The skin is a complex immunological organ in which reactive oxygen species (ROS)-related pathways and host–microbe interactions synergically maintain immune homeostasis. Dysregulation of several oxidative mechanisms, including lipid peroxidation, mitochondrial dysfunction, ferroptosis, and impaired antioxidant defenses, alongside gut microbiome imbalance, is increasingly recognized as a key modulator of the immune response involved in disease onset and progression. However, their role in immune-mediated dermatoses remains incompletely defined. This narrative review aims to provide a comprehensive overview of the contribution of these altered pathways to the pathogenesis and prognosis of the major immune-mediated skin diseases. Across all conditions examined, elevated oxidative biomarkers, such as malondialdehyde (MDA), advanced glycation end-products (AGEs), advanced oxidation protein products (AOPPs), 8-hydroxydeoxyguanosine (8-OHdG), and reduced antioxidant capacity are consistently reported. Ferroptosis, driven by iron-dependent lipid peroxidation and dysfunction of Glutathione peroxidase 4 (GPX4), emerges as a relevant cell death pathway, particularly in psoriasis and atopic dermatitis (AD). In parallel, dysbiosis of the gut and skin microbiomes, characterized by depletion of short-chain fatty acid (SCFA)-producing taxa such as Faecalibacterium prausnitzii, Bifidobacterium, and Akkermansia muciniphila, has been reported across multiple diseases. Particular attention is given to shared molecular axes, such as the disruption of epithelial barrier integrity, activation of innate and adaptive immune responses, and the role of microbial-derived metabolites in modulating redox signaling, unraveling a bidirectional crosstalk. Emerging therapeutic strategies targeting these bidirectional crosstalks show biological plausibility and promising preliminary results. Integrating redox and microbial profiling into clinical practice may improve patient stratification and foster the development of more personalized therapeutic approaches beyond conventional immunological treatments.

Malondialdehyde (MDA) is one of the main end-products of lipid peroxidation (LPO) and represents a widely investigated marker of oxidative stress (OS) and oxidative tissue damage. Beyond its role as a measurable byproduct of polyunsaturated fatty acid peroxidation, MDA can interact with proteins and nucleic acids, generating adducts that may contribute to mutagenic, genotoxic, and cytotoxic events involved in carcinogenesis and tumor progression. This narrative review summarizes current evidence on the role of MDA in cancers, including breast, lung, head and neck, colorectal, cervical, and cutaneous tumors. Across these cancer types, increased circulating or tissue MDA levels have frequently been associated with enhanced LPO, impaired antioxidant defenses, tumor burden, advanced disease stage, aggressive histopathological features, treatment-related oxidative injury, and, in selected studies, poorer clinical outcomes. MDA-derived DNA adducts may further reflect oxidative DNA damage and provide mechanistic insight into the relationship between chronic redox imbalance, inflammation, and malignant transformation. However, MDA remains a non-specific biomarker influenced by age, smoking, diet, metabolic disorders, systemic inflammation, comorbidities, treatment exposure, and analytical methodology. Current evidence therefore supports MDA as a biologically relevant indicator of oxidative damage rather than a validated stand-alone diagnostic, prognostic, or therapeutic biomarker. Larger prospective studies using standardized and specific analytical methods are needed to clarify its clinical utility and to integrate MDA within broader redox biomarker panels.