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What Doctors Don't Tell You

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June 2020 (Vol. 5 Issue 4)

What triggers asthma?

About the author: 

What triggers asthma? image

Click here for your free Asthma Factsheet

Click here for your free Asthma Factsheet.

It can be difficult to identify exactly what triggers your asthma. Sometimes the link is obvious - for example, when your symptoms start within minutes of coming into contact with a cat or dog. But some people can have a delayed reaction to an asthma trigger, so some extra detective work may be needed.

Using a diary card to record your peak-flow readings and/or asthma symptoms will help you to identify your asthma triggers. Note the times when your symptoms are worse and anything that you might have come into contact with.

Avoiding the triggers

Once you have identified the things that bring on your asthma symptoms, you can take steps to avoid them. This can sometimes be tricky. It is likely that there will be many different things that trigger your asthma so you probably won't be able to avoid them all.

To get you started, here are the most common triggers and what you can do to avoid them.

Colds and viral infections

These are very common triggers of asthma attacks. They are also almost impossible to avoid. Using your inhaler regularly will reduce the risk of an asthma attack from colds or infections. A healthy diet with lots of fresh fruit and vegetables containing vitamin C will also help fight viruses. GPs recommend flu injections for those with severe asthma and for people over 60.

Housedust mites

These tiny insects (about 0.3-mm long) are transparent so you can only see them with a microscope. They live in the dust that builds up around the house, so you can find them in carpets, bedding, beds, soft furnishings and soft toys. Studies have shown that up to 85 per cent of people with allergic asthma are sensitive to housedust mite or, more specifically, their droppings.

Although you will not be able to remove all housedust mites from your home, there are a number of measures you can take to limit the effects of their droppings. Take the easier and inexpensive steps first to see if they improve your asthma. It is no use spending a lot of time, money and effort on dust control if you are not allergic to it.

Use barrier covers for your mattress, duvet and pillow, and wipe them with a damp cloth once a week. Make sure all the beds in the room are covered. Covers that completely enclose the mattress are better than ones only covering the top. Barrier covers need not be expensive, so shop around for ones that suit your budget.

Hot wash (at 60o C) sheets, duvet covers and pillowcases once a week. Keep soft toys to a minimum. Either hot wash them every one to two weeks, or put soft toys into a bag in the freezer for six hours. This kills the mites.

Vacuum all carpeted areas frequently. Use a vacuum cleaner that has good suction, and a filtered exhaust that doesn't scatter dust. Damp-dust all surfaces daily or use an attachment on your vacuum cleaner.

Use cotton or synthetic blankets instead of wool. They are easier to wash and are less likely to carry allergens. Although some people are allergic to feathers, there is no conclusive evidence to show that synthetic, so-called hypoallergenic pillows are any better. Whichever pillows you choose, use a barrier cover and wipe them over with a damp cloth once a week.

If these steps seem to work, you might also like to:

Choose short-pile synthetic carpet. It may be better than a pure wool carpet, although there is no conclusive proof for this. Replace carpets with lino, tiled or wood flooring. Plain, wooden bed frames are preferable to upholstered beds or headboards, which tend to collect dust.

Wash curtains every two to three months. Vertical blinds are often a better choice, but make sure you keep them free from dust.

Housedust mites love warm and humid environments, so you can reduce humidity levels in your home by keeping rooms well aired, using an extractor fan and/or opening windows during and after cooking, when you are doing the washing or using the bathroom.

Keeping the kitchen and bathroom doors closed to prevent damp spreading to other parts of the house also helps, as does removing damp and mould in the house quickly; avoid condensation by keeping the house well aired.

Cigarette smoke

Smoking is dangerous for everyone, but particularly for people with asthma. Inhaling cigarette smoke can irritate the lungs and bring on asthma symptoms. If you have asthma and smoke, you are increasing the risk of an asthma attack and may be permanently damaging your airways.

Passive smoking is particularly harmful to young children. If you are planning a baby, it is very important that neither parents smoke. Studies have shown that children of mothers who smoke are more likely to develop asthma. Other evidence suggests that, if a parent of an asthmatic child stops smoking, it can decrease the severity of the child's condition.

Inhaling other people's smoke is also hazardous for people with asthma.


Unfortunately, animals are a common trigger of asthma symptoms. The allergens are found in the pets' saliva and in very small flakes of skin (pet dander), fur and urine.

Studies have shown that using a vacuum cleaner with a filter can reduce levels of cat allergen in the air. However, these levels can increase by more than three times immediately after vacuuming. If cats trigger your asthma, it might be a good idea to persuade someone else to do the vacuuming, and stay out of the room until the allergens have settled.


Some people find that exercise triggers asthma symptoms. A study carried out by the Norwegian Institute of Public Health in Oslo suggests that baby swimming and infant respiratory health may be linked. The prevalence of recurrent respiratory tract infections was higher (12.3 per cent) among children who took part in baby swimming than among those who did not (7.5 per cent)-but perhaps more significantly, they were also the ones whose parents had a history of asthma, hayfever or eczema.

