Skin and Skin Care
Barrier function in cosmetics: Imokawa has reviewed mechanisms of the skin barrier and its association with cosmetics. Barrier function in the stratum corneum plays an important role in protecting the skin from penetration of environmental substances or infection by epidemic bacteria. However, because the phenotype of barrier disruption on the skin is not easily detectable, it remains obscure as to what skin issues can be attributed to a barrier defect.
In this review, an in vivo methodology for evaluating barrier function is described to reveal factors that induce barrier disruption as well as the effects of barrier replenishing substances such as synthetic ceramides. The methods include TEWL, riboflavin technique, nicotinic acid technique and photoacoustic spectrometry (PAS). Recently, several lipids other than free ceramide, a known barrier modulator, have been implicated to serve as barrier modulators and particularly are associated with UVB-induced barrier disruption. These include covalently bound ceramide and glucosylceramide, which are added or reduced based on the down-regulated activity of transglutaminase, or beta-glucocerebrosidase, respectively.