Abstract
We had found that skin dullness is caused by old corneocytes remaining on the skin surface due to the decrease of kallikrein (KLK)-5 activity of an exfoliating enzyme in skin. Furthermore, the increase of KLK-5 activity by our cosmetics formulation indicated a decrease of corneocyte area and skin dullness. In this study, we focused on KLK-7 which is similar to KLK-5 and decided to use plant extracts to determine whether skin dullness could be reduced via increased KLK-7 activity. In the primary screening, rosemary extract significantly increased KLK-7 gene expression and keratinocyte growth using RT-qPCR and WST-8 assay. Next, skin lotion containing rosemary extract was applied on half the face twice a day for 4 weeks as a clinical test. As a result, it was confirmed that the human stratum corneum KLK-7 activity increased in the group using skin lotion containing rosemary extract compared to the placebo. Furthermore, the stratum corneum area significantly decreased, and the skin dullness and stiff feeling by the subjects decreased, especially in female subjects using rosemary skin lotion. Water content and TEWL were not significantly different between the groups. The present study results suggest that rosemary extract may improve skin dullness and stiff feeling via a decrease of surface aggregation and corneocyte area in the stratum corneum by the increased KLK-7 activity. Because rosemary extract also indicated the growth of epidermal keratinocytes, it was considered that rosemary extract is useful for skin dullness and stiffness related to epidermal turnover that decrease with age.
