*2.3. Particulate Systems*

Particulate systems are delivery systems that include nano/microspheres and nano/ microcapsules (Figure 3B) [25]. Whereas nano/microspheres are dispersions of active ingredients in polymeric matrices, nano/microcapsules are reservoirs where distinct domains of core and wall material are present. These formulations create a compatible environment for susceptible molecules and protect them from light, oxygen, pH, heat, enzymatic degradation and other external factors that can affect their stability [41]. Microencapsulation technologies are widely used in cosmetic products to increase stability, protect against degradation, promote safe administration and allow controlled and targeted release [42]. Particle size varies from around one micron to a few millimeters, providing a large surface area available to develop active ingredients. Nanoparticles involve particulate systems in the nano range, providing a larger surface area that is available for adsorption and desorption sites, chemical reactions, light scattering, etc. [42]. Studies on which particulate systems have been used are summarized in Table 3.

**Table 3.** Summary of AST particulate delivery systems, describing the preparation technique, system type, characterization and stability data, and assays (in vitro/in vivo) that were performed for each system.

