Noncontact method for measuring skin hydration and sebum using optical reflected skin images

Conventionally, hydration and sebum content of the skin, especially which on the face, have been measured using commercial instruments that compute variation in resistance through probes. These probes must be attached to the skin tissue, which significantly increases the probability of pollution or infection during measurement. Therefore, in this paper, we propose a noncontact method that employs optical reflected skin images obtained by irradiating the skin with green and near-infrared light with wavelengths of 528 nm and 770 nm, respectively, to evaluate skin hydration and sebum content. The difference in the skin sebum content of the forehead between the evaluated value from the reflected image and the measured value using the contact method was less than 3%. In addition, we built a sebum distribution map, and the difference in sebum content determined from the skin images of two tested subjects was evident. The proposed method offers the advantages of a noncontact measurement process and large measurement area alongside two-dimensional distribution information. Moreover, the results can serve as a reference for determining skin quality, including sebum content and hydration retention, in the medical and beauty industries.