The viscoelasticity of the facial skin changes with age. Viscoelasticity has been related to the tactile softness of the skin as well as the morphological sagging of the face. 1 Hence, skin viscoelasticity is an important skin physical property for esthetic purposes.Skin viscoelasticity has been measured through various methods. Conventionally, viscoelasticity is measured starting from the skin surface using a typical device, such as Cutometer 2 or Venustron. 3 These measuring devices detect alteration in the skin surface by applying stimuli such as suction and vibration onto the skin surface. The viscoelasticity of the whole skin depth is estimated from the change of the surface. Meanwhile, the skin is made up of multiple layers such as stratum corneum, epidermis, dermis, and subcutaneous fat layers, with different physical properties. Therefore, the abovementioned devices only provide physical properties appearing on the skin surface

Background Oxygen is essential for life, and investigation of the skin's oxygen environment and identification of its effects on the skin may lead to the discovery of new antiaging targets. To understand individual skin differences and age‐related changes, we developed a noninvasive method using near infrared spectroscopy (NIRS) to measure the regional saturation of oxygen (rSO2) of human skin. Materials and methods To construct an NIRS sensor probe specialized for skin measurement, the distance between the sensor transmitter and receiver was optimized based on data for the thickness of the facial skin to the subcutaneous fat layer. To analyze the relationship between skin oxygen saturation and body oxygen saturation, rSO2 was measured by NIRS, oxygen saturation of peripheral artery (SpO2) was measured by pulse oximeter, and physical conditions were considered, such as body mass index (BMI) and muscle mass, in Japanese women (age 20s–60s). Results Both skin rSO2 and SpO2 varied among individuals and decreased with age. Only SpO2 showed a relationship with BMI and muscle mass, whereas rSO2 showed no relationship with these physical conditions. No relationship between rSO2 and SpO2 was observed. Conclusion Individual and age‐related differences in skin by rSO2 values were found by NIRS optimized for local skin; however, the factors affecting rSO2 differed from those affecting SpO2, and further study is needed.