“…Proopiomelanocortin-derived β-endorphin, one of their endogenous ligands (Bigliardi-Qi et al ., 2000, 2004; Kauser et al ., 2003, 2004; Tobin, 2006), is locally produced in the skin (Slominski et al ., 1992, 1993; Furkert et al ., 1997; Slominski, 1998) and stimulates epidermal and follicular melanogenesis (Kauser et al ., 2003, 2004). Although there are reports demonstrating the presence of Met-enkephalin antigen in adult mammalian skin (Weihe et al ., 1983; Chew and Leung, 1991; Zagon et al ., 1996; Nissen et al ., 1999), there is a shortage of information on local proenkephalin gene expression and its relationship to skin pathology and the environmental regulation of proenkephalin (PENK) expression.…”