Issue link: https://www.ascpskindeepdigital.com/i/1544125
30 ASCP Skin Deep Spring 2026 The Science of Serums Understand delivery pathways and formulation to better assist clients by Stacy Best-Nervis GETTY IMAGES SKIN PHYSIOLOGY THE SKIN CARE INDUSTRY IS seeing substantial growth of innovative ideas, starting with forward- thinking ingredients and products. Serums fall into that category. Serums contain concentrated ingredients that stimulate activity for desired skin results, like hydration, brightening, exfoliation, and more. Knowledge of how serums are delivered into the skin is vital in determining what is best for your clients and their desired changes. It's often assumed that the more a product penetrates the skin, the better the results. Although this is not always the case, product penetration aff ects skin sensitivity and displays the skin's tolerance of the ingredients. It's important to understand the terminology used with delivery systems of serums into the skin. Penetration is the process of serums going through the layers of the skin by three primary pathways: • The transcellular route involves going through the keratinocytes. • The intercellular route involves passing between the intercellular lipid matrix surrounding the corneocytes. • The transappendageal route moves through the pores, hair follicles, and sebaceous glands. 1 By design, human skin acts as a barrier against substances that could be absorbed into the skin. The permeable molecular size for substances such as a serum to move through the stratum corneum is known to be below 500 Daltons (Da), also known as the 500 Dalton Rule.