:
Skin being the largest external organ, offers an enticing procedure for transdermal drug delivery, so the drug needs to rise above the outermost layer of the skin, i.e., stratum corneum. Small molecular drug entities obeying the Lipinski rule, i.e., drugs having a molecular weight less than 500Da, high lipophilicity, and optimum polarity, are favored enough to be used on the skin as therapeutics. Skin's barrier action properties prevent the transport of macromolecules at pre-determined therapeutic rates. Notable advancement in macromolecules' transdermal delivery occurred in recent years. Scientists have opted for liposomes, the use of electroporation or, low-frequency ultrasound techniques. Some of these have shown better delivery of macromolecules at clinically beneficial rates. These physical technologies involve complex mechanisms, which may irreversibly incur skin damage. Majorly, two types of lipid-based formulations, including Solid Lipid Nanoparticles (SLNs) and Nanostructured Lipid Carriers (NLCs) are widely investigated as a transdermal delivery system. In this review, the concepts, mechanisms, and applications of Nanostructured Lipid Carriers that are considered feasible for transporting macromolecules via transdermal delivery system are thoroughly reviewed and presented along with their clinical perspective.