"In addition to particulate matter, traffic-related air pollution is characterised by increased concentration of nitrogen dioxide (NO2)," said lead investigator Jean Krutmann, of the IUF-Leibniz Research Institute for Environmental Medicine in Germany.

Two groups were studied. The first included 806 Caucasian German women who were part of the SALIA study (Study on the influence of Air pollution on Lung function, Inflammation and Ageing). The second group included 743 Han Chinese women from the Taizhou region who were younger than the SALIA group, with an average age of 59 (range 28 to 70 years).

The mean levels of NO2 exposure were 28.8 microgrammes per cubic metre in the SALIA study and 24.1 microgrammes per cubic metre in the Taizhou China group. No link was seen between levels of NO2 and formation of dark spots called lentigenes on the back of the hands or forearms, however, exposure to NO2 was significantly associated with more lentigenes on the cheeks in both German and Chinese women older than 50 years.

The researchers performed sensitivity analysis and found that the NO2 gas had a slightly stronger effect than the particulate matter concentration.

The study was published in the Journal of Investigative Dermatology.

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