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What Causes Asthma?

Updated on February 25, 2012

There are numerous causes of asthma, some more important in one person than others. The first point to bear in mind is that asthma occurs in people predisposed to the condition, in other words, those with hyper-reactive airways. Bronchial hyper-reactivity may be inherited as it can be induced in symptom free relatives of asthmatic children and is much commoner in identical than non-identical twins. It is against this background of hyper-reactivity that the agents precipitating asthma act.


The commonest cause of an attack of asthma is a viral infection. Many parents will notice their child developing a cold, runny nose then start coughing. This may be followed by wheezing over the next day or two. Why such infections provoke asthma is uncertain, but it is thought that they stimulate the hyper-reactive airways to narrow. These infections are almost invariably due to viruses, which do not respond to antibiotics. So antibiotics are very rarely needed in the management of an acute episode of asthma. Viral infections are commonest in late autumn and winter, so childhood asthma is particularly common during these seasons.

Allergic factors

Asthma can be induced by agents to which the child is allergic. These are called allergens and include the following:


Pollens are carried in the wind and are inhaled. They may arise from trees, grasses or flowers and differ in various parts of the world. Pollens are only around at pollinating times which are usually only a month or so each year. They are obviously very difficult allergens to avoid.


Molds which are members of the fungus family, are widespread.

They are also carried around in the air. They are usually around in the warmer months, but can cause allergic symptoms indoors in the winter. High levels of molds occur in damp conditions such as rain and fog where they may be present in a damp room or in food storage areas, rubbish bins, wallpaper, upholstery etc.

House Dust

House dust is made up of lots of components: big particles and small particles. Anyone cleaning out a dusty room will cough and sneeze, but the asthmatic with his/her sensitive bronchi may well wheeze. House dust consists of pollens, hairs and skin scales from the family pet, fragments of clothing and upholstery, dead insects and bacteria, animal and plant fibers, food remnants etc.

Obviously it is not possible to protect oneself from all these normal things; however in practical terms, it is wise for the bedroom of an asthmatic child to be vacuumed and equipped with non-upholstered furniture, if that is possible. A foam mattress and pillow are preferable to avoid the dust in standard mattresses and pillows.

The main cause of house dust allergy is the house dust mite.

Mites live on human skin and are shed with the old skin scales onto the clothes or bedding. Mites flourish in damp, temperate places and are best kept under control by keeping the dust content of the home down and ensuring that it is as well heated and ventilated as possible.


The fur, or sometimes the skin, scales or saliva, of a pet dog or cat may also act as an allergen. Bird feathers and the fur of other animals may also have the same effect. Whilst the pet is around the symptoms will persist. If you are unsure if the pet is responsible for the problems, before giving him away, try asking someone to look after him for a month or so and see if the symptoms disappear.


Much has been said and written about food allergy not only in the context of asthma, but also in hay fever, feeding problems, hyperactivity and so on. Asthma is rarely caused by food allergies.

Food allergy when it occurs, is usually manifest by swollen lips and tongue, sometimes a rash and tummy pains and may be associated with coughing and wheezing. In other words, it is quite a dramatic event and usually the parents associate the symptoms with the food just taken by the child. If this does occur, that food should be avoided.

There are some preservatives in foods and soft drinks tartrazine sodium metabisulfite and monosodium glutamate which can cause problems. Sodium metabisulfite is used to preserve soft drinks and is broken down to the irritant gas, sulfur dioxide.

What usually happens is that with the first drink from the bottle or can, the child has a bout of coughing which may be associated with wheezing. This is a reflex response to the irritating sulfur dioxide. Children with these symptoms should avoid the offending soft drink. The effects of metabisulfite, MSG or tartrazine are not related to allergy, they are a direct effect of the chemical.

Environmental Factors

The environment that we live in, especially in cities, is polluted with fumes and other substances, all of which can probably precipitate an attack of asthma. Cigarette smoke can also do this either for the person smoking the cigarette or for those inhaling the 'second-hand' smoke. For children whose parents do not smoke, the incidence of asthma is 1.5 per cent, where one parent smokes it rises to 4.5 per cent and if both parents smoke, it rises to 8 per cent. Ideally parents of asthmatic children should not smoke.

Emotional Factors

This is a slightly confused area and folklore suggests that asthmatic children are 'nervous' children. This is untrue. However, it is accepted that emotional upsets, excitement or disappointment, can precipitate or aggravate an asthma attack. There is no particular personality type associated with asthma.


Very few medicines given m childhood provoke an attack of asthma. The main group of medicines that may do this are called beta blockers and are very rarely used in childhood. Aspirin may also induce asthma in aspirin sensitive patients and is best avoided.


Some children may develop an attack of asthma during or usually after moderate or strenuous exercise. For example, running about in the garden or playing an organized sport such as rugby. This is called 'exercise-induced' asthma. It is important that parents recognize this particular form of asthma in their child, if it occurs, as it can be almost totally prevented by appropriate medication, such as the use of a puffer, before exercise.

Changes in the Weather

Rapid climatic changes from hot to cold, or the other way around, can precipitate an attack of asthma. Some children are worse in damp weather, whilst others who are allergic to grasses are more likely to have attacks in the dry weather of the spring.

As can be seen there are many factors which precipitate asthma in a susceptible person. Some can be dealt with or avoided quite easily such as exercise, others like our environment are almost impossible to avoid.

Next: How is Asthma Diagnosed?


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