Seeing through the stratum corneum

The stratum corneum (SC) provides a vital barrier membrane between the external environment and the vulnerable internal tissues of the skin. It impedes the flow of water, the penetration of xenobiotics, and invasion of pathogenic micro-organisms. It also has protective capacity against ultraviolet radiation and thermal injury. As routine histopathology provides a misleading picture of a disorganized and shadowy SC, we would recommend the skin surface biopsy technique. This painless technique is easy and reliable in obtaining information from the SC. It demonstrates the geometric patterns of the surface, the openings of the eccrine ducts and hair follicles. The skin surface biopsy technique is also ideal for the investigation of the in situ microbiology of skin. Staining with periodic acid Schiff reagent makes it possible to see ringworm fungi, pityriasis versicolor, candida species, or erythrasma micro-organisms. Scanning electron microscopy can be employed when the higher magnification is needed. Histochemical applications include silver staining for melanin particle, potassium ferricyanide staining for blood pigments and lipid staining with Sudan red, for sebum. The rate of movement of topically applied drugs into the skin can be measured using the skin surface biopsy technique. The concentration of radiolabelled drugs can be counted and compared. Comedogenicity and DNA analysis are other applications of this non-invasive technique.