5HT, Serotonin; AAD, Aromatic amino acid decarboxylase; AANAT/NAT, serotonin-N-acetyltransferase(s); Anti-Inflammation; Antioxidation; CAT, catalase; COX-2, Cyclooxygenase-2; CYP450, cytochrome P450; Casp-1/3, caspase 1/3; DNCB, 2,4-dinitrochlorobenzene; GPx, Glutathione peroxidase; GSH, Glutathione; HIOMT, 4-hydroxyindole-O-methyl transferase; HO-1, heme oxygenase-1; HSP 70, Heat Shock Protein 70; IKK-α, IkB kinase-α; IL-1ß, interleukin-1 ß; IL-6, interleukin- 6; IkB, NF-κ-B inhibitor; Immunoregulation; MT, Melatonin; MT1/2, Melatonin receptor; Melatonin; NF-κB, Nuclear factor kappa-B; NQO1, NAD(P), quinone oxidoreductase 1; NQO2, NRH, Quinone oxidoreductase 2; Nrf2, Nuclear erythroid 2-related factor; Oncostatic mechanism; PEPT1/2, oligopeptide transporter 1/2; RNS, Reactive nitrogen species; ROS, Reactive oxygen species; RZR-α, Retinoid Z receptor α; SOD, superoxide dismutase; Skin barrier; TPH, tryptophan5-hydroxylase enzymes, including dominant TPH1 and TPH2; Trp, Tryptophan; iNOS, Inducible nitric oxide synthase; γ-GCS, c-glutamylcysteine synthetase