Relationships between visual and tactile features and biophysical parameters in human facial skin

Skin properties, such as colour, hydration and texture, can be studied on a qualitative basis by a clinical assessment or on a quantitative basis using techniques that measure biophysical properties of the skin. The aim of this study was to explore the links between facial skin features and a range of skin biophysical parameters using multivariate methods.

A study was conducted on 256 female volunteers from Ile-de-France with apparent healthy skin, aged between 20 and 50, under controlled environmental conditions (mean+/-standard deviation: room temperature 22.9+/-0.3 degrees C; relative humidity 48.5+/-2.3%). The study included a medical questionnaire and a clinical examination of the skin performed by a dermatologist, and a biophysical evaluation of the skin properties. Seventy visual and tactile skin features were assessed on the forehead and the cheek using ordinal variables illustrated by photographic scales. Twenty-eight biophysical measurements were taken in the same areas using the following equipment: Chromameter, Evaporimeter, Corneometer, Skicon, Sebumeter, Sebutape, skin thermometer, skin pH-meter and Silflo. In order to group the variables illustrating a same unimodal phenomenon, a typology of the skin features and a typology of the biophysical parameters were carried out using a clustering method. Then, the relationships between each group of clinical features and each group of biophysical parameters were studied using a series of partial least squares (PLS) regressions.

From eight groups of clinical features and three groups of biophysical parameters that were identified, 12 significant PLS regression models were built. Our findings suggest that differences in chromametric measurements express not only differences in skin colour but also differences in skin surface properties, such as skin vascularity status, thickness, and existence of wrinkles, and also demonstrate that the level of sebum excretion can affect other aspects of the skin surface.

Some skin features assessed clinically do not appear to be linked to any biophysical parameter. This finding confirms that certain phenomena evaluated on the basis of visual or tactile skin features are not assessed on the basis of the biophysical properties of the skin measured by our bioengineering techniques. Indeed, visual skin features mainly appreciate the skin surface aspect, contrary to some biophysical surrogate markers known to provide information on underlying epidermal structures. Therefore, both clinical and biophysical assessments must be associated to supply a relevant and accurate approach for skin aspect characterisation.