We present our latest study on human hair water content and water holding capacity measurements by using capacitive contact imaging and condense-TEWL method. Previous studies showed that capacitive contact imaging based fingerprint sensors, originally designed for biometric applications, can be used for skin hydration imaging, skin surface analysis, 3D skin surface profiles, skin micro-relief as well as solvent penetration measurements. Through calibration, we can also measure the absolute dielectric constant, and from which we can calculate the absolute water content of the samples. In this study, we used capacitive contact imaging for hair water content measurements, and compared it with other measurement techniques. The results show that capacitive contact imaging can effectively differentiate different hairs from different people, normal hair from wet hair, and water content changes in hair. Healthy hair always contains certain amount of water, and they will contain different amount of water when exposed to different relatively humidity (RH) environments. We studied this water holding capacity by using the condenser-TEWL method through desorption process, in which small hair samples were placed inside the measurement chamber (22ΒΊC and 11.3% RH). These hair samples, pre-conditioned at different higher RH, will therefore lose water until they reach equilibrium with the chamber RH. The dynamics of the equilibration process can be studied by measuring time-series curves of associated water vapour flux. The total quantity of water lost can then be calculated from such time-integrated flux curves. We have also developed mathematical models for modelling this hair desorption process. By fitting the normalized hair desorption data with the mathematical models, we can get the water diffusion coefficient information, which can then be related to the water holding capability of the hair samples
