Morphological Characterization and Origin of Vernix Caseosa

In full-term newborns the epidermis is thicker and trans-epidermal water loss is lower than in adults, so the skin plays an important protective role [1]. In the first two days after birth, the epidermal stratum corneum is still adapting to extrauterine life and appears to be involved in the absorption of skincare products and topical medications [1,2]. Vernix caseosa is a physiological white barrier found on the skin of newborns that gradually covers the skin in a cephalocaudal manner during the final trimester of pregnancy [3]. Maternal and placental hormones control vernix caseosa formation and coverage [4]. Vernix caseosa is uniquely human and consists of waxes, sterol esters, squalene, cholesterol, triglycerides, and free sterols, as well as cellular elements [5]. To our knowledge, the cellular elements present in vernix caseosa have not been fully elucidated. Visscher et al. [4] suggested that the cells in vernix caseosa may originate from the hair follicles, which has a recognised local hypothalamic–pituitary–adrenal axis. Therefore, this study aimed to morphologically characterize the vernix caseosa, with a primary focus on its formation and the role of the hair infundibulum in this process. Vernix caseosa was gently scraped from the skin of 9 newborn infants and appropriately processed for morphological and ultrastructural analyses. Morphological evaluations revealed the presence of highly hydrated corneocytes embedded in lipids that were larger than those from the intact stratum corneum, suggesting they may be swollen with imbibed amniotic fluid. Transmission electron microscopy revealed flattened structures indicative of differentiated corneocytes, devoid of nuclei and intercellular lipids. Furthermore, the ultrastructural analyses indicated that vernix caseosa originates from the hair infundibulum. Although vernix caseosa is usually removed from the skin surface at birth, but it is not a “waste product” of human development. The present study supports the World Health Organization's recommendations to avoid wiping vernix off newborn infants’ skin at birth and to delay the first bath for at least six hours [4].