ABSTRACT
In the dermato-cosmetic world, evaluation of the skin looks at first glance rather easy since the skin is very accessible for clinical evaluation (1,2). Visual examination reveals color, dryness, oiliness, roughness, ageing, etc. Tactile evaluation by feeling reveals also dryness and oiliness, plus roughness, firmness, laxity, ageing, etc. Even olfactory examination can be carried out, which reveals information on perspiration, microbial colonization, and antiperspiration. As an example, human vision is a very sensitive sensory and neurophysiological process. Experience shows that we have a high sensitivity and discriminative power at low intensities of luminosity. Our color discriminative power is so high that 0.5% to 1% differences in color can be easily detected. Our sensitivity at higher intensity of luminosity is much less present. On the other side, this neurophysiological process is very limited, subjective, mostly qualitative, highly observer dependent, and there is no precise memorization of color in function of time. The sensitivity in the visible region is not constant in function of wavelength with a maximum of sensitivity in the green color (490-550 nm). On the contrary, the use of tristumulus reflectance colorimeters using the CIELAB L*a*b* color system, which is internationally accepted, delivers a quantitative, accurate, and reproducible analysis of the skin color and can be calibrated with standard color charts (3).
