Evaluation of Cosmetic Liquid Penetration Using Terahertz Time-of-Flight Method

It is important to evaluate the penetration depth and speed of cosmetics into the skin for the cosmetic industry. However, the conventional method for measuring those parameters has some drawbacks. In this study, a terahertz time-of-flight method with Si-based emitter was applied for evaluation. The penetration of the liquid into a pig skin was measured as a travelling time of the THz pulses irradiating on a pigskin, where the glycerin concentration in the liquid was varied.