Filtered diesel exhausts may worsen allergies, study finds

Air pollution from supposedly ‘safer’ diesel exhausts may worsen allergy-induced lung problems, according to new research.

A diesel particulate filter (DPF) captures and stores exhaust soot in order to reduce emissions from diesel cars, and is legally required to prevent the emission of high levels of particulates.

However, the research, which is published in American Thoracic Society’s American Journal of Respiratory and Critical Care Medicine, reports that exposure for people suffering from allergies increases.

The study looked at 14 adults who were sensitive to at least one of three common allergens.

Participants at various times were exposed in a laboratory to air with just the allergen, the allergen plus diesel exhaust and the allergen plus filtered diesel exhaust. They all also breathed air with no diesel exhaust or allergen, which served as the control.

After each exposure, the participants underwent a commonly used test called ‘methacholine challenge’ to determine how a patient responds to an inhaled allergen. Neither they nor those conducting the study were aware of which exposure they had undergone before being tested.

The study found the particle-depleted diesel exhaust produced by filtration generated higher NO2 levels than unfiltered diesel exhaust.

The researchers also measured numbers of white blood cells, which look after the body’s immune response but can ‘overreact’ to allergens, causing breathing problems.

Exposure to filtered diesel exhaust and allergen also impaired the number of air participants could forcibly exhale in one second, which suggests that white blood cells play a meaningful role in reducing lung function during exposure to air pollution.

‘The take-home message,’ said senior study author Professor Chris Carlsten, ‘is that technologies that remove particulate matter from diesel exhaust cannot be simply assumed to be beneficial to health, especially in susceptible populations.’