Women with the most beautiful skin spend lots of time in the country and not in the soot and grime of Beijing—that’s the news from Professor Wei Liu, a dermatologist at the China Air Force general hospital in Beijing.

Read: New Skin

The professor, whose scientific work was funded by Procter & Gamble, says 224 chemicals in urban pollution damage skin keratin, a type of protein that prevents dehydration, leading to deficient collagen production and premature wrinkles and lines.

The study used 200 women between 30 and 45 with similar lifestyles and sun exposure. Country women could’ve used more sunscreen because they had some sunlight-related aging but damage was far worse in city dwellers—by about 10%, according to the P&G study.

Procter & Gamble scientific spokesperson Frauke Neuser says: “In the past it was believed toxic particles in urban dust may stick to the face, but are too large to penetrate skin. We now know particles as small as 0.1 of a micrometer, many times smaller than a grain of sand, carry a variety of these toxins and can get below the skin.”