One-Year Clinical Trial of Olive Leaf Extract

In Japan, the environment changes depending on the season. In particular, the amount of UV rays increases in summer and the humidity decreases in winter. UV rays and dryness cause oxidative stress inside the skin, leading to various skin troubles. Therefore, it is important to suppress oxidative stress on the skin regardless of the season. We focused on leaves of olive (Olea europaea L.), which have excellent antioxidant properties but are discarded when pruning the branches to grow the fruit. Olive leaf extract promoted glutathione synthesis in normal human epidermal keratinocytes (NHEK). Next, we conducted a long-term clinical trial for one year. The lotion containing 2% olive leaf extract increased the brightness of the skin (L* value) in summer and decreased transepidermal water loss (TEWL), which is an index of skin barrier function, in winter. In addition, olive leaf extract promoted mRNA expression of kallikrein (KLK) 5 and KLK7, which are enzymes involved in stratum corneum desquamation, in NHEK. Olive leaf extract also promoted mRNA expression of serine protease inhibitor Kazal-type 5 (SPINK5), a gene encoding a KLK inhibitor. From the above results, we considered that olive leaf extract is a cosmetic material that can improve skin condition regardless of the season by its antioxidant effect and stratum corneum condition-improving effect.