## 3 Vitamin A, Its Vitaminoids and Carotenoids' General Profile and Health Benefits
### Skin and Other Cancers' Treatment Potential of Vitamin A, Retinoids, and Carotenoids  
Skin cancer is another result of over-exposure to the sun's radiation. Photo-protection is once again the solution to avoid this undesirable and mostly irreversible condition, operated either topically or systematically. The main aim of this treatment solution is the achievement of UV light absorption by certain bioactive groups, like phenols, vitamins, and carotenoids. Such antioxidants may prevent UV\({}_{\text{R}}\) by penetrating the skin and causing the formation of ROS, which eventually leads to skin cancer and photo-carcinogenesis, along with other side effects. Both in vivo-animal model and in vitro studies have proved the protective impact of carotenoids against skin cancer. Astaxanthin also inhibited skin cancer and tyrosinase over-activity in a rat model, while a trial among Australian volunteers showed that a diet rich in lutein and zeaxanthin was associated with a decrease of SCC in people with a family background of skin cancer (Figure 11) [8; 130]. Figure 11: Activity of astaxanthin, lutein, and zeaxanthin carotenoids in skin cancer prevention. Briefly, similar studies conducted on other retinoids and carotenoids have implied their notable potential towards several cancer disorders. Meals enriched with \(\beta\)-carotene were effective against esophagus cancer, lutein and zeaxanthin minimized the risk of breast cancer, and lycopene had a lower risk of prostate cancer and heart failure, while retinoid precursors prevent cancer in sunburn reactions [18]. Carotenoid and retinol treatment in human breast, cervix, prostate, colorectal, oral cancer, and leukemia has been confirmed highly effective [16]. A lower incidence of epithelial lung cancer and respiratory diseases (acute lung injury) was also observed in patients receiving a high carotenoid intake that restrains ROS and induces apoptosis in tumor cells [3; 123; 124]. Vitamin A and Its Derivatives of Several Sources: Health-Promoting Skin Benefits for Nutricosmetic, Cosmeceutical, and Cosmetic Applications  
Retinoids and carotenoids have multiple benefits and have great clinical importance towards several diseases, disorders, and comorbidities. Lutein as a nutraceutical and nutricosmetic is able to mitigate the likelihood of ocular complications like cataract, retinitis pigmentosa, and age-related macular degeneration (AMD) [123; 148]. Regarding hyperhomocysteinemia, coronary artery dyslipidemia, diabetes mellitus (type II mainly), hyperhomocysteinemia, atherosclerosis, metabolic disorders, CVDs, steatohepatitis, and neurodegenerative diseases, carotenoids modulate pro-inflammatory mediators (e.g., cytokines), thereby lowering blood pressure and improving insulin sensitivity [124]. Several health-related bioactive compounds are traced in functional foods, including fruits, vegetables, animal-based, marine-associated, and many microorganism-related products, naturally rich in bioactive compounds like carotenoids (e.g., tomatoes, citrus fruits, eggs, fish). Nutricosmetics, cosmeceutical, and cosmetics are supplementary or topical formulations generated to deliver such bioactives directly via controlled dosage for health or aesthetic benefits. Carotenoids like \(\beta\)-carotene, \(\alpha\)-carotene, \(\beta\)-cryptoxanthin, astaxanthin, zeaxanthin, lutein, lycopene, fucoxanthin, phytoene, and phytofluene are highlighted as key players in skin health [109; 149; 150]. A vital role of carotenoids is their antioxidant capacity, due to combating oxidative stress by neutralizing ROS and helping cellular damage. Meanwhile, these constituents are also photo-protective against harmful UV radiation, hence reducing photo-dermatoses (against _Erythopoietic protoporphyria_ (EPP), _Porphyria cutane tarda_ (PCT), premature skin aging-cancer, and polymorphic light eruption (PMDE)) risk, as well as sun-induced erythema, photo-carcinogenesis, photo-aging, pigmentation, and melanogenesis disorders like melasma.