Validation of the elastic angle for quantitative and visible evaluation of skin elasticity in vivo

BACKGROUND: Reduction in skin elasticity due to aging causes skin sagging and wrinkles. Although there are various objective and reliable techniques for measuring skin elasticity, it is difficult to obtain a visual representation of skin elasticity with them. Therefore, we developed a novel device, the Swing anglemeter, and analyzed its effectiveness for measuring skin elasticity of the cheek. MATERIALS AND METHODS: Forty‐five healthy Korean women (age, 23‐60 years) participated. The Swing anglemeter works by dropping a rubber ball on a subject's cheek, which draws a curve as it collides with the cheek. After recording the movement of the ball using the slow‐motion function on a mobile phone, we defined the maximum angle at which the ball bounces off the skin as the elastic angle, using frame‐by‐frame video analysis. Changes in the elastic angle were assessed according to age, and correlation with the Ballistometer(®) results (Dia‐stron Ltd., Andover, UK) was analyzed for validation. RESULTS: Elastic angles differed significantly (P < .001) according to age. A negative correlation was found between the elastic angle and age (r = −.799, P < .001). Compared with the Ballistometer(®) measurements, the elastic angle was negatively correlated with alpha (r = −.570, P < .001); it was positively correlated with the mean coefficient of restitution and area (r = .602, P < .001 and r = .535, P < .001, respectively). CONCLUSION: The elastic angle is a useful parameter for reflecting skin elasticity, both quantitatively and visually. Our method can help subjects understand their skin elasticity status. Therefore, we expect the device will be utilized in various fields within the cosmetic industry.