BACKGROUND/AIMS: Two types of skin reflectance instruments are available nowadays for the determination of skin color: a tristumulus colorimeter (Chromameter from Minolta) using the CIE L*a*b* color system and the narrow-band simple reflectance meters (DermaSpectrometer from Cortex and Mexameter from Courage-Khazaka) using the erythema/melanin indices. The purpose of this study was to compare the capabilities of the three instruments (sensitivity, repeatability and correlation) in vitro and in vivo. METHODS: Comparative color measurements were carried out first in vitro on standardized color charts and subsequently in vivo on different skin areas in human volunteers. Skin color changes induced by various physico-chemical treatments were also quantitatively evaluated with the three instruments. RESULTS: The in vitro and in vivo repeatabilty as well as the sensitivity of the three instruments are rather good. Erythema and skin blanching could be readily quantified by the increase of the a* parameter and of the erythema indices of the simple reflectance meters. Natural UV tanning and artificial chemical tanning could be measured by the decrease of L* and increase of b* and of the melanin indices. CONCLUSION: The Chromameter and the two narrow-band reflectance instruments were able to characterize skin color and to quantify small skin color changes. Moderate to high significant linear correlations could be established between the CIE L*a*b* color parameters and the erythema/melanin indices.

Both instruments allow a certain calibration and both give good estimates of the SC hydration.

The preservative properties of thyme essential oil (3%) with a known composition were evaluated in two types of final formulations, suitable for use as pharmaceutical or cosmetic vehicles, by means of a standard challenge test proposed by the latest European Pharmacopoeia. The required preservation efficacy criteria were satisfied against the bacterial strains, against the yeast in one of the formulations, but not against the mould strain involved in this study. Interactions between the essential oil compounds and other factors present in the final formulation might have influenced the activity of this essential oil, leading to an incomplete satisfaction of the criteria.

The measurement of transepidermal water loss (TEWL) is an important noninvasive method in order to assess the barrier function of the stratum corneum. As a consequence, TEWL has been found to be a very useful technique for studying skin irritation induced by various physical and chemical effects. Exposure of the skin to chemicals (detergents) and physical conditions (occlusion and stripping) generally results in an increase of TEWL. Until recently the only commercially available TEWL instrument was the Evaporimeter^® developed by ServoMed (Sweden). The instrument is based on the open chamber system with two humidity and temperature sensors which measure the water evaporation gradient at the surface of the skin. Recently a new commercially available instrument based on the same physical principle of measurement was developed by Courage and Khazaka (Tewameter^®, FRG). Our aim in this study has been to compare the measuring capacities of both instruments. The accuracy, sensitivity, variability and reproducibility of both instruments were compared in vivo under identical conditions on normal skin and skin damaged by external conditions. The influence of external and environmental factors such as air and probe temperature, relative humidity, air turbulence and pressure of application was evaluated for both instruments. Finally, the two instruments were compared in practice when following the increase in TEWL of the skin after stripping, occlusion and exposure to irritant household detergents. A very good correlation (r = +0.97) was found between the results of the two instruments over a wide range of TEWL values.

Chronic exposure of the skin to sunlight causes damage to the underlying connective tissue with a loss of elasticity and firmness. Silicon (Si) was suggested to have an important function in the formation and maintenance of connective tissue. Choline-stabilized orthosilicic acid ("ch-OSA") is a bioavailable form of silicon which was found to increase the hydroxyproline concentration in the dermis of animals. The effect of ch-OSA on skin, nails and hair was investigated in a randomized, double blind, placebo-controlled study. Fifty women with photodamaged facial skin were administered orally during 20 weeks, 10 mg Si/day in the form of ch-OSA pellets (n=25) or a placebo (n=25). Noninvasive methods were used to evaluate skin microrelief (forearm), hydration (forearm) and mechanical anisotropy (forehead). Volunteers evaluated on a virtual analog scale (VAS, "none=0, severe=3") brittleness of hair and nails. The serum Si concentration was significantly higher after a 20-week supplementation in subjects with ch-OSA compared to the placebo group. Skin roughness parameters increased in the placebo group (Rt:+8%; Rm: +11%; Rz: +6%) but decreased in the ch-OSA group (Rt: -16%; Rm: -19%; Rz: -8%). The change in roughness from baseline was significantly different between ch-OSA and placebo groups for Rt and Rm. The difference in longitudinal and lateral shear propagation time increased after 20 weeks in the placebo group but decreased in the ch-OSA group suggesting improvement in isotropy of the skin. VAS scores for nail and hair brittleness were significantly lower after 20 weeks in the ch-OSA group compared to baseline scores. Oral intake of ch-OSA during the 20 weeks results in a significant positive effect on skin surface and skin mechanical properties, and on brittleness of hair and nails.