An asthma ‘trigger’ is anything that brings on or aggravates asthma symptoms.
Common asthma triggers can be divided into roughly 2 groups:
- substances called allergens that set off an allergic reaction in the body and aggravate asthma symptoms; and
- other substances and circumstances that aggravate asthma without involving an allergic reaction.
Knowing what your asthma triggers are, and then avoiding them (if possible), are important for achieving good asthma control.
House dust mites
These are tiny creatures related to ticks and spiders that live by the tens of thousands in the dust of our homes, especially if the air is warm and humid. Inhaling dust mite droppings can trigger asthma symptoms.
Pollen (usually from grasses, trees or weeds)
As well as causing hay fever in people with a pollen allergy, pollen can also trigger asthma symptoms in susceptible people.
In Australia, pollen levels in the air are at their highest in spring and early summer, although grass pollens can cause a problem all year round for people living in the warmer northern regions of the country.
Many of the pollens that trigger asthma are from introduced plant species such as Ryegrass, Paterson’s curse and Pellitory weed (‘asthma weed’), and street trees such as oaks, elms and birch.
Some people are affected by a phenomenon called ‘thunderstorm asthma’ — asthma that is triggered by the combined effects of weather conditions, pollens and other airborne allergens.
Thunderstorm asthma is thought to be caused by several mechanisms:
- the high humidity before a thunderstorm, which can cause pollen grains to break apart and release tiny starch granules that can be breathed into the lungs more easily than larger, intact pollen grains;
- the increased concentration of airborne asthma triggers during thunderstorms; and
- changes in temperature and humidity.
Animal dander (skin scales or flakes from the hair or feathers of animals)
For some people with asthma, touching and stroking an animal, or just being in the same room as a pet or where that pet has been, can trigger a reaction.
This is because of an allergy to the animal’s dander (skin scales or flakes from the fur or feathers of animals), or even their saliva or urine. In homes with pets, dander makes up a large component of household dust and it can float in the air and settle on surfaces around the home, so you may not even need to have contact with the pet itself to trigger a reaction.
Some people with asthma may also find they are allergic to other animals with which they come into contact, such as horses, rabbits, guinea pigs, and birds, even though these are kept outside.
The most effective way of treating pet allergy is to remove pets from the home. However, before you make any decision about the future of the family pet, see your doctor if you suspect that you, or a member of your family, might be allergic to your pet.
Your doctor can organise special skin or blood tests to diagnose allergies to animals, if necessary. Skin prick tests are convenient and simple to do. A drop of an extract of the substance thought to be causing the allergy (allergen) is put on the skin and a needle is then pricked through the drop of allergen into the skin. The size of the inflamed area of the skin — called a wheal and flare reaction — indicates the strength of the allergic reaction.
Even if you decide to remove pets from your home, it can be some time before a change in the allergy is obvious. It’s estimated that the presence of pet allergen can persist for 3 to 6 months, or in some cases years, after a cat is removed from a house.
Other changes that you can make to try to lessen the effects of pet allergy on your asthma include the following.
- Wash your hands after contact with pets, and don’t touch your face before washing your hands.
- Keep your pet outdoors if possible.
- If your pet lives indoors, restrict them to as few rooms as possible.
- Keep pets off chairs, couches and other soft furnishings.
- Keep pets out of your bedroom.
- Frequently vacuum with a vacuum cleaner that has a good filter system — such as a HEPA (high efficiency particulate air) filter.
- Clean hard floors with a damp cloth or steam mop.
- Change and wash clothing often if you cannot avoid being near animals, as pet allergen can be carried on clothing. Clothes should be washed in water hotter than 55 degrees Celsius.
- Pets should be washed and groomed as often as the vet recommends.
Moulds or fungi
Alternaria is an outdoor fungus that is found on plants. It is known to trigger asthma in drier inland areas of Australia, especially in agricultural regions when crops are harvested. Cladosporium is a plant mould that can also trigger asthma, but is more common in cooler areas of southern Australia and can be a problem when grass is mown.
Moulds that grow indoors — for example, on damp walls, especially in corners — can also trigger asthma.
This allergen, which is found in cockroach droppings, can build up in the dust of houses that have cockroaches present, and can trigger asthma symptoms.
Some adults can develop an allergy to substances that are present in the air at their workplace and can trigger asthma symptoms, for example, flour, latex and wood dusts.
Some other workplace asthma triggers, such as isocyanates, which are used in the manufacture of pesticides, polyurethane foam, plastics, paints and varnishes, may trigger asthma symptoms either via an allergy or because they irritate the airways directly.
Viral infection of the upper airways (such as colds and flu) is a common trigger of asthma, especially in children.
People with asthma and allergies are at higher risk of asthma flare-ups from colds and flu than those without allergies.
Asthma can be triggered by certain medicines such as:
- non-steroidal anti-inflammatory drugs (NSAIDs);
- heart and blood pressure medicines called beta blockers;
- certain eye drops; and
- complementary medicines, including Echinacea and bee products (including royal jelly, pollen and propolis).
Air pollution and other inhaled irritants
Airborne pollutants (including course and fine particulate matter, ozone and carbon monoxide) can trigger asthma symptoms. Exhaust fumes, in particular from diesel engines, are thought to contain particles that stick to common airborne allergens, for example broken-up pollen grains, and make them easily breathed into the lungs, where they can trigger asthma symptoms.
Other inhaled irritants that can trigger asthma symptoms include:
- bushfire smoke;
- smoke from indoor wood fires;
- cigarette smoke;
- fuel combustion heaters that emit nitrogen dioxide, such as unflued gas heaters;
- some perfumes;
- incense; and
- the fumes from paints and cleaning fluids.
Exercise is a very common asthma trigger and may be the only trigger in some people with asthma. It is thought that breathing in cold, dry air while needing to breathe hard, as occurs with vigorous exercise, are the key elements of this trigger. That being said, exercise and being active is important for general health, and people with well controlled asthma should be able to participate in most forms of exercise without restrictions.
Strong emotions such as stress, anxiety, and hearty laughing or crying can trigger asthma symptoms in some people.
A small amount of stomach acid refluxing or regurgitating into the lower oesophagus, as occurs in heartburn, is a potential asthma trigger.
Cold air and ambient temperature changes
Breathing in cold, dry air can trigger asthma symptoms, for example, outside air on a cold day or cold night-time air in your bedroom.
Foods are rarely a trigger for asthma, however some food additives can trigger asthma. These include sulphur dioxide and sulphites (food additive numbers 221 to 228) — found in sausages, dried apricots, wine and many ‘fast foods’. Sulphur dioxide (additive number 220) is the one thought most likely to trigger asthma symptoms.
Tartrazine (a food dye, additive number 102) is another possible trigger of asthma, although research has not shown a firm link between tartrazine and asthma symptoms.
Glutamates are found in many foods naturally or are added as flavour enhancers (food additive numbers 620 to 625). One of these additives, monosodium glutamate (MSG; additive number 621), has been studied a great deal; however, research has not clearly shown that MSG can provoke asthma symptoms.
There is not enough evidence to suggest that people with asthma should routinely avoid food additives without having first been referred by their doctor to an allergy specialist.
Some women find that their asthma symptoms worsen in the pre-menstrual phase of their menstrual cycle. Pregnancy also causes a worsening of asthma control in about a third of women with asthma.