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Whether you’re indoors or out, your skin is affected by the environment.

From UV rays to blue light and pollution, “all these environmental factors work by creating oxidative damage in the skin, which breaks down collagen and may also serve to damage the barrier function of the skin. A damaged barrier makes skin more prone to the ill effects of UV damage,” says Jennifer Chwalek, MD, a dermatologist at Union Square Laser Dermatology in New York City.

Oxidative damage or stress happens when the level of harmful free radicals present surpasses that of the neutralizing “good guy” antioxidants, according to an article published in Polyphenols in Human Health and Disease in 2014.

UV Rays Are the Most Significant Threat to Skin

First up: the sun. “UV radiation is the most significant environmental factor and also one of the most recognized when it comes to skin damage and aging,” says Marisa Garshick, MD, a dermatologist at Medical Dermatology and Cosmetic Surgery in New York City.

UV rays trigger the production of free radicals in the skin that lead to DNA damage and the breakdown of collagen and elastin in the skin, causing wrinkles, notes the World Health Organization (WHO); it also stimulates the melanin production that leads to skin discolorations, says Garshick. According to a 2017 article in Tropical Dermatology, melanin is a pigment that gives skin its color. Beyond aesthetics is the increased risk of skin cancers. It’s the cumulative effect of sun exposure that, over time, can lead to the formation of non-melanoma skin cancers, including basal cell carcinoma (BCC) and squamous cell carcinoma (SCC); early childhood UV exposure may be a bigger factor in melanoma skin cancers, which can be deadly, the WHO points out.

The Sun Isn’t the Only Skin Scourge

Blue light or visible light is one potential skin ager that experts are increasingly wary of. “Blue light lies on the visible light spectrum. It is high-energy wavelength light that comes from our computer screens and phones,” says Garshick. While research is still emerging and studies tend to be very small, some suggest that keeping your face stuck in a screen all day could also lead to premature aging.

For example, one study published in Oxidative Medicine and Cellular Longevity in February 2015 suggested that visible light increased free radical formation in the skin. Another, in the December 2018 issue of the Journal of Biomedical Physics Engineering suggests that this free-radical-generating light also includes the flash on smartphones. (The title even asks if taking selfies can lead to premature aging.)

Air Pollution Plays a Role in Accelerating Skin Aging

Air pollution doesn’t just affect how you breathe. As the U.S. Environmental Protection Agency (EPA) warns, it can also create the same free radical damage in skin as light. “Exposure to air pollution, which includes particulate matter, nitrogen dioxide, hydrocarbons, and ozone, creates oxidative damage in the skin that increases inflammation,” says Dr. Chwalek, whose statement is supported by data cited in a review published in Dermato-Endocrinology.

Consider particulate matter (PM), for instance. PM is a mixture of small particles and liquid droplets, such as organic chemicals and soil or dust, according to the EPA. A study on human skin cell cultures published in September 2018 in the International Journal of Molecular Sciences suggests that PM stimulates skin inflammation and impairs collagen synthesis.

Over time, this may cause sagging and fine lines and wrinkles. “Pollution creates the free radicals in skin that prematurely chew up collagen and elastin,” says Rebecca Kazin, MD, an associate director at the Washington Institute of Dermatological Laser Surgery in Chevy Chase, Maryland.

What’s more, if you’re dealing with dark spots appearing on your face, you may have cars to blame. An article published in May 2016 in the Journal of Investigative Dermatology also shows that exposure to air particles from traffic is linked to pigment spots on cheeks, Garshick points out.