## 4 Natural Antioxidants and Their Role in Cosmetics
### Taxifolin
#### 4.3.2. Phenolic Acids  
Ferulic acid (4-hydroxy-3-methoxycinnamic acid) (Figure 4) is an organic chemical compound and a derivative of cinnamic acid, classified as a phenol. It contains a hydroxyl and carboxyl group in its structure [94]. Due to its antioxidant properties, ferulic acid protects the skin from the harmful effects of external factors. Due to the presence of side chains with double bonds and aromatic rings, it destabilizes free radicals, reduces oxidative stress and prevents the formation of thymidine dimers, which lead to cell DNA damage and biological changes in the skin. It absorbs a beam of solar radiation by creating a phenoxy radical. It has anti-inflammatory effects by reducing the concentration of inflammatory mediators, inhibiting the expression of iNOS protein and interferon. In addition, it has antibacterial, antiviral, anti-allergic and blood vessel-sealing effects [95]. It is used in anti-acne therapy, both in rosacea and acne vulgaris, and is also recommended for the treatment of skin discolorations [96]. In cosmetic products, ferulic acid is mainly used to improve skin elasticity and firmness, maintain uniform color, inhibit skin aging processes, reduce fine wrinkles, alleviate inflammation, and strengthen the skin barrier against oxidative stress [96]. Ferulic acid helps neutralize the free radicals generated by UVA radiation, providing protective effects to endothelial cells and keratinocytes, which are typically vulnerable to this type of damage. In human fibroblasts, ferulic acid administration before UVA exposure notably reduced the harmful effects of radiation. This includes preventing UV-induced alterations in the cell cycle and protecting DNA integrity. It regulates the expression of genes involved in DNA repair, supporting cellular recovery and enhancing the skin's resilience to UV-induced damage. UVB-induced reactive oxygen species (ROS) play a major role in the development of skin cancer by causing oxidative damage to skin cells, including DNA mutations that can lead to tumor formation. Ferulic acid, a potent antioxidant, has been shown to reduce the levels of these harmful ROS, making it a promising substance in cancer prevention. Ferulic acid has long been used in cosmetics as a stabilizer for well-known antioxidants like vitamin C and vitamin E. However, recent research highlights that ferulic acid is not just a supporting compound but also an active ingredient with its own powerful antioxidant properties. It actively contributes to the skin's defense systems, offering multiple benefits for skin health and appearance. By strengthening antioxidant defense, it plays a protective role for key skin components, including keratinocytes, fibroblasts, collagen, and elastin. This helps to maintain the structural integrity and overall health of the skin. Ferulic acid is commonly used in skin-lightening formulations due to its ability to inhibit the activity of tyrosinase, an enzyme crucial in the process of melanogenesis (the production of melanin). By reducing tyrosinase activity, ferulic acid helps to limit melanin production, which can reduce dark spots, hyperpigmentation, and overall skin discoloration. Ferulic acid is increasingly used in various dermatological procedures, such as microneedling, non-needle mesotherapy, chemical peels, and grooming treatments, due to its potent antioxidant, anti-inflammatory, and skin-repairing properties. It is particularly effective in addressing a variety of skin concerns [96; 97; 98; 99]. The production of ferulic acid for cosmetics predominantly relies on extraction from plant-based sources, particularly rice bran derivatives, due to their high content of ferulic acid esters. This process typically includes base-catalyzed hydrolysis of \(\gamma\)-oryzanol, a compound found in rice bran oil, to release ferulic acid. Biotechnological methods are emerging as promising alternatives, offering sustainable and efficient production routes.