The levels of traffic-related air pollution and air pollution-associated gases are linked to the formation of dark spots on the skin, a new study has found.
The most pronounced changes were observed on the cheeks of Asian women over the age of 50, researchers said.
"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.
"While NO2 exposure is known to be associated with low lung function and lung cancer, the effect of NO2 on human skin has never been investigated," said Krutmann.
"This is important because environmentally-induced lung and skin ageing appear to be closely related," she said.
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 average age was 73.5 years (range 67 to 80 years) and 20 per cent had a history of smoking. These women reportedly spent an average of 2.6 hours a day in the sun.
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).
Twenty per cent of this group had a history of smoking, with a reported average daily sun exposure of 3.5 hours.
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.
Overall, an increase of 10 microgrammes per cubic metre in NO2 concentration was associated with approximately 25 per cent more dark spots.
The researchers performed sensitivity analysis and found that the NO2 gas had a slightly stronger effect than the particulate matter concentration.
Lentigenes, also known as liver spots, are small, darkened areas of the skin. Although they may first appear small, they may enlarge and separate patches may merge. They are most commonly found on the face, forearms, hands, and upper trunk.
Usually brown in colour, lentigenes can appear yellow-tan to black. They are more common in light-skinned individuals and in US, solar (sun-associated) lentigenes are noted in 90 per cent of Caucasians older than 60 and 20 per cent of those younger than 35 years.
Lentigenes, which contain an increased number of the melanin-forming cells of the skin (melanocytes), are generally benign, although some forms may be pre-cancerous.
The study was published in the Journal of Investigative Dermatology.
