Asthma Triggers: A Complete Guide to What Causes Asthma Attacks

Asthma Triggers: A Complete Guide to What Causes Asthma Attacks

The main asthma triggers in the UK (colds and flu, allergens, cold air, smoke and pollution, exercise, medicines and work), how they differ from causes, how to find yours, and how to cut your exposure.

Part of our asthma guide: symptoms, triggers and treatment.

Knowing your triggers helps you avoid attacks and need your reliever less. This guide covers the main types, how triggers differ from causes, and how to find and reduce yours. For seasonal triggers, see our guide to autumn asthma.

What Is an Asthma Trigger?

An asthma trigger is something that sets off symptoms, or an attack, in airways that are already sensitive. Triggers aren’t the same as the cause of asthma. Asthma itself is long-term inflammation that makes the airways overreact; triggers are the things that set off a flare-up on top of that.

This matters because a preventer (an inhaled steroid, on its own or in a combination inhaler) calms the underlying inflammation, so your airways react less to any trigger. Taking it every day is the most effective way to cope with triggers you can’t avoid. For more on what asthma is and why the airways become sensitive, see our asthma guide.

Allergens: Dust Mites, Pets, Pollen and Mould

House dust mites

Dust mites are tiny creatures that live in bedding, mattresses, carpets and soft furnishings. Their droppings are a strong allergen and a common trigger for allergic asthma, often all year round. Things that can help:

• wash bedding weekly at 60°C
• use allergen-proof covers on mattresses and pillows
• vacuum with a HEPA-filter vacuum cleaner and damp-dust surfaces
• keep bedrooms well aired and not too damp, as mites thrive in humid air
• choose hard floors rather than carpet in the bedroom if you can

Pets

Tiny flakes of skin, saliva and urine from animals are common triggers. Cat allergen is especially long-lasting: it can stay in a home for months after a cat has gone, and is carried on clothes into homes without pets. Dogs, horses, rabbits, guinea pigs and birds can also be triggers. Keeping animals out of your bedroom, washing your hands after contact, and regular cleaning help; an air purifier with a HEPA filter may help some people.

Pollen and mould

Tree pollen (spring), grass pollen (early summer) and weed pollen (summer into autumn) can all trigger allergic asthma. Pollen counts are highest on warm, dry, windy days. Mould spores, outdoors and in damp homes, peak in late summer and autumn. Thunderstorm asthma happens when storms break pollen grains into tiny particles that reach deep into the lungs; it can cause sudden, severe attacks, so keep your reliever with you on high-pollen stormy days.

Many people with asthma also have hay fever, and treating your hay fever can help your asthma control. See our guide to hay fever and asthma.

Colds and Flu: The Leading Trigger

Viral infections, such as colds, flu, RSV and COVID-19, are the most common trigger for asthma attacks in adults and children. They inflame the airways and can make them more sensitive for weeks after the infection itself has gone.

• have the flu vaccine each year if you’re offered it: it’s free on the NHS for many people with asthma, including those who need a steroid preventer
• have the COVID-19 and RSV vaccines if you’re eligible
• wash your hands often, and avoid close contact with people who have colds where you can
• when you’re ill, keep taking your preventer, watch your symptoms and peak flow, and follow your asthma action plan

Cold Air and Weather Changes

Cold, dry air takes heat and moisture from the airways, which can make them tighten. Stepping from a warm room into cold air is a common trigger, and so are sudden changes in temperature, humidity or storms. Wearing a scarf or snood over your nose and mouth warms the air you breathe. Keep your home warm, and keep your reliever with you in cold weather.

Air Pollution and Tobacco Smoke

Smoking, and breathing in other people’s smoke, both make asthma worse. Smoke irritates and inflames the airways and makes inhaled steroids work less well. If you smoke, stopping is one of the best things you can do for your asthma; your GP, pharmacy or local stop smoking service can help for free. Vaping can also irritate the airways.

Outdoor air pollution, such as nitrogen dioxide, ozone and fine particles (PM2.5), can also worsen symptoms. On high-pollution days, avoid busy roads, exercise away from traffic or indoors, and keep windows closed at peak times. You can check air quality on the UK Air Quality Index (DEFRA).

Exercise

Exercise can trigger symptoms, often peaking 5 to 10 minutes after you stop, because you breathe in lots of cold, dry air through your mouth. It’s worse in cold or dry weather. If your GP or asthma nurse has advised it, take 2 puffs of a blue reliever such as Ventolin Evohaler 10 to 15 minutes before exercise, or use your combination inhaler if you’re on AIR or MART. A warm-up helps too. With good daily control, most people with asthma can do any sport. See our guide to exercise-induced asthma.

