Controlled full-body human exposure to ozone increases malondialdehyde on skin

Malondialdehyde (MDA), a product of lipid peroxidation, is a biomarker of oxidative stress. We investigated the relationship between ozone exposure and MDA in skin wipes in a series of three controlled full-body chamber studies. Twenty-nine volunteers were exposed under different levels of temperature, relative humidity, ozone concentration, clothing coverage, and ventilation rate. One study also examined age-related differences among teenagers, young adults, and seniors. Exposures lasted between 3 and 6 hours. Skin wipes were collected from the volunteers' forearms before and after exposure and analyzed for MDA and, in some cases, squalene. To characterize baseline variability, skin wipes were collected from 3 unexposed reference persons twice a day for 5 days. Two skin wipes were collected daily from two additional persons; one from each person was subsequently exposed to chamber air, the other was unexposed. This was to distinguish ozone chemistry on collected skin oil from processes occurring directly on skin. Ozone exposure significantly increased MDA on skin. A higher post/pre-exposure MDA ratio was observed with a longer exposure duration. MDA concentrations were an order of magnitude higher on skin-oil-loaded wipes exposed to ozone than on wipes collected from volunteers exposed to ozone. This suggests that ozone reactions with skin lipids can generate MDA even in the absence of an inflammatory process. Inter- and intra-person variability in skin MDA can be attributed to the combined influence of environmental and personal factors, which drive the production and transformation/uptake of MDA on skin. The lack of association between squalene depletion and MDA production suggests an intricate balance between parallel, possibly interconnected, ozone-initiated formation and loss mechanisms responsible for the measured concentrations of the two compounds.