Background: The influence of various environmental factors on skin properties is well known. However, there is a lack of research into the effect of quarantine masks on skin properties, even though the use of masks has significantly increased after the COVID‐19 outbreak. Therefore, this study aimed to investigate the influence of mask use on skin properties.Materials and Methods: Twenty subjects were enrolled in this study. The subjects used approved quarantine masks for 6 hours a day for 2 weeks. We measured eight skin biophysical parameters: temperature, redness, pore volume, texture, elasticity, trans‐epidermal water loss (TEWL), sebum content, and pH, and evaluated acne lesions before and after using quarantine masks. The evaluation was performed on the mask‐wearing area of the face.Results: Skin temperature, redness, and TEWL increased significantly after a 6‐hour mask use, while the sebum content increased marginally. Skin elasticity was reduced by the use of masks over 1 and 2 weeks, whereas the pore volume and the number of acne lesions increased after a 2‐week mask use. The skin changes caused by mask use showed sex‐based differences in the skin elasticity (after 6 hours), redness, and roughness (after 2 weeks).Conclusions: The use of quarantine masks causes a change in the skin temperature, redness, and TEWL in the short term and in skin elasticity, pores, and acne in the long term. This study revealed that prolonged mask use could have negative effects on the skin.

Background: The stratum corneum (SC), the outermost layer of the skin epidermis, acts as an effective bi‐directional barrier, preventing water loss (inside–outside barrier) and entry of foreign substances (outside–inside barrier). Although transepidermal water loss (TEWL) is a widely‐used measure of barrier function, it represents only inside‐outside protection. Therefore, we aimed to establish a non‐invasive method for quantitative evaluation of the outside–inside barrier function and visually present a skin barrier model. Materials and methods: Skin barrier damage was induced by applying a closed patch of 1% sodium dodecyl sulfate to the forearms of eight participants; they were instructed to apply a barrier cream on a designated damaged area twice daily for 5 days. The SC barrier was evaluated by measuring TEWL and fluorescein sodium salt penetration rate before, immediately after, and 5 days after damage. The penetration rate was assessed using tape‐stripping (TS) technique and fluorescence microscopy. Results: The rates of fluorescein sodium salt penetration into the lower layers of SC differed significantly based on the degree of skin barrier damage. The correlation between penetration rate and TEWL was weak after two rounds of TS and became stronger after subsequent rounds. Five days after skin barrier damage, the penetration rate of all layers differed significantly between areas with and without the barrier cream application. Conclusion: Our findings demonstrated that the penetration rate was dependent on skin barrier conditions. The penetration rate and corresponding fluorescence images are suitable quantitative indicators that can visually represent skin barrier conditions.