Abstract
The development of methods for objectively and accurately assessing skin condition is an important challenge in cosmetics research. There are currently several promising methods for displaying assessment results that combine quantitative and numerical data with images and other visual data, and that are intuitively easy to understand at a glance. Softness and elasticity of skin are of particular interest to consumers, and while it is possible to show numerical data, it has been difficult to show visual data for these. We therefore attempted to develop a method for objectively assessing skin softness and elasticity that shows both numerical and visual data, and proposed the sphere-drop test. The sphere-drop test involves dropping a sphere from directly above the skin so that it free-falls in a perpendicular line, impacts the skin, and rebounds back, and filming the process with a high-speed camera adjacent to the impact area. This test gives both numerical and visual data on sphere displacement over time. One of the sphere-drop test parameters, compression time (t1+t2), showed a highly significant positive correlation with sensory evaluations for skin softness. Another parameter, rebound height (h2), showed a highly significant positive correlation with sensory evaluations for skin elasticity. As these parameters can be visualized with images in addition to numerical expressions, this method may be a new objective assessment method for visualization of mechanical properties of skin with strong tactile elements.
