## 9 Future Directions and Research
Beyond traditional encapsulation, emerging encapsulation techniques like solid lipid nanoparticles (SLNs), nanostructured lipid carriers (NLCs), and stimuli-responsive carriers could offer superior protection, and sustained release, and target both oral and topical vitamin D delivery, while improving stability, enhancing bioavailability, minimizing potent degradation, and responding to environmental changes (e.g., pH, temperature, UV exposure) [65,268]. Optimizing vitamin D's use in cosmetics also requires a deeper understanding of its molecular and cellular actions. Scientists should focus on clarifying the exact pathways through which vitamin D impacts skin health, encompassing its effects on cell differentiation, proliferation, and barrier function. Examining the role of coregulatory proteins and _VDR_ in these processes will provide critical insights into how vitamin D works and how its effects can be maximized in cosmetic formulations. Also, exploring how vitamin D interacts with other signaling pathways, like those connected to oxidative stress and inflammation, may reveal novel therapeutic targets and improve product development. Safety is of paramount importance when formulating cosmetic products, and long-term research is required to evaluate vitamin's D efficacy. Future studies could explore as well how vitamin D affects melanogenesis and pigmentation pathways. Such product development could lead in successfully targeting pigmentation disorders, like melasama, or developments aiming to even out skin tone (skin tone regulation) [25,269,270]. The skin microbiome plays a vital role in maintaining skin health. Therefore, studies could focus on investigating how vitamin D influences the skin microbiome and whether combining vitamin D with prebiotics, probiotics, or postbiotics in cosmetic, cosmeceutical, and nutticosmetic formulations can lead to enhanced skin barrier function and resilience against environmental stressors [271, 272, 273]. While vitamin D is essential for overall health, excessive use of high-concentration products over extended periods may have adverse effects. Research should hence focus on long-term safety evaluations, such as potential skin reactions, systemic absorption, and combinations with other topical or systemic treatments. Rigorous clinical trials and post-market surveillance are necessary to guarantee that consumers are not exposed to risks from vitamin D-based cosmetics and that any potential side effects are promptly identified and addressed [269]. Innovative delivery systems offer promising avenues for enhancing the effectiveness of vitamin D in skincare. Research into new delivery methods, such as microneedle systems (e.g., patches), microemulsions, smart skin patches, bioengineered vitamin D precursors, nanoencapsulation carriers, photonic delivery, quantum dot systems, or hydrogel matrices, could enable more efficient and controlled release of vitamin D into the skin. These advanced systems may enhance the penetration and targeting of vitamin D to specific skin layers where it can exert its beneficial effects [72,274, 275, 276, 277, 278]. Exploring combination the therapies that integrate vitamin D with other active ingredients like antioxidants or anti-inflammatory agents could amplify the overall efficacy of cosmetic products. Although the number of studies describing the emerging technologies appear large at first glance and various strategies have been covered, they are all at an early research stage [64]. As personalized skincare continues to grow in popularity, future studies should investigate vitamin D's role in customized skincare uses. Individual responses to vitamin D are influenced by genetic and environmental factors; a better understanding of these variables might result in more individualized and efficient treatments.