## 4 Natural Antioxidants and Their Role in Cosmetics
### Carotenoids
#### 4.2.5 Coenzyme Q10  
Coenzyme Q10 (Figure 3) is a derivative of quinone and is structurally similar to vitamins A and E. It is a factor necessary for cell life. It has oxidoreductase properties and it is an essential element of the respiratory chain--it participates in the transfer of protons and electrons. Coenzyme Q10 can occur in two forms: oxidized (ubiquone) and reduced (ubiquinol). It should also be emphasized that only the reduced form of CoQ10--ubiquinol--has antioxidant properties. It is a fat-soluble antioxidant, the reduced form of which can constantly regenerate from the oxidized form thanks to the presence of various enzymes [74].  
Coenzyme Q10 is a lipophilic antioxidant that plays a crucial role in neutralizing free radicals generated during the citric acid cycle and initiating the synthesis of endogenous antioxidants. Additionally, it regenerates other antioxidants, enhancing cellular defense mechanisms. As a widely recognized ingredient in cosmetics, coenzyme Q10 is primarily utilized in formulations targeting mature skin, particularly for its anti-aging properties. While coenzyme Q10 in topical applications does not penetrate the viable layers of the epidermis and dermis, it remains beneficial for various skin types. Its antioxidant activity helps slow the aging process in mature skin; reduces inflammation associated with conditions such as acne vulgaris, adult acne, and rosacea; and diminishes melanocyte activity to mitigate hyperpigmentation. However, the mitochondrial and ATP synthesis-enhancing effects of CoQ10 are not achieved through topical cosmetics. Such outcomes require systemic supplementation or targeted cosmetic procedures like needle mesotherapy. This method allows for the direct delivery of coenzyme Q10 into the deeper dermal layers, where it contributes to the synthesis of collagen, elastin, and glycosaminoglycan fibers. When integrated into a holistic cosmetic regimen, this approach effectively reduces wrinkles, enhances skin firmness, and improves hydration through the combined action of coenzyme Q10 and supplementary agents like hyaluronic acid [75; 76]. Coenzyme Q10 (CoQ10) plays a significant role in cosmetics and dermatology, particularly in providing protection against UVA radiation. When applied to the skin, CoQ10 penetrates epidermal cells and effectively shields keratinocytes from oxidative stress. Cosmetics containing CoQ10 help smooth the skin and enhance its tone. The inclusion of CoQ10 in cosmetic formulations is well-tolerated and does not cause adverse effects such as skin burning or irritation, making it suitable for use on sensitive skin [77].  
The maximum concentration for leave-on use in this ingredient group is 0.05% for ubiquinone in body and hand products [32].  
Currently, coenzyme Q10 used in cosmetics is primarily obtained through microbial fermentation (_Paracoccus denitrificans_, _Rhodobacter spheroides_). Synthetic production is less common but still present in conventional products. Q10 can be chemically synthesizedfrom organic precursors, such as tyrosine-based or isoprenoid-based synthesis. Extraction from natural sources has limited application due to low efficiency and high costs. Biotechnological production methods of Q10 are gaining popularity as they ensure purity, stability, and sustainability, aligning with trends in anti-aging and protective cosme [78; 79].