Biophysical changes after mechanical injury of the stratum corneum in normal skin

Scrubbing off the stratum corneum with a rough towel after soaking in warm water is a bathing custom unique to Korea. However, Korean dermatologists have advised against this practice due to the potential harm that it may cause, though there is little data to support this advice. This study aimed to evaluate the changes in biophysical characteristics after such mechanical injury of stratum corneum, as reflected by water-holding capacity, stratum corneum barrier function, and stratum corneum turnover time (SCTT). 10 Korean female volunteers (aged 19-34 years) were enrolled in this study to investigate the acute effects and 32 volunteers (aged 19-49 years) the chronic effects. After soaking in warm water (36 degrees C) for 5 min, the flexor surfaces of the forearms were scrubbed with a rough towel. The volunteers' forearms were divided into 4 compartments, and each compartment was scrubbed 0, 5, 10, and 15x, respectively. After a single injury of the stratum corneum, there was an initial decrease in water-holding capacity until 6 h. Thereafter, it increased until day (D) 3, when it began to descend to the normal range. The transepidermal water loss (TEWL) values also peaked at D2 and declined thereafter. However, there were no changes in either water-holding capacity or skin barrier function, and only the SCTT was significantly shortened, after chronic injury of the stratum corneum.