IL6 and major depressive disorder: Regarding the mutual etiopathogenetic association between psoriasis and its psychological and mental comorbidities [53,54] (above all depression, anxiety, and suicidal ideation and behavior), the main overlapping biological (or more fittingly labeled psychodermatological) mechanism has been identified in systemic inflammation and subsequent pro-inflammatory habitus in the central nervous system (with leading involvement of IL-6) configuring the already-discussed “cytokine theory of depression” [54].