Natural and biotechnological antioxidants are increasingly interpreted through redox homeostasis rather than through simple free-radical scavenging. This narrative review examines ergothioneine, ovothiols, mycosporine-like amino acids, food-derived antioxidant peptides, and postbiotic antioxidant systems as examples of mechanism-dependent antioxidant strategies. Antioxidants biological value depends on transport, tissue localization, photoprotection, fermentation-derived production, digestive stability, gut-host interaction, and sustainable manufacturing. Ergothioneine illustrates the importance of dedicated uptake and tissue retention; ovothiols and mycosporine-like amino acids show how marine and stress-adapted organisms generate specialized redox and photoprotective metabolites; antioxidant peptides and postbiotics demonstrate the growing role of food biotechnology and microbiome-related products. The review also discusses why DPPH, ABTS, FRAP, and ORAC values should be treated as preliminary screening results rather than proof of in vivo efficacy. Overall, natural antioxidant development is strongest when chemical activity, mechanism-specific biomarkers, and reproducible manufacturing are considered together.