Older women often struggle to control dark spots, because no matter what product they use, these spots would not go away. In a new study, researchers found the link between traffic-related air pollution and the formation of facial dark spots in women.

The study, published in the Journal of Investigative Dermatology, included women from Germany and China to demonstrate the link between the levels of traffic-related gas emissions and the formation of dark spots known as lentigines on the skin

They found that Asian women older than 50 years old usually had the most pronounced changes on their cheeks. Aside from particulate matter, air pollution contains increased amounts of nitrogen dioxide (NO2), which has been linked to the development of health conditions like lung diseases and cardiovascular problems. Its effect on the skin, however, has never been investigated, the researchers said.

With an aim to demonstrate the link, the researchers studied two groups of women. The first group involved 806 Caucasian German women and the second group included 743 Han Chinese women. The first group had 2.6 hours a day exposed to the sun while the other group had 3.5 hours. In terms of smoking, about 20 percent of both groups had done the habit.

For the levels of NO2 exposure, the German women had 28.8 micrograms per cubic meter (µg/m3) and the Chinese group had 24.1 µg/m3.

The researchers found no link between the levels of NO2 and formation of lentigines on the forearms and back of the hands, but they noted the increased formation on the cheeks in both groups.

"To the best of our knowledge, this is the largest epidemiological study demonstrating a link between traffic-related air pollution and the formation of lentigines," the study says (PDF).

An increase of 10 µg/m3 NO2 concentration was linked to 25 percent increase in dark spots. The researchers also performed sensitivity analysis and unveiled that the NO2 gas had a stronger effect than particulate matter concentration.

"The findings also strengthen the concept that the pathogenesis of lentigines might differ depending on the anatomical site," Li Jin, Ph.D., from the Fudan University's State Key Laboratory of Genetic Engineering, said.

Lentigines are benign lesions that usually occur on sun-exposed parts of the body. The number and size of the dark spots usually increase with age. They are most commonly found on the face, forearms, hands, and upper trunk.

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