IL23A and psoriasis: SCFAs, generated through microbial fermentation of dietary fiber, modulate psoriasis severity via three key pathways (Figure 2): 1) suppression of regulatory T cell (Treg) differentiation, leading to overactivation of the IL-23/Th17 axis (126); 2) disruption of intestinal barrier integrity, enabling translocation of lipids, polysaccharides, and other metabolites that trigger systemic inflammation (127); and 3) modulation of the gut-brain axis, influencing neurotransmitter production and indirectly regulating cutaneous immune responses (128).