The rise and rise of asthma
Key text
This topic is sponsored by Healthpact (now known as ACT Health Promotion Grants).
Australia has one of the highest rates of asthma in the world. It is a complex disease which is still not fully understood.
What is asthma?
Whenever we take a breath, we take air into our lungs through a complicated system of tubes, called airways. These airways empty the exhaust gases from our lungs and resupply them with oxygen-rich fresh air. Asthma is a condition where the airway walls become inflamed. The airways become narrower than usual and partially blocked, and may eventually become permanently damaged.
Asthma is a long-lasting problem – doctors call it a chronic disease. Sufferers can usually lead relatively normal lives (although they may be a bit breathless and have a frequent cough). Once someone has asthma, symptoms can be set off or made worse by triggers, leading to an asthma attack.
People suffering an attack will have some or all of these symptoms:
- difficulty breathing, or feeling out of breath for no reason;
- wheezing, especially when breathing out;
- tightness in the chest;
- coughing.
During an attack, the airways narrow because the muscles in their walls are squeezing them. This is called bronchoconstriction. In addition, more and thicker mucus is secreted into the airways, and their inner lining becomes inflamed and over-sensitive to any irritants. A severe asthma attack, if not treated in time, can prove fatal.
Causes of asthma
It is hard to know exactly what causes airway inflammation and asthma. Genetic factors play a part. Some people have an underlying predisposition. There is strong evidence that exposure to allergens in early life increases their risk of developing asthma. Asthma is also more likely to occur in someone with relatives who suffer from some form of allergy. Asthma can also be caused by exposure to some occupational sensitisers.
What triggers asthma symptoms?
Once the airways are inflamed, they become twitchy and oversensitive to different triggers, such as:
- allergens;
- polluted air, including cigarette smoke;
- infections of the airways (eg, colds);
- cold air;
- exercise;
- strong emotions.
But it is not always clear what triggers an asthma attack.
Types of asthma
Not all asthma is the same. There are two general types, sometimes called extrinsic (allergic) and intrinsic (non-allergic). About two-thirds of asthmatics suffer from allergic asthma and one-third suffer from non-allergic asthma.
Both types of asthma can be made worse by polluted air, even if it is not a trigger. This is especially true if the air contains sulfur dioxide, nitrogen oxides and ozone. These gases irritate the airways (as do many components in cigarette smoke), worsening an asthmatic’s condition.
Other factors also play a part in asthma. Some studies have suggested that the way we breathe and the depth of our breathing may affect the degree of tightness of the muscles that surround the airways.
Prevention and management
Unfortunately, there is as yet no real cure for asthma. The drugs used to treat it either prevent the occurrence of an attack, or relieve the symptoms of an attack (Box 1: Treatment options). When asthma is controlled by medication, exercise can be beneficial rather than acting as a trigger. Several top athletes are asthmatics.
Incidence in Australia
Asthma has been on the rise in Australia for many years; although the rise seems to have plateaued now. We have the dubious honour of being one of the world’s asthma hot spots. About 10 per cent of Australians have a problem with the disease, and about 20 per cent of children suffer from an asthma attack at some stage. Asthma ranks among the top ten reasons for visiting a doctor.
There are many theories about why the incidence of asthma is so high here. Ideas range from changes in asthma diagnosis (conditions that used to be classified as something else are now diagnosed as asthma) to the occurrence of house dust mites or large quantities of pollen.
Most Australian cities are situated in warm, humid areas – ideal conditions for house dust mites to thrive. The mites are so small that they are invisible to the unaided eye, but they breed in dust, carpets, mattresses and pillows. The mites are harmless, but when their droppings are inhaled they can trigger a reaction that makes some people sneeze and causes asthma in others.
But house dust mites are not the whole story. The rates of asthma around the world do not follow the known extent of dust mite infestations. Asthma rates are lower in less-developed countries and one authority suggests that the reduction in childhood respiratory diseases in our medically efficient world may cause the immune system in the lungs and airways to over-react when exposed to substances that it should tolerate. The 'hygiene hypothesis' suggests that our modern hygienic lifestyles may be contributing to an increased prevalence of asthma. Because children are being exposed to fewer infectious microorganisms, their immune system may develop differently, leading them to over-react to substances like pollen and dust mites.
Australian research into asthma
Throughout Australia, doctors and scientists are studying the causes and treatment of asthma (Box 2: Australian research).
Boxes
1. Treatment options
2. Australian research
Related Academy Material
Interviews with Australian Scientists
Professor Ann Woolcock (Medical science)
Page updated December 2011.