Asthma

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What is Asthma?

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Contact Andrew Walbank.

Asthma is a disease of the lungs. People with asthma experience episodes of asthma, or asthma attacks. This occurs when there is a narrowing and inflammation of the airways, which makes it harder to breathe.

The lungs provide an interface between the air that we breathe in and the bloodstream. When a person breathes, air is drawn in through the nose and mouth and down through the trachea. The trachea divides into two bronchi, a right main bronchus and left main bronchus, to supply each lung.

The bronchi divide into smaller bronchi, and then into bronchioles which ultimately terminate in the alveoli - the folded membranes where gas exchange takes place. The bronchi and bronchioles have a muscular layer in the wall which allows them to contract. In an acute asthma attack, this muscular layer contracts and leads to narrowing of the airways.

Inflammation may still be present between asthma attacks. This makes the airways sensitive and more likely to react to asthma triggers and cause an acute asthma attack.

Click here to learn more about the respiratory system.

Asthma is sometimes divided into four main groups as follows:

Atopic asthma: This is the most common and classic type of asthma. Patients normally have relatives who have atopic asthma, and themselves experience other allergic diseases (e.g. food allergy, eczema, hayfever). House dust mites (HDM), pollen and animal fur are common triggers.
Non-atopic asthma: This type is triggered by respiratory infections in patients without a family history or other allergic traits.
Drug-induced asthma: Aspirin medication can sometimes induce asthma attacks and urticaria in susceptible individuals.
Occupational asthma: This form of asthma is induced by small quantities of chemicals and fumes, usually following repeated exposure.

Who gets Asthma?

Asthma is a common disease affecting more than 2.2 million Australians. Approximately 1 in every 6 children, 1 in 7 adolescents and 1 in 9 adults in Australia currently have asthma. These rates are considered high compared to the rest of the world. The worldwide number of people with asthma is increasing, especially in developed countries such as Australia.

Asthma is less common in some countries, especially in developing countries, which is probably due to a combination of genetic and environmental factors.

Children

Asthma is the most common chronic disease of children in Australia. It accounts for a significant proportion of acute hospital admissions and absent days from school. However, despite its frequency, there is no clear definition of asthma in children.

It is difficult to determine the rates of asthma in children because many children will experience symptoms of cough and wheeze which is not necessarily asthma. Doctors may be cautious in giving your child the label of asthma as this may mean other diseases of the airways may be overlooked.

Most children with wheeze will not have asthma or any significant disease. Wheeze in young children is commonly caused by viruses (e.g. cold or flu), which induce wheezing due to the immaturity of the airways.

Realtime Health Video

Watch a video on Childhood Asthma: Diagnosis and Acceptance

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Predisposing Factors

The cause of asthma remains unknown. It is likely that people develop asthma as a result of a complex interaction between genes, which are inherited from your parents, and environmental factors, which are not fully understood.

One theory for this is that in developed countries we have become too clean and children are no longer exposed to enough germs, which makes them more likely to develop allergic diseases such as asthma. This theory is known in scientific circles as the Hygiene Hypothesis.

The tendency for people to be allergic is known as atopy. You are atopic if you react to allergens in tests (e.g. a skin prick test). People who are atopic may have no symptoms, or they may have symptoms of allergic disease such as eczema, hayfever or allergic asthma. It is known that people with allergies are more likely to develop asthma. 90% of children and 50% of adults with asthma are atopic.

People with a family history of asthma or allergy are more likely to develop asthma than people with no family history of asthma or allergy. Other factors that increase the risk of developing asthma include exposure to smoking during pregnancy or exposure to cigarette smoke in early childhood, and living in developed countries. Occupational asthma can result from exposure to certain chemicals and irritants at work. Research is continuing to help identify factors that cause asthma and ways to prevent asthma from developing in people who are at risk of developing asthma.

Currently the only firm recommendations to help prevent asthma in children include:

Exclusively breastfeed your child for 6 months. If you are unable to breastfeed or don't want to, use a partially hydrolysed formula for this period. Ask your doctor or pharmacist about appropriate brands of formula.
Avoid smoking and smoke exposure during pregnancy and infancy.

In people with asthma, attacks can be triggered by exposure to allergens, including dust mites, animal fur (e.g. cats, dogs and horses), grass pollens, mould, viral infections such as the common cold, exposure to cold air, exercise, acute emotions such as laughter or crying, and various irritants such as chlorine bleach. The most common triggers of acute asthma attacks in children are viral infections such as the common cold.

Different people have different triggers for their asthma. What triggers asthma in one person may not trigger asthma in another person. Ask your doctor for advice on what is likely to trigger your asthma and how to avoid your triggers. Note that identification of allergens and avoidance can be difficult, particularly in children, in whom most attacks are due to viruses.

Progression

While some children do 'grow out' of their asthma, the tendency for sensitive airways often remains, and it is important to remain vigilant for signs of the disease re-emerging. It is often not possible to predict whether asthma is likely to get worse or better in the future, but it is known that children with allergic asthma are less likely to fully 'grow out' of their asthma, though it may improve with age. Children with earlier and more severe disease and a family history of asthma are more likely to find their asthma persisting into adult years.

Asthma in children is sometimes classified more specifically into three main groups:

Infrequent episodic (intermittent) asthma: Most children (70-75%) have this type of asthma. They have only a few exacerbations per year, often associated with viral infections. In between episodes they are completely well. The asthma tends to resolve with age.
Frequent episodic (intermittent) asthma: Children in this category (20%) have shorter intervals between exacerbations and may have 6 or more attacks per year. They may also have some mild symptoms between episodes and will benefit from preventer medications.
Persistent asthma: These patients (5-10%) have symptoms on most days and require more intensive therapy.

Asthma can also occur for the first time in adults, where it is often not triggered by allergens. It may be work related, and symptoms triggered by allergens, chemicals or irritants in the workplace. Some people get asthma that is made worse by medications such as aspirin and other non-steroidal anti-inflammatory drugs.

Ask your doctor if you need to be careful about what painkillers you take if you are concerned that they may be triggering your asthma.

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