The main trigger for EIA appears to be cold, dry air. With aerobic exercise, there is suddenly a large increase in the volume of air that the body must moisten and warm.


Belgian research scientists have suggested that nitrogen trichloride, a powerful irritant and a byproduct of the chlorine used to disinfect swimming pools, could be linked to a growing incidence of childhood asthma.

The researchers measured levels of lung-specific proteins in the blood of primary school children who had swum regularly at indoor pools since their early childhood, and found a consistent and significant association between regular attendance at indoor swimming pools with lung-specific proteins (markers of lung permeability and epithelial damage).

The study calls for more epidemiological studies to be carried out "to verify if the increasing chlorinated pool attendance, especially by young children, could not be an important westernisation-associated factor in the rising incidence of childhood asthma and allergic diseases in industrialised countries", and suggests whether it wouldn't be better if we used non-chlorine-based disinfectants instead.


There are many different types of pollen grains (from grasses, trees and plants) that can trigger asthma symptoms in some people. Grass pollen is most likely to be a problem.

If grass pollen triggers your asthma it is important to review your treatment with your doctor or practice nurse before the hayfever season begins. On hot, dry days, avoid spending too much time outdoors. Avoid long grass, keep car windows closed, and look out for pollen forecasts on TV, in newspapers or on the Internet.

Poor air quality

Unfortunately, the air we breathe contains lots of different things that can make asthma symptoms worse. Air pollutants like cigarette smoke and car exhaust fumes release gases and particles into the atmosphere which can irritate your airways.

Ground-level ozone can be a problem for some people. Levels are likely to be higher on hot, summer days. If you think this might be a trigger for you, avoid exercising outdoors, especially in the afternoon.


Sudden changes in temperature, cold air, windy days and poor air quality on dry, still days can all affect your asthma. Take your usual dose of inhaler before going out on cold, dry days. Wear a scarf over your face if it's cold and windy. It will help warm up the air before you breathe it in. Try to avoid going out in the middle of the day on hot, smoggy days. Thunderstorms can also release large quantities of pollen into the air and trigger asthma attacks.


Moulds release tiny seeds called spores into the air. If you breathe these spores in, they can trigger asthma symptoms. Mould spores are found in any damp place-from piles of autumn leaves and woody areas to bathrooms, kitchens and even piles of damp clothes.


Perfumes are major asthma triggers. Watch out for hidden or unusual sources like furniture wax, plastic bin bags, inks, hair gel/spray, women's magazines and kitty litter.


Most people with asthma don't have to follow a special diet but, in some cases, certain foods can make symptoms worse. Dairy products (including cow's milk), eggs, shellfish, fish, yeast products and nuts are some of the offenders. Some people can have a severe, or anaphylactic, reaction to these foods.

Everyday medicines

Some medications can lead to asthma attacks. This occurs most often with medicines containing aspirin, non-steroidal anti-inflammatory tablets (NSAIDs, such as Nurofen) and beta-blockers used for heart disease.

UK researchers at the QueenElizabethHospital in Birmingham have recently suggested that taking large amounts of paracetamol regularly may deplete stores of glutathione, one of the major antioxidants present in the lung.


Another probable asthma trigger is vaccination. During a study of long-term breastfeeding, Dr Michel Odent and his London-based Primal Health Research Centre discovered, in a surprise finding, that children immunised against whooping cough were six times more likely to have asthma than those who hadn't been given the jab.


Besides iatrogenic causes, there is some evidence that emotional triggers play a role in asthma, particularly large airways obstruction. Perhaps the most telling evidence of the emotional cause of asthma is the number of trials which show that both treated and control groups get better, suggesting that mind-body treatments may be among the most effective.

Asthma and pregnancy

Generally speaking, a third of women with asthma report that their symptoms get worse during pregnancy, while a third says it stays the same and a third says it actually improves. One piece of good news is that asthma is least likely to cause a problem in the last few weeks of pregnancy, and very few mothers have symptoms during labour.

Feeling breathless as pregnancy proceeds is often a common experience, even for women who don't have asthma. Increasing weight, a growing baby in the abdomen, which prevents the lungs from expanding properly, a substantial increase in blood volume and a tendency to anaemia can all contribute to this.

Once you have made sure you are getting the best control for your asthma during pregnancy, what steps can you take to help ensure a healthy start for your baby? We know that asthma - like the related conditions eczema and hayfever - seems to be a condition that runs in the family.

There are steps you can take to reduce the chances of your baby developing asthma. Babies born to parents with allergic tendencies are at a higher risk of developing allergies if they are exposed to allergens in the first three to six months of their lives. This is one of the reasons why the Department of Health recommends that you do not give your baby foods containing eggs, nuts, cow's milk or wheat during the first six months.

And once your baby is born, you should try to breastfeed because vital nutrients are contained in breast milk, which helps to build up your child's immune system from a very early age.

Back to How You Beat Asthma

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