Medicines That Can Trigger Asthma

• Anti-inflammatory painkillers (NSAIDs) such as ibuprofen, aspirin and naproxen can make asthma worse in some people. The NHS advises checking with a doctor or pharmacist before taking ibuprofen if you have asthma. Paracetamol is usually a suitable alternative.
• Beta-blockers, used for heart conditions and high blood pressure, and in some glaucoma eye drops, can narrow the airways. Make sure any prescriber knows you have asthma.
• ACE inhibitors, such as ramipril or lisinopril, can cause a persistent dry cough that may be mistaken for asthma. If you develop a cough after starting one, tell your GP.

Never stop a prescribed medicine without talking to your GP or pharmacist first.

Triggers at Work

Occupational asthma is asthma caused or made worse by something you breathe in at work. Common causes include:

• isocyanates (spray painting, foam and insulation)
• flour and grain dust (bakers, millers, farmers)
• latex (healthcare)
• animal proteins (laboratory and animal workers, vets, farmers)
• hairdressing chemicals such as persulphate bleaches
• wood dust (carpenters and joiners)
• solder fumes and some cleaning products

Suspect it if your symptoms are better on days off and holidays. Tell your GP your job; finding it early and reducing your exposure matters, because continued exposure can cause lasting damage. Your employer has a legal duty to control these risks; see the Health and Safety Executive guidance on occupational asthma.

Why Asthma Can Be Worse at Night

Many people notice their asthma more at night or early in the morning. Possible reasons include:

• Bedroom allergens: dust mites in mattresses, pillows and duvets, and pets that sleep on the bed
• Cooler air in the bedroom, or at night generally
• The body’s natural rhythm: the airways tend to be narrower in the early hours
• Acid reflux when lying down, which can irritate the airways
• A blocked nose from hay fever, leading to mouth breathing during sleep

Reducing bedroom allergens helps, but waking at night with asthma is a sign it isn’t controlled. UK guidance treats waking with asthma once a week or more as poorly controlled. Book a review with your GP or asthma nurse. See our asthma guide for the other signs.

How to Find Your Personal Triggers

• Keep a symptom diary for 2 to 4 weeks: symptoms, reliever use, peak flow and anything you were exposed to
• Check your peak flow to see whether readings dip after certain exposures
• Ask about allergy tests: skin prick or blood tests show whether you’re sensitive to dust mites, pets, pollen or mould
• Note work patterns: are you better away from work?
• Talk it through with your GP or asthma nurse at your yearly review, and add your triggers to your asthma action plan

Reducing Triggers at Home

• vacuum regularly with a HEPA-filter vacuum and damp-dust surfaces
• wash bedding weekly at 60°C and use allergen-proof covers
• deal with damp and mould, and air rooms well, especially bathrooms, kitchens and bedrooms
• avoid scented candles, air fresheners, incense and strongly scented cleaning sprays
• keep your home smoke-free
• keep windows closed on high-pollution or high-pollen days
• consider a HEPA air purifier in the bedroom if pets are a trigger

Avoiding triggers helps, but it doesn’t replace daily treatment. If you’re still getting symptoms more than twice a week, waking at night, or using your reliever often, book an asthma review. Our asthma inhalers guide explains the treatment options.

Safety, your GP and free NHS options

Ventolin and other asthma inhalers are prescription-only medicines in the UK. Before anything is supplied, a GPhC-registered pharmacist independent prescriber reviews your consultation, including the other medicines you take; some, such as beta-blockers, can make asthma worse.

• Relievers on their own: since 2024, UK guidance (NICE, BTS and SIGN) says no one with asthma should be treated with a reliever alone, and in April 2025 the MHRA told prescribers not to prescribe one without an inhaled steroid to people of any age with asthma. If you don’t use a preventer, we can supply a reliever once and will ask you to see your GP or asthma nurse.
• How many: up to 2 reliever inhalers per order. If you’ve needed 3 or more in the last 12 months, we’ll ask you to have an asthma review first; needing that many is linked to a higher risk of severe attacks.
• Read the leaflet in the pack, and ask a pharmacist or asthma nurse to check your technique.
• Report side effects to a pharmacist or doctor. You can also report them to the MHRA through the Yellow Card scheme.

We share your consultation with your GP because asthma needs ongoing care. Access Doctor is a private service, and there are free NHS options:

• Your GP practice: asthma reviews (at least once a year) and repeat prescriptions; many practices let you order repeats through the NHS App.
• Prescription charges: NHS prescriptions are free in Scotland, Wales and Northern Ireland. In England a charge applies unless you’re exempt, and a prepayment certificate can save money if you need several items.
• Urgent advice: NHS 111 (NHS 24 on 111 in Scotland), or 999 in an emergency.

For symptoms, triggers and how asthma is diagnosed, see our asthma guide.