Scientists and the public have long known the damage air pollution does to our lungs and our hearts.
Now, scientists are beginning to assess the effects on our largest organ - our skin.
They have fingered ozone and fine particulates as the likely worst culprits, and are finding that they may cause dark spots, inflammation, a lack of hydration, and premature aging.
So far, we know this information mainly from skin-care companies. Yes, that makes it somewhat suspect, given the potential financial gains from a whole new array of skin-care products, many of them likely expensive.
Indeed, one industry executive told the Wall Street Journal, "We believe that pollution is the next UV," referring to ultraviolet rays from the sun and the plethora of sunscreen products that have resulted.
But it's hardly surprising - or new - that the marketplace produces the initial research.
Sadly, many things in addition to the mere passage of time can cause the skin to age. They include exposure to the sun, smoking, and even stress. But all apparently damage us in slightly different ways, and although we know plenty about how the sun ages the skin, we don't know as much about how pollution does it.
Some of the early work has been done in Beijing, which became notorious for its air pollution during the 2008 summer Olympics there.
Olay studied the skin health of 200 women and found that - all other things being equal - those living in high pollution areas, as opposed to those living in suburbs with cleaner air, had significantly worse skin hydration. They also found lower levels of biomarkers related to the skin's barrier function.
Olay senior scientist Frauke Neuser said in a news release "the evidence shows that it is vital for skin care today to incorporate pollution-fighting, skin-repairing ingredients."
Olay has been doing that. In January, it released three new moisturizers in its "Total Effects" line, formulated with 40 percent more vitamins and increased amounts of niacinamide, a form of Vitamin B3 - all aimed, at least in part, at blunting the effects of pollution, although online product descriptions don't specifically mention antipollution properties.
And there are more:
Clarins offers a UV Plus Anti-Pollution sunscreen. For $42, it will help "screen out harsh environmental influences that contribute to premature signs of aging," the company promises.
Dior's Nude Air powder ($54) "unifies and mattifies the complexion while acting as a veritable shield against pollution, to allow the skin to breathe freely," the company says.
SkinCeuticals' CE Ferulic serum ($162) "delivers advanced environmental protection," the company says.
Notice how vague the claims are? That's likely to keep the products within the category of "cosmetics," which do not have to be approved by the U.S. Food and Drug Administration before going on the market. If the product is aimed at affecting "the structure or function of the body," the FDA says - if it's intended to remove wrinkles or increase the skin's production of collagen - it's a drug or medical device and is subject to more rigorous review.
Products marketed in Europe and elsewhere seem to make more specific claims - such as Lancôme's "City Miracle" cream, "tested in some of the world's polluted cities and recognized by women to help protect against daily aggressions." The product does not appear on Lancôme's U.S. website.
The Clarisonic skin-cleansing brush, though not new, is branching out to the air-pollution realm. Company studies show the brush is 30 times better at removing "age-accelerating pollution" than manual cleansing, the website says. An infographic warns, "don't let pollution stand in the way of healthy skin."
Expect even more products, says Mintel, a global market research firm, in its 2015 consumer trends report. Focusing on Europe, the company said that after dust smog from the Sahara swept across England in 2014, interest in antipollution products was expected to grow.
But is all this really true? Which products, if any, work, and which don't?
Clearly, this is an emerging field. Neither the University of Pennsylvania Health System nor the Temple University Health System were able to produce experts to comment.
Last year, experts from Europe and Asia - including physicians, dermatologists, and researchers for the cosmetics company L'Oreal - formed a panel to study the research so far. Their review paper was published in November by the Journal of Dermatological Science. The researchers said the first study to indicate particulates were harmful was produced in 2010, when researchers found women in Germany who lived closer to specific pollution sources (traffic and the steel and coal industries) had "extrinsic skin aging."
They're not sure how all this works just yet, but researchers think air pollution can alter the skin barrier and damage skin cells. That may be especially true of particulates, which have other harmful chemicals attached and appear to be able to penetrate the skin.
The panel concluded the published research so far indicated "it is indeed possible to develop specific cosmetic/cosmeceutical strategies to counteract pollution-induced skin damage." And that - eureka! - doing so would be "highly desirable."
Meanwhile, they recommended general measures to protect the skin:
Use rinse-off products such as shampoos and shower gel to clean pollution from the skin.
Still, avoid overwashing the skin, which could damage its natural protective barrier.
Protect the skin with foundation or BB creams.
Use sunscreen so the compounds in air pollution that react to light won't be activated.
Use emollients to preserve and restore the skin-barrier function.