Thomas G. Polefka

Vitamin E Delivery to Human Skin by a Rinse-Off Product: Penetration of α-Tocopherol versus Wash-Out Effects of Skin Surface Lipids

α-Tocopherol, the major biologically active form of vitamin E, represents a frequently added lipophilic compound of skin care products. Despite its emerging use in rinse-off formulations, little is known on its efficacy with respect to its deposition or its antioxidant potential in human skin. The objective of this study was to investigate whether the single use of an α-tocopherol-enriched rinse-off product provides effective deposition of α-tocopherol on human stratum corneum. To test this, forearm skin of 13 volunteers was washed either with an α-tocopherol-enriched rinse-off product (test product, TP) or with an α-tocopherol-free vehicle control (control product, CP) (contralateral arm) using a standardized wash protocol. Thereafter, skin surface lipids were extracted with pure ethanol after the wash procedure as well as after 24 h. Additionally, one group of volunteers was subjected to irradiation of their forearms with low-dose UVA (8 J/cm2) prior to lipid extraction. Skin lipid extracts were analyzed by high performance liquid chromatography using electrochemical detection for vitamin E and UV detection for squalene (SQ) and squalene monohydroperoxide. The results of this in vivo study demonstrated that (1) while CP treatment lowers, TP treatment strongly increases α-tocopherol levels of skin barrier lipids; (2) increased vitamin E deposition levels were maintained for a period of at least 24 h, and (3) TP treatment significantly inhibited photooxidation of SQ. In conclusion, the use of α-tocopherol-enriched rinse-off products may help to maintain the integrity of the skin barrier by providing protection against photooxidative stress at the level of skin surface lipids.

The use of near-infrared spectroscopy in skin care applications

Background: Near‐infrared (NIR) spectroscopy was used to document the skin water content as a function of product usage and changes in the % relative humidity (%RH) in vitro and in vivo. The objective of the investigation was to determine if the NIR could provide comparable skin water content information as that obtained using gravimetric, conductivity, or visual assessment methods without having to invoke complex chemometric calculations.

Use of the dynamic vapor sorption meter to measure skin hydration properties, in vitro

Background: Maintaining an adequate skin moisture balance is important for retaining soft, pliable, healthy‐looking skin. This report describes the use of the dynamic vapor sorption (DVS) meter to quantify water content of skin in vitro under a variety of conditions. It is the only instrument that couples an ultra‐sensitive Cahn microbalance (resolution=0.1 μg) with an environmental system where both humidity and temperature are controlled. This feature is important since the skins water content is influenced by changes in the relative humidity.

The effects of prolonged use of surfactants on the skin of normal and photo-exposed hairless mice.

Laboratory tests to assess the irritant potential of materials, such as skin cleansers, which are normally used over a long period by humans, fail to mimic actual use. Most washing tests last a few days or at most a few weeks. Skin sites and techniques are often not standardized. The more standardized patch test involves occlusion and results in exaggerated reactions, since even water and blank patches produce visible and pathophysiologic changes. All of these tests rely on visual assessment despite strong evidence that similarly appearing skin can be very different histologically. The primary objective of this study was to use a well‐defined animal model to evaluate the cumulative effects of repeated skin exposure to low levels of surfactants of varying skin irritation potential. A secondary aim was to examine whether or not surfactant‐induced skin changes were exacerbated by suberythemal UV radiation. Test materials were applied topically, 2× daily to the dorsal areas of normal and low‐dose solar simulator exposed mice for 15 weeks. Our results show that, with conditions mimicking typical normal use, these surfactants and skin cleansers produce little or very mild histological changes in the skin. UV irradiation alone produced the greatest change in all histological parameters examined, with no synergistic or additive effects with the topical treatments.