are older. The next time you spend some time away from your pet, see if your symptoms improve. That will show you if you're allergic to them. If you're allergic, you might need to rehome them.

Vacuum their hair and fur using a special vacuum cleaner designed for pet hair.


Up to 8 out of every 10 people who have asthma also have hay fever. If you have hay fever, pollen could be an asthma trigger for you.

Check the pollen forecast - met.ie

Use your preventer inhaler consistently and keep your reliever inhaler with you on these days.

Symptoms of hay fever are similar to colds. But colds usually go away after 1 to 2 weeks.

Hay fever is usually worse between late March and September, especially when it's warm, humid and windy. This is when the pollen count is at its highest.

You can treat your hay fever symptoms with antihistamines and nasal sprays containing corticosteroids. This is a type of anti-inflammatory medicine that will help reduce your symptoms.

If you start treatment quickly, you can manage your symptoms and reduce your risk of an asthma attack.


Environmental factors such as weather conditions or air pollution can also trigger asthma.

Changing weather

Due to changeable weather in Ireland, it can be hard to predict if the weather is going to trigger asthma symptoms for you. Keep your reliever inhaler with you, just in case.

Check the weather forecast on Met Éireann - met.ie

Hot weather

Keep your inhaler with you if hot weather can trigger your symptoms. Keep it in a cool-bag and out of sunlight. Air quality is usually better in the morning so try to get outside earlier in the day.

Cold weather

Cold air can shock your lungs and trigger an attack, especially if your asthma is not controlled. Wear a scarf around your nose and mouth to prevent this happening.


Thunderstorms can be a trigger for some people, due to the atmosphere before and during a thunderstorm. Stay indoors if possible when they're forecasted if they trigger your symptoms.

Work-related asthma

In some cases, there's a link between asthma and substances you may use at work. This is known as occupational asthma.

Some of the most common causes of occupational asthma include:

  • isocyanates - chemicals often found in spray paint
  • flour and grain dust
  • colophony - a substance often found in solder fumes
  • latex
  • animals
  • wood dust

People who may have a higher risk of being exposed to these substances include:

  • paint sprayers
  • bakers and pastry makers
  • nurses
  • chemical workers
  • animal handlers
  • timber workers
  • welders
  • food processing workers

Air pollution

Pollution can triggers asthma attacks.

Outdoor pollution can include car fumes, smog, ozone, and smoke. Check the air quality regularly and keep your inhalers with you on days when the air quality is not good.


We spend more time inside during the winter months. Keep rooms well aired to avoid your rooms becoming too warm. This should reduce asthma triggers such as dust and moulds.

Open fires and wood burning stoves can give off fumes that can trigger asthma symptoms. Use only the recommended fuel for your fire or stove. Keep your flues clear and chimneys swept to let the smoke escape properly.

Mould and damp

Mould and damp can be a trigger for your asthma. Moulds and fungi grow on walls and windows in damp houses.

To prevent mould and damp in your home:

  • use an extractor or open a window if you can when cooking or having a shower to prevent condensation
  • clean curtains thoroughly, especially bathroom curtains
  • dry washing outside, if you can
  • remove mould in bins by washing and disinfecting them

Page last reviewed: 9 December 2020
Next review due: 10 December 2023

This project has received funding from the Government of Ireland’s Sláintecare Integration Fund 2019 under Grant Agreement Number 9.