Participants and environmental condition
redness
We recruited and selected Korean women between the ages of 20 and 59 years with normal skin type. A normal skin type was judged based on a sebumeter's measured value of 30−60.Number of participants (To achieve exposure to a dry indoor environment in winter, the study was conducted in January and February, when humidity was low, according to the Korea Meteorological Administration website (Average daily temperature (T) and relative humidity (RH) during the study period.We evaluated the skin temperature, hydration, sebum, TEWL, elasticity, pores, texture, wrinkles, and redness on the participants’ faces and forearms before exposure (baseline) and 1 and 6 h after exposure. The participants waited for 6 h in an area maintained at a temperature of 25 ± 1°C and a humidity of less than 20% that was achieved by using a heater until the study was concluded.