## 3 Vitamin A, Its Vitaminoids and Carotenoids' General Profile and Health Benefits
### Anti-Aging and Photo-Protective Properties of Vitamin A, Retinoids, and Carotenoids
#### 5.1.2 Photo-Protective Effect
Such antioxidant capacity stems from their unique molecular structure, featuring a long chain of conjugated double bonds (polyene chain) that can readily donate electrons to stabilize free radicals; hence, the number of conjugated double bonds determines their antioxidant capacity [19; 136; 137]. Lycopene with 11 conjugated double bonds owns the highest antioxidant efficiency, followed by \(\alpha\)-carotene, \(\beta\)-cryptoxanthin, \(\beta\)-carotene, zeaxanthin, and lutein [19]. Vitamin A and carotenoids act as very effective quenchers of singlet oxygen, both in vivo and in vitro, by reacting with free radicals, breaking them down into active degradation products [16]. Notably, dietary supplementation with carotenoids has been proved to increase the antioxidant status of the skin, resulting in a lower concentration of free radicals generated in the skin after sunlight exposure to a simulator [19; 138]. Moreover, carotenoids may also enhance the activity of the skin's endogenous antioxidant enzymes and have the ability to combat ROS and RNS [134; 139]. Topical application of several carotenoids, primarily as an ingredient in cosmetic preparations, increases carotenoid levels in the _stratum corneum_, the outermost layer of the skin, preventing skin damage caused by free radicals from UV rays and other factors [127; 139]. At this point it must be noted that the less unsaturated, colorless carotenoids, namely phytoene and phytofluene, in contrast to the more saturated lycopene, have not displayed as exceptional an antiradical ability, even though they have been proved as great skin-whitening agents [8]. As a result, \(\beta\)-carotene, for instance, has been confirmed as a great antioxidant candidate in sunscreens, with a great role against sunflowered lipid peroxidation [61], while a recent crossover study demonstrated that lutein capsules stabilized by 10% of the antioxidant carnostic acid may protect from photodamage by reducing UV\({}_{\text{R}}\)-modulated gene expression like heme-oxygenase 1 (HO-1), intercellular adhesion molecule 1 (ICAM-1), and matrix metallopeptidase 1 (MMP1) genes [8; 140]. Interestingly, oral supplementation with a red paprika product led to notable MED and hydration enhancement and a reduction in skin tanning in skin previously exposed to UV on the back [141]. At the same time, the anti-inflammatory properties of carotenoids stem from their ability to modulate cellular signaling pathways involved in inflammation. Carotenoids can interact with the NF-\(\kappa\)B pathway, inhibiting its activation and subsequent production of inflammatory mediators. They can also reduce the expression of inflammatory markers such as interleukin 24 (IL-24) in keratinocytes [19; 29; 113; 136]. Oxidative stress, induced by factors like UV radiation and pollution, is a major driver of inflammation in the skin. By valuably scavenging free radicals and quenching singlet oxygen, carotenoids aid in reducing oxidative stress, thereby mitigating the inflammatory cascade [142]. Additionally, some carotenoids, like \(\beta\)-carotene, can be metabolized into retinoids, which are known for their potent anti-inflammatory effects in the skin [8; 143]. Retinoids can regulate keratinocyte differentiation, reduce sebum production, and modulate immune responses, contributing to the overall anti-inflammatory benefits of carotenoids in cosmetics. Caroenoid structure allows them to neutralize ROS and absorb UV radiation, offering protection from environmental damage such as pollution and sun exposure, benefits that translate into an enhanced skin tone and a strengthened skin barrier [8; 143].