Conversely, factors providing negative regu- lation of melanogenesis include melatonin, interleukin (IL)-1, IL-6, tumor necrosis factor (TNF)-a and trans- forming growth factor (TGF)-b, interferon gamma (INF-g), glucocorticoids, triiodothyronine, and dopa- minergic and cholinergic agonists.21 It...