Development of a Scientific Method for Classification of Facial Skin Types

Abstract

There is great variation in the nature and quality of facial skin in women. In the cosmetics industry, these variations in skin type have been classified subjectively as either oily, normal, or dry. Several physiological parameters of the skin were measured in an attempt to develop a scientific method for classifying skin types. Eighty women (age 20 to 59) participated in this one year study. Each was administered a skin type self-estimation questionnaire six times and answered puestions about the nature of their own skin. Parameters such as skin surface lipid quantity, transepideramal water loss (TWL), skin surface morphology, conversion rate of glutamic acid to pyrrolidone carboxylic acid (PCA%) were measured at the same time the self-estimation questionnaires ware given.
It was found that skin type is classified subjectively based on the independent sensations of “dryness” and “oiliness”. The former corresponded to TWL, skin surface morphology, and PCA% and the latter to skin surface lipid. The conventional skin classification procedure depends mainly on the level of skin surface lipids. This paper confirmed the existence of other parameters related to dryness.
Previous studies by the authors revealed that surface morphology reflected the biochemical events of keratinization, such as free amino acid metabolism including the glutamic acid to pyrrolidone carboxylic acid conversion rate, and also had a close relationship with TWL showing water barrier function and skin surface conductance indicating the water content of the stratum corneum. Thus, these parameters were found to be a valuable index for the water holding capacity of the skin.
A scientific method of skin classification based on the two factors of water holding capacity and skin surface lipid was developed. In addition to the three generally recognized skin types, an oily skin type characterized by dryness and roughness was identified. This paper presents a simple and reliable method for classifying skin types which has been approved from both dermatological and cosmetological aspects.