Introduction -- Biogenic Amines in the Skin -- Melatoninergic System in the Skin -- Cutaneous Cholinergic System -- Corticotropin Signaling System in the Skin -- Steroidogenesis in the Skin -- Equivalent of Hypothalamo-Pituitary-Adrenal Axis in the Skin -- Cutaneous Secosteroidal System -- Equivalent of Hypothalamic-Pituitary-Thyroid Axis -- Cutaneous Opioid System -- Cutaneous Endocannabinoid System -- Perspectives.