Gut-skin axis: Emerging insights for gastroenterologists-a narrative review

Table 2 Shared cytokine pathways in gut and skin disorders

Cytokine	Source	Role in gut disease	Role in skin disease
IL-17	Th17 cells	Promotes mucosal inflammation in Crohn’s disease; may have protective roles in UC	Drives psoriasis, AD
IL-23	Dendritic cells, macrophages	Supports Th17 expansion in IBD	Involved in psoriatic inflammation
TNF-α	Macrophages, monocytes	Central to both Crohn’s and UC pathogenesis	Targeted in psoriasis, hidradenitis suppurativa
IL-4	Th2 cells	Mucosal immunity shift in some IBD variants	Hallmark of atopic dermatitis
IL-6	Multiple immune cells	Acute phase reactant in IBD	Links gut-brain-skin inflammation
IFN-γ	Th1 cells	Epithelial barrier disruption	Found in psoriatic and alopecia lesions
IL-22	Th17 cells, innate lymphoid cells	Promotes epithelial regeneration, but may drive pathology in IBD (e.g., UC)	Promotes keratinocyte proliferation in psoriasis

IL: Interleukin; UC: Ulcerative colitis; IBD: Inflammatory bowel disease; AD: Atopic dermatitis; IFN-γ: Interferon-gamma.