Grass pollen and the fall in temperature seem to be to blame

Despite its increasing prevalence, the aetiology of asthma remains mysterious. However, a panoply of factors continues to be associated with acute episodes of asthma. In recent years, environmental epidemiologists have conducted numerous studies investigating the relations between indoor and outdoor air pollutants and asthma, particularly focusing on exposures to ozone, sulphur dioxide, nitrogen dioxide, and particulate matter of respirable diameter. Researchers have found it difficult to standardise measures of exposure, and most have used an ecological design, searching for associations between exposures measured in environments and outcomes measured in individuals (typically asthma attacks or health care utilisation). Despite the large amount of research, the evidence that air pollution causes asthma remains controversial.1

Research into the causes of chronic diseases, such as asthma, seldom produces the immediate gratification of the epidemic curve seen in acute infectious disease, which can then …