*3.6.3 Topical delivery*

Hydrophilic and lipophilic drugs poorly penetrate the skin due to the limitations of their solubility in both the lipid phase and aqueous solution. The topical delivery of drugs via nanoparticle formulations has several advantages over other conventional topical methods for the treatment of skin disorders while showing minimal side effects. Nanoparticles can incorporate both lipophilic and hydrophilic drugs. Additionally, drug degradation, salivary degradation, and hepatic first-pass metabolism in the stomach can be avoided, while benefiting from sustained drug delivery, long-term stability, enhanced permeability, and reduced toxicity [49, 50].
