Updated 30 October 2017

What are the causes of asthma?

Just what causes asthma remains something of a mystery, but it's thought to be triggered by an allergy or when the lungs are irritated by something in the air.

Just what causes asthma remains something of a mystery, but it's thought to be triggered by an allergy or when the lungs are irritated by something in the air.

Asthma is regularly confused with other bronchial infections and doesn't always "present" in a straightforward way, making diagnosis difficult. But you're more likely to develop asthma if members of your family suffer from allergies, or have asthma themselves. This strongly indicates some underlying genetic/hereditary factors (such as proneness to allergies, certain immunological reactions etc.), as well as environmental factors/triggers.

It also appears to occur more regularly in people who are overweight.

The main factors involved in causing or aggravating asthma are:

1. Allergies
Asthma attacks are most commonly triggered by allergies to airborne particles or otherwise harmless stimuli like grass or tree pollens, dog and cat dander, cockroaches, dust mites, fungal spores and mildew. The house dust mite is the most common coastal and inland trigger factor amongst all races; even amongst indigenous populations where it was previously believed to be uncommon.

In some parts of the world grass, cockroaches and cat allergies have been identified as important triggers causing asthma. On rare occasions certain foods and additives may also trigger off asthma when taken by mouth.

An allergic reaction is implicated in about 90% of childhood asthma attacks and at least 50% of adult attacks.

This allergic reaction causes the lining of the airways (bronchi) in the lungs to become inflamed and swollen and the muscles of the walls of the airways go into spasm. As the airways narrow, it makes breathing difficult. The bronchial tubes then secrete mucus, which limits the airflow even further. Once you have a tendency to suffer from asthma, any of the triggers mentioned in this section, as well as cold air and stress, can trigger an attack.

2. Other co-existing conditions
A viral cold or flu can aggravate asthma symptoms temporarily. This effect may last for up to six weeks after the illness. In fact, most asthma attacks in both children and adults are caused by the common cold. The virus that causes a cold is usually the trigger factor. This fact has many implications. It means that people with asthma are sensitive to colds and must get good asthma therapy to prevent the cold-causing asthma attacks. This preventative approach is extremely important in asthma management and must be stressed.

Also remember that a cold is caused by a virus and that antibiotics won't work and shouldn't be used. You don’t need an antibiotic to treat a cold or an asthma attack.

Other conditions which may aggravate asthma include:

• Sinusitis: infection of the sinuses
• Nasal polyps: soft, round mucous-producing tissues that project into the nasal passages
• Gastroesophageal reflux disease (GORD): reflux (back flow) of stomach contents into the tube that leads from the throat to the stomach

3. Pollution
Once you have asthma, home and workplace chemicals, tobacco smoke, car exhaust fumes and certain chemical gases can aggravate an asthma attack. Children will even be affected by passively inhaling their parents’ cigarette smoke. Parents who smoke should be advised to stop smoking altogether. It is not enough for parents to avoid smoking in the presence of their child.

Chemicals and strong smells are transferred to children on the clothes of their parents and may trigger attacks. Smokers also have more germs carried in their throats which may affect their own children and trigger asthma attacks. Air pollutants from highly industrialised areas, changing eating habits to refined foods, and using anthracite and coal as fuel have been implicated in the increased prevalence of asthma.

4. Sport and exercise
Sport and exercise, particularly in cold weather, can set off an asthma attack. However, with the correct treatment asthma can be well controlled so that asthmatics need not avoid sport or exercise. In fact about 10% of Olympic athletes have asthma.

Exercise-induced asthma is no longer regarded as a condition separate from “normal” asthma, but rather one where “normal” underlying asthma is triggered by exercise. Exercise-induced asthma refers to the trigger, not a separate condition (e.g. pollen-induced asthma or workplace-induced asthma or smoke-induced asthma) and can be regarded as poorly controlled asthma.

5. Emotion
Emotion such as excitement, anger, fear or laughter can aggravate asthma. So-called "nerves" are not responsible for causing asthma.

6. Drugs/Medication
Certain commonly used medicines such as aspirin and other non-steroidal anti-inflammatory medication may trigger an asthma attack. Also be cautious when using "beta blocker" blood pressure tablets or eye-drops for glaucoma, as they may aggravate bronchoconstriction, and thus asthma, in adult life.

7. Occupational hazards
Asthma in adults can often be connected to the work they do and this is referred to as occupational asthma. Working with plastic resins, wood dust, grains, insecticides, and metals can make you susceptible to developing asthma later in life. But even cleaning products and work-related chemicals, including those used in photocopiers may make you vulnerable.

What you probably don't know is that new carpeting and furnishings often release formaldehyde, a common asthma trigger. If your office (or home) is being redecorated, increase ventilation to hasten formaldehyde dissipation. Adding potted plants to your workplace can also help clear pollutants.

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Asthma Expert

Professor Keertan Dheda has received of several prestigious awards including the 2014 Oppenheimer Award, and has published over 160 peer-reviewed papers and holds 3 patents related to new TB diagnostic or infection control technologies. He serves on the editorial board of the journals PLoS One, the International Journal of Tuberculosis and Lung Disease, American Journal of Respiratory and Critical Medicine, Lancet Respiratory Diseases and Nature Scientific Reports, amongst others.Read his full biography at the University of Cape Town Lung Institute

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