involved in skin damage caused by pollutants can also differ from the mechanisms involved in UV damage. Understanding the specific mechanisms responsible for the damage associated with each pollutant is vital to properly plan a good defensive strategy for limiting their damage.
An example is represented by ozone, tropospheric levels of which have increased considerably over recent decades, particularly in major metropolitan areas.3 While UV light is able to induce tissue damage by penetrating the skin, ozone cannot penetrate the skin and its effect is limited to interaction with the stratum corneum. Continuous exposure of the skin to high levels of ozone results in the accumulation of peroxidation products and induction of stress responses in the active layers of the skin, most likely due to indirect mechanisms.3 In addition to its role in accelerating skin damage associated with aging, exposure to high levels of ozone is associated with urticaria, contact dermatitis, rash, and skin infections.5
Exposure to ambient particulate matter (PM) has been associated with several pathologic conditions and can impact the structure and functionality of many organs, including the heart and lungs.8 There is also clear evidence that PM can accelerate skin aging, increase cutaneous spots, and induce skin inflammation.3,9
Currently, it is not known whether PM can pass through the skin. It has been suggested that some PM may enter the lower layers of the skin through hair follicles. Alternatively, rather than being permeated by the whole particle, the skin may absorb certain molecules that are attached to the particle. For example, aromatic compounds can be absorbed because they are lipid soluble and, once inside the skin, they induce inflammation.10,11
Nevertheless, regardless of whether PM enters the skin, evidence of its harmful effects is unequivocal.12 Elevated levels of PM have been found to correlate with clinic and emergency department visits for urticaria.13,14 Clear data shows that living in an urban area
