## 4 Natural Antioxidants and Their Role in Cosmetics
### Selected Plant Species with Antioxidant Activity
#### 4.11.2 Camellia sinensis ([PERSON]  
_C. sinensis ([PERSON] (Theaceae) is grown mainly in Japan and China but also in Taiwan and to a lesser extent in India. Green tea is one of the oldest beverages in the world. The chemical composition of this infusion is very similar to the chemical composition of freshly picked leaves, except for the enzymatic changes that occur rapidly after the leaves are picked. Green tea leaves contain a lot of vitamins, amino acids, fiber, and minerals. Green tea also contains many active substances, such as polyphenols, flavonoids (catechins), tannins, and purine alkaloids [206]. Numerous studies have confirmed that polyphenols contained in green tea are strong antioxidants [207]. The effect of tea catechching on free radicals is multifaceted, encompassing several mechanisms: the direct scavenging of reactive oxygen species (ROS) and reactive nitrogen species (RNS); the chelation of trace elements that contribute to the generation of free radicals; the stimulation of endogenous antioxidant enzyme production, such as superoxide dismutase (SOD) and glutathione; the inhibition of enzymes involved in ROS production, including glutathione S-transferase, microsomal monooxygenase, mitochondrial succinate dehydrogenase, and NADH oxidase; and the protection and regeneration of antioxidant compounds like vitamins C and E [208]. The antioxidant properties of tea represent the primary and one of the oldest applications of _C. sinensis_ extracts in the cosmetics industry. Given that oxidative stress is a key factor in skin aging, natural antioxidants are considered crucial in mitigating this process. Polyphenols, abundant in tea, help protect and restore vitamin C levels, an essential coenzyme in collagen synthesis. Collagen is a vital protein that contributes to skin elasticity and strength, working in conjunction with elastin and keratin to maintain the skin's structural integrity. Various tea types, including black, white, and green, have been utilized in skincare formulations. However, green tea is most frequently incorporated due to its higher concentration of polyphenols. In addition to polyphenols, other components of the tea plant, such as vitamins, lipids, and pigments, provide additional skin benefits, including moisturizing and protective effects. Tea leaf extract absorbs ultraviolet radiation, offering protection against its harmful effects, and is commonly used in photoprotective cosmetics for daily skincare. The photoprotective properties of green tea can be enhanced when combined with other herbal extracts. One such plant, _Ginkgo biloba_, has been shown to significantly boost the photoprotective efficacy of green tea extract when included in cosmetic formulations [209]. Tea extracts exhibit a broad range of biological activities, making them valuable not only in pharmaceutical applications but also in the cosmetic industry. Notable among these activities are their antioxidant, photoprotective, anticellularite, slimming, and skin and hair conditioning properties, as well as their ability to enhance microcirculation [209]. Moreover, the reported functions of _C. sinensis_ ingredients include acting as an antifungal agent, antimicrobial agent, cosmetic astringent, fragrance ingredient, light stabilizer, oral care agent, skin protectant, and skin conditioning agent--emollient, humectant, and miscellaneous [32]. Camellia Sinensis-derived ingredients are used in various cosmetic and personal care products at different concentrations. Camellia Sinensis leaf extract is reported to be used in amounts of up to 2% in leave-on products, 1% in rinse-off products, and 0.14% in ingestible oral hygiene products. Camellia Sinensis leaf powder is used at concentrations of up to 7% in body and hand products and 0.01% in rinse-off products. Camellia Sinensis leaf water is primarily found in mascara formulations, with usage levels reaching up to 30%. Camellia Sinensis seed extract is used at concentrations of up to 0.1% in leave-on products and 0.0013% in rinse-off products.