Nano-Engineered Cosmetic Delivery Systems and Cutaneous Response: Linking Formulation Architecture with Skin Barrier Modulation and Dermatological Safety

Over the past two decades, nanotechnology has significantly transformed the cosmetic and cosmeceutical industries by addressing key limitations of conventional topical formulations, including poor skin penetration, instability of active ingredients, rapid degradation, and inconsistent delivery. Nano-engineered delivery systems, typically ranging from 1–100 nm, exhibit unique physicochemical properties that enhance stability, targeting, and controlled release of cosmetic actives. Common nanocarriers include liposomes, niosomes, solid lipid nanoparticles, nanostructured lipid carriers, polymeric nanoparticles, nanoemulsions, and dendrimers. These systems are designed to overcome the primary barrier of the skin, the stratum corneum, by enhancing intercellular permeation, exploiting follicular pathways, modifying skin hydration and lipid organisation, and acting as reservoirs for sustained release. The architecture of nano-formulations, such as particle size, surface charge, composition, rigidity, and functionalization, critically determines their interaction with the skin and subsequent biological responses. This paper critically evaluates the dermatological safety and biological fate of nanomaterials following topical application. Key concerns include penetration beyond the stratum corneum, systemic absorption, cytotoxicity, genotoxicity, oxidative stress, allergic sensitisation, and long-term accumulation risks. Evidence from in vitro, ex vivo, and in vivo studies is examined, alongside advanced testing models such as reconstructed human epidermis and three-dimensional skin equivalents. Regulatory perspectives from major authorities, including the European Union, U.S. FDA, and OECD frameworks, are discussed to highlight safety assessment requirements for commercialisation and scientific publication. Finally, emerging trends such as stimuli-responsive nanocarriers, bio-inspired systems, green nanotechnology, and artificial intelligence–assisted formulation design are explored as future directions in nano-cosmetics.