Oxidative and Nitrosative Stress in Atopic Dermatitis and Depression: Similarities in Biomarkers and Pathophysiological Mechanisms

Background: Atopic dermatitis is a chronic inflammatory skin disease characterized by epidermal barrier dysfunction and immune dysregulation, whereas major depressive disorder is a common psychiatric condition with a substantial impact on quality of life; increasing attention has been given to oxidative and nitrosative stress as a potential biological link between these disorders. Methods: This narrative review synthesizes current evidence on molecular biomarkers of oxidative and nitrosative stress in AD and MDD and examines shared mechanisms within the skin–brain axis. Results: Across both conditions, studies consistently report increased markers of lipid peroxidation (e.g., malondialdehyde, 4-hydroxynonenal), oxidative DNA damage (8-hydroxy-2′-deoxyguanosine), and nitrosative stress, alongside impaired antioxidant defenses, particularly involving glutathione; these alterations are closely associated with chronic inflammation, cytokine signaling, mitochondrial dysfunction, and dysregulation of neuroimmune and hypothalamic–pituitary–adrenal axis pathways. Conclusions: Although the available evidence is heterogeneous and largely based on cross-sectional studies, limiting causal inference, the findings support a biologically plausible link between AD and depression mediated by shared redox pathways and highlight the need for further longitudinal and mechanistic research.