Since the 1970s, the canonical brick and mortar model proposed by Peter Elias has served as the foundational framework for understanding the barrier function of the human stratum corneum, depicting corneocytes embedded in a continuous lipid matrix of ceramides, cholesterol, and free fatty acids. While this conceptualization remains influential, the discovery of a greatly expanded diversity of ceramides—now encompassing over a dozen major classes and hundreds of molecular species—has reshaped our understanding of how barrier lipids are organized, processed, and regulated. Competing and complementary models, including the long periodicity phase (LPP), short periodicity phase (SPP), the crystalline and liquid ordered co existence models, and orthorhombic vs. hexagonal lateral packing, will be discussed.

Professor Johan Engblom, PhD (engineering) in biophysical technology. Engblom entered the field of skin research at Lund University in 1989 from a lipid crystallography perspective with X-ray diffraction as a major technique, working closely with among others Prof. Bo Forslind, dermatologist at Karolinska Institute. After more than a decade in pharma industry focused on development of products for topical drug delivery, Engblom returned to academia in 2007 as Director of Biofilms Research Centre for Biointerfaces (BRCB, https://mau.se/brcb) and later Head of Dept. Biomedical Science (https://mau.se/bmv) at Malmö University. Engblom’s current research focus is to link physical and pharmaceutical science over biology to the clinical reality. The ultimate objective is to adopt a holistic perspective and utilize the power of multidisciplinary research to generate new knowledge that facilitates development of new and competitive products targeting health, disorders and healing of biological barriers.