Health
The exact cause of asthma isn't clear but a combination of genetic predisposition and environmental influences can lead to increased reactivity of the airways. These influences include atopy - an inherited tendency to allergic disease including eczema, hay fever and other types of allergic rhinitis.
Cells and chemicals from the immune system enter the lung tissues and the breathing tubes become hyper-reactive. This means the tubes are easily triggered into constricting or narrowing, making it harder to move air through the lungs, and breathing becomes difficult.
Once the airways are hyper-reactive, a variety of triggers cause the sensitised lungs to react, leading to an asthma attack.
Triggers include respiratory tract infections, allergens (particles that cause an allergic response, such as house dust mite droppings or pollen), smoking, exercise, cold air, emotional upsets and chemical irritants.
Coughing (often at night), wheezing, a tight feeling in the chest and shortness of breath are common. These symptoms occur intermittently and vary in severity from day to day.
Some people have mild symptoms that affect them only occasionally, while others have severe symptoms that need treatment in hospital. Symptoms tend to be worse at night and first thing in the morning.
In preschool children, the main symptom may be a troublesome night-time cough. There may be symptoms of other atopic conditions, such as eczema.
Asthma can affect anyone, at any age, anywhere, but it is particularly common among children.
Asthma can run in families and is more likely to develop if someone already has eczema or hay fever. The chance of a child developing asthma is reduced if the mother doesn't smoke in pregnancy and the child isn't exposed to passive smoking.
Diagnosis is made on the basis of symptoms along with investigations such as a chest x-ray and, importantly, lung function tests.
Diagnosis can be more difficult in younger children
In over-fives, the most useful test is one that measures the peak expiratory flow rate (PEFR or peak flow - a measure of how fast air can be pushed out of the lungs). Diagnosis can be more difficult in younger children, where other conditions often cause wheezing.
Treatment includes medication usually given straight to the lungs through inhalers or other devices, and consists of relievers (bronchodilators) to open restricted airways, and preventers (steroids and other drugs) to prevent asthma attacks.
It's important to have a written self-management plan advising how to use treatments and what to do if these aren't controlling asthma symptoms, and to attend regular asthma check-ups.
The risk of an attack is reduced by not smoking and avoiding identified asthma triggers, such as house dust mite droppings, pet hairs, smog and stress, as much as possible. Coughs and colds also trigger asthma symptoms.
The chance of a child developing asthma is reduced if the mother doesn't smoke in pregnancy and if the child isn't exposed to passive smoking.
People with asthma shouldn't avoid exercise.