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Epidemiological studies have shown that cigarette smoke (CS), a very common environmental factor, plays an important role in skin aging.Although some in vivo studies have suggested that CS affects skin aging, the detailed effects of CS on skin cells in vitro remain largely unknown.In this study,we investigated the effects of cigarette smoke extract (CSE) on the growth, proliferation, and senescene of skin fibroblasts and the possible mechanism underlying these effects.Primary cultured human fibroblasts were exposed to a range of concentrations of CSE.Cell viability and cell proliferation after CSE exposure were analyzed with the methyl thiazolyl tetrazolium (MTT) assay and bromodeoxyuridine incorporation assay, respectively.Growth curves of fibroblasts exposed to different concentrations of CSE were developed and prolonged CSE-exposed cells were observed.Morphological and ultrastructural changes in fibro blasts were assessed by inverted light microscopy and transmission electron microscopy (TEM).Dying cells were stained with senescence-associated β-galactosidase (SA β-gal).Intracellular reactive oxygen species (ROS) levels, superoxide dismutase (SOD) activity, and glutathione peroxidase (GSH-Px) activity were determined by a colorimetric method.We found that proliferative capacity and growth were inhibited by CSE exposure in a dose-and time-dependent manner.Fibroblasts exposed to even low concentrations of CSE for a long period of time (5 passages) showed significantly increased SA β-gal activity and typical features of aging cells.Meanwhile, CSE inhibited superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities and augmented ROS levels.Our observations suggest that CSE exposure impairs fibroblast growth and proliferation and leads to features similar to those seen in senescent cells.Oxidative stress injury and inhibition of antioxidant defense activity may be involved in CSE induced fibroblast senes cence.