Abstract Background Propionibacterium acnes ( P. acnes ) has been implicated in the inflammatory phase of acne vulgaris. It has been shown to activate interleukin-8 (IL-8) secretion by interacting with Toll-like receptor 2 (TLR-2) on the surface of keratinocytes. Nicotinamide has been shown to be an effective treatment for skin inflammation in various conditions, including acne vulgaris. Objective To investigate the molecular mechanisms underlying the anti-inflammatory properties of nicotinamide in keratinocytes stimulated by P. acnes. Methods HaCaT cells and primary keratinocyte cell lines were stimulated by P. acnes in the presence of nicotinamide. IL-8 production was monitored by ELISA on the cell culture supernatant and by qRT-PCR on total RNA extract. A luciferase reporter system assay was used to assess nicotinamide activity with the IL-8 promoter in transfected keratinocytes. We used western blotting to analyze the effect of nicotinamide on activation of the NF-κB and MAPK pathways. Results Nicotinamide significantly decreased IL-8 production in a dose-dependent manner, decreasing both mRNA and protein levels for this chemokine in immortalized HaCaT cells and primary keratinocytes. P. acnes -induced IL-8 promoter activation seemed to be downregulated by nicotinamide, which inhibited IκB degradation and the phosphorylation of ERK and JNK MAP kinases. Conclusion Our results indicate that nicotinamide inhibits IL-8 production through the NF-κB and MAPK pathways in an in vitro keratinocytes/ P. acnes model of inflammation. Keratinocytes involved in the innate immune response may be a suitable target for treatment during the early phase of inflammation.