In experiments with keloid fibroblasts and normal cutaneous fibroblasts stimulated by transforming growth factor-β1, the administration of exogenous H2S reduced the levels of several key markers, including α-smooth muscle actin (α-SMA), proliferating cell nuclear antigen (PCNA), collagen type I, collagen type III and anion superoxide. The gene discussed is PCNA; the disease is keloid.