Barrier Products for Topical Delivery-Insight into Efficacy Testing and Barrier-Boosting Compounds

The barrier effect refers to the ability of a topical product to protect the tissue against environmental factors, restore epidermal barrier function, or alleviate complications upon chemoradiation therapy. The market of barrier products for topical delivery is experiencing increased growth, and novel barrier-boosting compounds are being developed. However, only scarce reports and limited evidence justify their barrier efficacy. This may be due to the lack of a standardized, robust method for testing the protective effect of topicals. The paper reviews the recent advances in clinical and experimental techniques on the barrier efficacy of topical products, emphasizing those with the highest standardization potential. The principles and applications of each approach are specified, and the factors affecting the research outcome are highlighted. For predictive results, it is advised to mix at least two methods that differ in the mode of barrier efficacy testing. Combining quantitative TEWL and qualitative permeability testing not only balances out the limitations of each technique but also helps build high-quality evidence on the barrier efficacy. This review also summarizes the novel barrier-boosting ingredients and recent topical formulation strategies for enhancing product barrier efficacy and restoring the epithelial barrier function.