Improving the accuracy of skin elasticity measurement by using Q-parameters in Cutometer.

The skin elasticity parameters (Ue, Uv, Uf, Ur, Ua, and R0 through R9) in the Cutometer are widely used for in vivo measurement of skin elasticity. Their accuracy, however, is impaired by the inadequacy of the definition of a key parameter, the time point of 0.1 s, which separates the elastic and viscoelastic responses of human skin. This study shows why an inflection point (t(IP)) should be calculated from each individual response curve to define skin elasticity, and how the Q-parameters are defined in the Cutometer. By analyzing the strain versus time curves of some pure elastic standards and of a population of 746 human volunteers, a method of determining the t(IP) from each mode 1 response curve was established. The results showed a wide distribution of this parameter ranging from 0.11 to 0.19 s, demonstrating that the current single-valued empirical parameter of 0.1 s was not adequate to represent this property of skin. A set of area-based skin viscoelastic parameters were also defined. The biological elasticity thus obtained correlated well with the study volunteers' chronological age which was statistically significant. We conclude that the Q-parameters are more accurate than the U and R parameters and should be used to improve measurement accuracy of human skin elasticity.