Natural Ingredients of Transdermal Drug Delivery Systems as Permeation Enhancers of Active Substances through the Stratum Corneum

In recent years, significant progress has been made intransdermaldrug delivery systems, but there is still a search for enhancers thatcan improve the absorption of active substances through the stratum corneum. Although permeation enhancers have beendescribed in the scientific literature, the use of naturally occurringsubstances in this role is still of particular interest, because theycan offer a high level of safety of use, with a low risk of skin irritation,and high efficiency. In addition, these ingredients are biodegradable,easily available, and widely accepted by consumers due to the growingtrust in natural compounds. This article provides information on therole of naturally derived compounds in transdermal drug delivery systemsthat help them penetrate the skin. The work focuses on the componentsfound in the stratum corneum such as sterols, ceramides,oleic acid, and urea. Penetration enhancers found in nature, mainlyin plants, such as terpenes, polysaccharides, and fatty acids havealso been described. The mechanism of action of permeation enhancersin the stratum corneum is discussed, and informationon the methods of assessing their penetration efficiency is provided.Our review mainly covers original papers from 2017 to 2022, supplementedwith review papers, and then older publications used to supplementor verify the data. The use of natural penetration enhancers has beenshown to increase the transport of active ingredients through the stratum corneum and can compete with synthetic counterparts.