Molecular Role of Carbohydrates in Acne and Seborrheic Dermatitis.

Acne vulgaris and seborrheic dermatitis are common inflammatory disorders of sebaceous skin shaped by interactions among sebaceous activity, resident microorganisms, immune signaling, and host metabolism. This narrative review examines how high-glycemic dietary exposure may influence these disorders through insulin and insulin-like growth factor-1 (IGF-1) signaling, mammalian target of rapamycin complex 1 (mTORC1), sebaceous lipogenesis, and disease-specific microbial and inflammatory pathways. In acne, observational studies, mechanistic data, and small randomized trials support a biologically plausible model in which high glycemic index (GI) or glycemic load (GL) promotes hyperinsulinemia, IGF-1 signaling, PI3K/Akt/FoxO1/mTORC1 activation, altered sebaceous lipid production, follicular keratinization, and inflammation; however, clinical dietary trials remain inconsistent. Emerging observations with glucagon-like peptide-1 receptor agonists further suggest that systemic metabolic signaling may modify inflammatory follicular disease, although these data remain preliminary. In seborrheic dermatitis, Malassezia-host interactions, sebaceous lipids, barrier dysfunction, and inflammatory signaling are well established, but direct evidence linking dietary glycemic exposure to lesional IGF-1/mTORC1 activity or disease flares is lacking. The available evidence therefore supports dietary and metabolic factors as potential disease modifiers rather than uniform causes. Dietary counseling may be considered as an adjunct in selected patients with acne, whereas disease-specific carbohydrate restriction cannot currently be recommended for seborrheic dermatitis. Controlled mechanistic and interventional studies are needed to clarify causality and identify metabolically susceptible subgroups.