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Asthma: causes and triggers


What are asthma triggers, and what are the causes?

We all know that all sorts of things seem to be able to bring on an asthma attack. Dogs and cats cause asthma attacks in some people. Tobacco smoke, cold air, exercise and even laughing can cause attacks too. On the other hand, people with asthma tell us that they are worse when they are anxious. Really bad attacks which force people to go into hospital often happen after a virus infection of your nose or chest. Some people get asthma if they take aspirin or other painkillers, and some get asthma from dusts or fumes at work.

In a way, these things are all causes of asthma.

Of course, other things help to decide whether you get asthma in the first place; not just one attack, but the disease as a whole. You can inherit the asthma tendency from your parents, although people with asthma should not worry about their future children on this score. Things to do with a 'Westernised' lifestyle in developed countries clearly have a lot to do with how many people have asthma in a country. Many people believe air pollution has something to do with it, though the evidence is very weak. Childhood infections and exposure to substances from bacteria in a dirty environment seem to protect against allergies, and this seems to be the main reason why richer populations have more allergic disease. So research may in future show us a way to get the benefits of infection without the harm and so reduce allergy.

So the causes of asthma are complicated. They include our genes, our exposure to things we become allergic to, and a general effect of our environment on the chance that these genes and things we become allergic to will cause trouble.

But in some ways it is not as complicated as it sounds.

Almost all asthma in young people is allergic asthma. This means that if you have asthma you probably have inherited genes which make it possible for you to get asthma, plus allergy-producing things in your environment, such as house dust mites, cats, or dogs. Both of these are causes, because if either of them were not present you would not have asthma.

But what about colds, exercise, laughter, or tobacco smoke, which can give you an attack of asthma even if everything in the last paragraph is true for you?

You can't cure your asthma by not taking exercise, or by not laughing. Quite simply, these are not causes of the fact that you have asthma, though they can be causes of the fact that you have an attack.

The words "trigger factors", or "triggers" of asthma should really be used for these things which can only cause an attack in someone who already has asthma.

But you hear these words used for the dog to which you may be allergic, or the cat, or the mould on the wallpaper which causes your asthma, and even about house dust mites. Instead of calling these things causes, which is what they are, people call them "triggers". That is a bit like calling the oncoming car the trigger of an accident. Demoting causes by calling them triggers makes people think they are not so important, and that maybe they should just keep taking the inhalers instead of making efforts to root out the cause of their asthma.

A cause is something without which an effect (such as asthma) will not happen. There may be more than one cause for an event. An extreme example is an election. Huge numbers of voters cause the result of the election: each vote was a cause.

We normally think of a trigger factor as something small, which causes something big to happen suddenly. A trigger is a type of cause. But the implication is that the important causes have to be there already if the trigger is to work, and that the trigger is not so important.

For example: if you don't have asthmatic lungs, or your asthma is really well controlled by treatment, a cold won't give you asthma symptoms. So in this sense, it is fair to call the cold a "trigger factor". Moreover, if you did not have colds, this would not stop you having asthma, so in that sense we can't call it a true cause of the disease.

But if you have asthma whenever you go near dogs, then dogs in the past have been the cause, and a dog now can cause an attack. In other words the dogs can be a cause of asthma and also a trigger of an attack. Concentrating only on the triggering of the attacks misses the really important point that contact with dogs was a cause of the asthma in the first place.

Confused? Here's another way to look at it:

A cause is something without which you would not be asthmatic.

A trigger is something which sets off an attack, but which does not make you asthmatic in the first place.

You will obviously want to avoid both causes and triggers, but the causes are more serious: without them the triggers do no harm. Causes include allergies to house dust mites, cats, dogs, and moulds.

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Housepainting can make asthma worse

We don't know of any research on this, but lots of patients tell us a consistent story. Glossy oil paints used for home decorating bring on asthma attacks in asthma sufferers. The good news is that emulsion paints don't seem to do this.

Polyurethane paints, usually recognisable because they come in two packs which need to be mixed together before use, cause occupational asthma in people who use them regularly. Probably they cause no great risk in people with asthma who use them infrequently. But it is surely a good idea to ventilate the area well when you are using any kind of housepaint.

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This page is maintained by Martin Stern
Created 1997. Last update: Oct 10 & 11, 2000 (substantial text edit, especially reference to infection and asthma prevalence).

Copyright © 1997, 2000 Asthma and Allergy Information and Research