Acne vulgaris is a chronic inflammatory disease of the pilosebaceous units (PSU). Light therapy has attracted medical interest as a safe, alternative treatment for acne. Both blue and red light therapies at high doses >10 J/cm 2 have demonstrated marked effects on inflammatory acne lesions. However, few studies have investigated the effects of lower doses of light. In this study, the biological effects of low red light doses were investigated using an in vitro model previously developed to mimic the inflammation, and hyperkeratinization seen clinically in acne. Human epidermal equivalents were topically exposed to an unsaturated fatty acid, oleic acid (OA), which is elevated in skin of acne patients, followed by red light treatment once per day for two days. Skin inflammation was monitored by evaluation of the proinflammatory cytokine, IL-α. Furthermore, stratum corneum thickness was studied to evaluate the hyperkeratinization response to OA. The supernatants were collected at day 2 for enzyme-linked immunosorbent assay (ELISA) for evaluation of IL-1α and the tissues were collected for histologic examination. OA-induced IL-1α release was significantly reduced from 266 ± 11 pg/mL for non-light-treated controls to 216 ± 9 pg/mL, 231 ± 8 pg/mL and 212 ± 7 pg/mL, respectively following red light treatments at 0.2 J/cm 2, 0.5 J/cm 2, and 1.2 J/cm 2 ( P < .05). Histologic examination showed that stratum corneum thickening following OA treatment was reduced from 43% of total epidermis for no light treatment to 38% following light treatment ( P < .05). Taken together, these results suggest that low energy red light phototherapy could provide beneficial effects on unsaturated fatty acid-induced inflammation and hypkeratinization for acne vulgaris.