Asthma: introduction and risk factors
Asthma is a chronic disease of the small airways in the lung. Airway inflammation and associated bronchoconstriction leads to recurrent attacks of cough, wheezing, breathlessness or chest tightness. The severity and frequency of these episodes varies from occasional slight wheezing to severe or sometimes, although rarely, life-threatening attacks.
Asthma is common in Scotland and internationally, with approximately 262 million people affected worldwide in 2019 (according to the World Health Organisation). It tends to be under-diagnosed, indicating official figures may be an underestimate. The annual mortality associated with asthma in Scotland is relatively low; however, asthma reduces the quality of life of sufferers, demands regular treatment, and is presently incurable.
Risk factors
The underlying causes of asthma are not fully understood, but attacks are likely caused by an interaction between a susceptible host and environmental triggers.
There are a wider range of potential environmental triggers, which include exposure to house dust mites, pollen, animal hair, certain foods, viral infections, moulds, fungi and environmental tobacco smoke. Avoidance of these triggers may help to control asthma.
Genetic factors are likely to contribute to the hypersensitive state of the airways of asthma sufferers, where family history is a risk factor. Some genetic variants may also cause asthma only when combined with certain environmental exposures.
A number of other factors have been explored as potential explanations of increase in the risk of asthma, including exposure to infections in early life, indoor and outdoor pollution, environmental tobacco smoke, diet and drug use, obesity, rates of caesarean sections, and breast feeding. The hygiene hypothesis suggests that lower levels of exposure to childhood infections increases the risk of asthma. However, none of these explanations fully explain the rise in prevalence of asthma that has been seen in some countries.
