Asthma is a chronic lung condition that is characterized by difficulty in breathing. People with asthma have extra sensitive or hyper-responsive airways. During an asthma attack, the airways become irritated and react by narrowing and constructing, causing increased resistance to airflow, and obstructing the flow of the air passages to and from the lungs.

A few people seem to get asthma attacks only when they run or take other exercise.

In the past, doctors thought this was a different form of asthma. However, it is now known that it is very common for people with asthma to have asthma attacks during exercise.

This “exercise-induced asthma” is especially a problem for young people. In fact doctors used to puzzle over why children got exercise-induced asthma and why adults did not. Eventually research discovered the obvious reason : most adults do exercise as much as children.

Doctors now believe that people who get asthma attacks only when they exercise have asthma which is too mild to show up most of the time, needing the extra provocation from faster breathing to bring it out.

If the air you breathe during exercise is cold and dry, then the asthma will be worse. If it is warm and moist, the asthma will be less bad. This explains why swimming usually causes less asthma than outdoor running.

Increased breathing during exercise causes cooling and drying of the lining of the air passages and this is usually necessary for someone to get exercise-induced asthma. This explains why warm moist air protects against exercise-induced asthma. At this stage it is not understood why the drying and cooling of the airway linings causes the asthma episode.

Exercise is just one of many things which show that the air passages are being irritated or that you are an asthma sufferer.

This means things which are harmless to other people may trigger an attack of asthma.

To some extent people differ in which of these things cause the most asthma. Nevertheless, they all cause irritation or narrowing of the air passages in asthma sufferers.

So exercise is just one of many things which can provoke narrowing of the air passages in asthma. It is just one of many things which reveal the abnormal irritability or ‘twitchiness’ (called hyper-reactivity) of the airways which is an important feature of asthma.

Exercise-induced asthma can be useful for diagnosing asthma in a child. Exercising a child for about 6 minutes is a convenient and safe way of provoking a mild asthma attack, and this has led to many children getting early and appropriate advice and treatment.

Exercise-induced asthma has also been useful in asthma research. It can be used for testing the effectiveness of new medicines which may help treat asthma in the future. You will already have picked up some useful clues. Swimming rather than running, warmer and moister air, warm-up by short periods of exercise, and getting into training can all help.

Many cross-country skiers wear breathing masks which store some of the heat and moisture from the air they breathe out and return it to the air they breathe in. This is helpful in avoiding exercise-induced asthma.

In addition, taking control of your asthma, by using a ‘preventer’ treatment or by avoiding causes of asthma such as house dust mites and pets, can have a tremendously positive effect on exercise-induced asthma.

If you are a professional athlete, then you may be concerned about disqualification because you use drugs to control your asthma. The good news is that all the ordinary asthma medicines, used in the medically recommended way and dosage, are acceptable to sporting bodies provided you use them correctly for asthma. If you are in any doubt, then seek expert advice.

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