Effects of petrolatum on stratum corneum structure and function.

Ointments (e.g., petrolatum) are thought to be occlusive, thereby blocking transcutaneous water loss and trapping water under the skin's surface. If this premise is correct, then petrolatum should delay barrier recovery after barrier perturbation, as shown previously in occluded murine skin. We reexamined the assumption that Vaseline Petroleum Jelly (VPJ) is occlusive, ascertaining both its site and mechanism of action. Barrier recovery was measured in VPJ-treated versus untreated sites after acetone-induced barrier disruption in human volunteers. Moreover, VPJ was localized within the stratum corneum (SC) with tracers and ruthenium tetroxide staining, which allowed visualization of the depth of VPJ penetration and its relation to intercellular membrane structures. VPJ accelerated, rather than impeded, barrier recovery. Moreover, VPJ was present within the interstices at all levels of the SC, where it replaced intercellular bilayers. VPJ neither forms nor acts like an epicutaneous impermeable membrane; instead, it permeates throughout the SC interstices, allowing normal barrier recovery despite its occlusive properties.