Human skin is constantly assaulted by the external environment, protecting us from air, Ultraviolet radiation (UVR), environmental pollutants, and other mechanical and chemical insults, all of which have been piled into the coined term "exposome," to describe the entirety of exposures to which an individual is subjected. The skin's ability to protect us can be easily impaired by numerous factors such as psychological stress, alcohol and illicit drug intake, and poor nutrition, all of which further allow external factors to do harm by creating free radicals such as reactive oxygen species (ROS). Now truth be told, the greatest focus is often on UVR, which is the major contributor to this injury. Our skin can combat UVR through both its inherent protective tools(melanin, urocanic acid, and enzymatic antioxidants) and antioxidants we consume from the food (vitamin A, C, E, etc.), but these can be depleted with use and age, not to mention other environmental villains like pollution. In fact, a very recent study indicates that exposure to increased ground levels of ozone for example, may be associated with increase wrinkle formation in the face, even independent of sun exposure. When I say ozone, I am not referring to stratospheric ozone in the upper atmosphere that is beneficial because it protects from solar radiation. Ground level or tropospheric ozone is the accumulation of gaseous emissions from cars and chemical plants. Nitrogen oxide and organic compounds in these emissions interact with sunlight to become highly reactive (not a good thing). Although we often think of ground ozone in association with large cities or industrial areas the reality is that many Americans live in areas with unhealthy levels of ozone.
The skin is, of course, exposed to this ground level ozone, and there is growing evidence that confirms that this exposure has detrimental effects on the skin such as premature skin aging and increased sensitivity . Regular contact with ozone depletes antioxidants from the stratum corneum, the top layer of the skin . Ozone also increases damage to key fats and proteins in the skin, called lipid peroxidation and protein oxidation respectively, suggesting multiple way by which ozone and even soot (a mixture of carbon particles and organic compounds such as polyaromatic hydrocarbons ) we come into contact on a daily basis can 1. Damage our skin and 2. Further facilitate the damage incurred by UVR exposure by depleting out defenses. Overall, there is good epidemiological evidence that exposure to traffic-related air pollution including such as Nitrogen Dioxide and ground level ozone as well as cigarette smoke is associated with increased pigment spots and wrinkle formation, aka accelerated skin aging, in multiple ethnicities such as Caucasians and East Asians.
So what to do about this? Well first things first, we must continue to be vigilant with proper sunprotection regiments which include:
1. Applying a SPF 30 or higher sunscreen, with or without antioxidants, to exposed areas every single day. Specific to this discussion, it will also prevent sunreactive pollutants from reacting upon UV exposure.
2. Reapply after bathing, swimming, exercising, or if outdoors for extended periods of time
3. Use protective clothing such as hats and sunglasses as sunscreen is not enough
4. Seek shade when possible
5. Don't assume windows protect - they only filter one half of the story, UVB, but lets UVA, the type that does not cause a clinical sun burn but sure burns your DNA, have at your skin.
What about the pollution? Good question. Here's where we need to rely on our friends in industry to create mutli-functional products that can both protect us form the sun and pollution. In the meantime, strategies to reduce pollution particle load on the skin are helpful. These include the use of rinse-off products to remove pollution from the skin and 'anti- stick' topical products which make particles slip off the skin. It is still important to avoid over cleansing which can further disrupt the skin barrier. Second, the use of moisturizers to preserve and restore skin barrier function will help prevent additional damage and exposure to harmful pollutants.