TABLE 1.
The stratum corneum and simultaneous multitasking: Individual epidermal barrier functions
| BARRIER FUNCTION | MAJOR COMPONENTS |
|---|---|
| PERMEABILITY BARRIER | Formation of stratum corneum lipids in specific ratio from precursor lipids |
| Production of lamellar bodies packaging precursor lipids and some antimicrobial peptides | |
| Formation of natural moisturizing factor from filaggrin (converted from profillagrin) | |
| Formation of cornified envelope and the corneocyte-lipid envelope | |
| Maintenance of water gradient, calcium gradient, acid mantle (acidic pH) | |
| Response of primary proinflammatory cytokines to impairment of permeability barrier | |
| ANTIMICROBIAL BARRIER | Maintenance of an acidic skin pH decreases skin colonization by pathogenic bacteria and yeasts |
| Antibacterial activity of stratum corneum lipids (e.g., free fatty acids, sphingosine, others) | |
| Genetically encoded primary antimicrobial peptides (defensins, cathelicidins, dermcidins) synthesized in SC, present in sebum and in sweat (dermicidin-derived) | |
| Multiple agents with antimicrobial activity as alternative function (some chemokines, some neuropeptides, others) | |
| ANTIOXIDANT BARRIER | Network of enzymatic and nonenzymatic antioxidant systems to counter oxidative stress |
| Antioxidants present in epidermis (stratum corneum, skin surface lipids) and dermis | |
| Hydrophilic nonenzymatic antioxidants include ascorbic acid (vitamin C) and uric acid | |
| Major lipid-soluble nonenzymatic antioxidant is alpha-tocopherol (vitamin E) | |
| Co-antioxidants (ascorbic acid, ubiquinol [coenzyme Q10]) allow tocopherol regeneration | |
| Gradients in stratum corneum for ascorbic acid and tocopherol (lowest near surface) | |
| Interceptive antioxidant enzymes (catalase, superoxide dismutases, glutathione peroxidases) | |
| Antioxidant repair enzymes (e.g., methionine sulfoxide reductase) | |
| High concentration of alpha-tocopherol in sebum accounts for high levels in facial sebaceous gland stratum corneum (sebum serves as a physiological delivery pathway) | |
| IMMUNE RESPONSE BARRIER | Dendritic cells involved in immune surveillance and antigen recognition (e.g., plasmacytoid dendritic cells, myeloid dendritic cells, Langerhans cells) |
| Toll-like receptors involved in recognition of microbial pathogens and other agonists | |
| Antimicrobial peptides and some of their enzymatic conversion products (e.g., LL-37) | |
| Innate and acquired immune response pathways and balance with T regulatory cell system | |
| PHOTOPROTECTION BARRIER | Epidermal melanin barrier (degree of protection related to Fitzpatrick skin ttype) |
| Stratum corneum protein barrier | |
| Antioxidants within stratum corneum (protection against photo-oxidative stress) | |
| Optical reflective properties of the stratum corneum (stratum corneum thickness more important than epidermal thickness for ptrotection against ultraviolet/solar radiation) |
Reprinted with permission from: Del Rosso JQ, Levin J. J Clin Aesthet Dermatol. 2011;4(9): 22-42. © 2011 Matrix Medical Communications.