SFRP2 and freckles: Similarly, ET-1 in SL [67], HGF in DF [69]/SL [14], KGF in SL [22,68,70]/melasma [70], IL-1α in SL [22], sFRP-2 in SL [24,71]/melasma [24], and NGF in melasma [66] stimulate melanogenesis of human melanocytes.