## 4 Natural Antioxidants and Their Role in Cosmetics
### Taxifolin  
Taxifolin (Figure 4), also known as 3,5,7,3\({}^{\prime}\)A\({}^{\prime}\)-pentahydroxylavanone or dihydro-quercetin (TXF), is a flavonanol with potent antioxidant properties, widely distributed in nature in both aglycone and glycoside forms. It is commonly sourced from onions, olive oils, grapes, citrus fruits, milk thistle, maritime pine bark, and Douglas fir bark. The antioxidant and free-radical-scavenging activities of TXF have been extensively validated through various in vitro bioanalytical assays. Taxifolin consists of two aromatic rings, each containing phenolic groups (-OH) positioned at the meta- and para- sites relative to each other. These phenolic groups contribute significantly to its potent antioxidant activity. The strong antioxidant properties of taxifolin are primarily attributed to the conjugated structures and the resonance stability of both phenolic rings. The presence of a C2-C3 double bond is critical for the inhibitory activity of flavonoids; however, taxifolin lacks this bond, rendering it more susceptible to inactivation through the formation of strong hydrogen bonds with macromolecules [89].  
Additionally, the 3-hydroxy group (3-OH) in the C ring plays a key role in modulating the oxidative burst of neutrophils, highlighting its anti-inflammatory potential. In the B ring, the ortho arrangement of the catechol group is crucial for the modulatory effect of taxifolin against neutrophil oxidative burst. This structural configuration enhances its ability to influence cellular oxidative processes, contributing to its therapeutic efficacy in inflammatory conditions [89; 90].  
Scientific evidence highlights TXF's multifunctional bioactivity, including its roles as an anti-inflammatory, depigmenting, and antitumor agent. It has been shown to mitigate oxidative DNA damage and prevent UV-induced skin carcinogenesis. TXF exhibits low toxicity and effectively protects the skin from photoaging while inhibiting melanogenesis. Furthermore, it is among the most potent flavonoids in suppressing the interferon-\(\gamma\) (IFN\(\gamma\))-induced expression of intercellular adhesion molecule-1 (ICAM-1) protein and mRNA in human keratinocytes. Pre-treatment with TXF also significantly inhibits IFN\(\gamma\)-induced ICAM-1 expression in reconstructed human skin models, indicating its therapeutic potential for pathological skin conditions associated with heightened cellular adhesion and inflammation [91].  
In vivo studies on experimental animal models have demonstrated TXF's efficacy in alleviating chemically induced atopic dermatitis-like lesions and promoting recovery in chemically induced burn injuries. These findings underscore TXF's potential as a promising candidate for the management of oxidative stress-related and inflammatory skin disorders [91].  
Currently, extraction from _Larix sibirica_ and _Larix gmelinii_ remains the primary method of taxifolin production, but biotechnological methods (using engineered microorganisms, such as the yeast _Yarrovai lipolytica_) are emerging as sustainable alternatives. Stabilization techniques are also being explored to improve its effectiveness in cosmetic formulations. These advancements align with the growing demand for natural, high-performance skin-care ingredients [92]. Due to its limited solubility and stability, taxifolin is often modified into derivatives (e.g., taxifolin tetraocanoate) to enhance its performance in cosmetic formulations [93].