Asthma is a chronic inflammation of the respiratory tract (bronchi). The respiratory tract is hypersensitive to certain stimuli and thereby constrict. These stimuli can be caused by seemingly harmless substances (e.g. pollen, fruit, and nuts), psychological stress, or overexertion. This results in paroxysmal dyspnoea, coughing, expectoration, and wheezing during exhalation. In recent decades, the prevalence of asthma has significantly increased in most countries – especially the industrialised ones. The exact causes are still unknown. Allergies (e.g. hay fever), dermatitis, and a family history of asthma are all important risk factors for asthma. Environmental factors (e.g. cigarette smoke and air pollution) and frequent viral infections can also trigger asthma in susceptible individuals.
There are three different forms of asthma. In allergic asthma, the symptoms are triggered by allergens such as pollen, house dust, or animal hair. Typical triggers for non-allergic asthma include physical stress, extreme temperature fluctuations in the breathing air, and tobacco smoke. In mixed forms, asthma attacks can be triggered by both allergic and non-allergic factors.