Supplementary Materials: The following supporting information can be downloaded at: www.mdpi.com/xxx/s1, Figure S1: Phenformin but not metformin suppresses the skin acute inflammatory response induced by TPA; Figure S2: Phenformin reduces the ear thickness increased by TPA treatment; Figure S3: Phenformin reduces the infiltration of immune cells induced by TPA treatment in the dermis; Figure S4: List of the Top 20 enriched Hallmark pathways from GSEA analysis; Figure S5: Phenformin suppresses c-Myc expression induced by either Poly (I:C) or TPA in keratinocytes; Figure S6. The c-Myc inhibitor JQ1 suppresses skin acute inflammatory responses induced by TPA treatment; Figure S7: The c-Myc inhibitor JQ1 decreases the infiltration of immune cells induced by TPA treatment in the dermis; Figure S8: Phenformin suppresses pro-inflammatory cytokine expression induced by Poly (I:C) in dermal fibroblasts; Table S1: Oligo primer sequences used for RT-PCR analysis, Table S2: siRNA sequences used in this study.