Dark spots may not just be a sign of aging. A largescale study of women from Germany and China demonstrated a link between levels air pollution with the formation of dark spots on the skin, known as lentigenes or liver spots. The most pronounced changes were observed on the cheeks of Asian women age 50 and older. The researchers measured the levels of nitrogen dioxide (NO2) exposure and number of lentigenes and published findings in the Journal of Investigative Dermatology. "In addition to particulate matter, traffic-related air pollution is characterized by increased concentration of NO2,” says lead investigator Jean Krutmann, M.D., of the IUF-Leibniz Research Institute for Environmental Medicine (Dusseldorf, 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. This is important because environmentally induced lung and skin aging appear to be closely related."
Researchers studied two groups, 806 Caucasian German women who spent an average of 2.6 hours per day in the sun and 743 Han Chinese women from the Taizhou region with a reported average daily sun exposure of 3.5 hours. For women older than 50 in both groups, exposure to NO2 was significantly associated with more lentigenes on the cheeks, but not on hands or forearms. Overall, an increase of 10 µg/m3 in NO2 concentration was linked with approximately 25 percent more dark spots. The spots were visually evaluated by trained personnel according to photo reference scales and quantified using a validated skin aging score system (SCINEXA).
The investigators performed sensitivity analysis to pinpoint whether it was the concentration of particulate matter or NO2 gas that had a greater impact on dark spot formation. They found that the NO2 gas had a slightly stronger effect than the particulate matter concentration. "To the best of our knowledge, this is the largest epidemiological study demonstrating a link between traffic-related air pollution and the formation of lentigenes," says co-investigator Li Jin, Ph.D., of Fudan University's State Key Laboratory of Genetic Engineering and Ministry of Education Key Laboratory of Contemporary Anthropology, Collaborative Innovation Center for Genetics and Development, School of Life Sciences (Shanghai) and the Fudan-Taizhou Institute of Health Sciences (Taizhou, Jiangsu, China). "The findings also strengthen the concept that the pathogenesis of lentigenes might differ depending on the anatomical site."—Jennifer Nied