## 7 Vitamin D in Cosmetics and Cosmetics  
Vitamin D has become an important part of dermatology because of its many advantages concerning skin health [209]. Its usefulness in different topical formulations, its underlying mechanisms of action, and its therapeutic efficacy in treating skin disorders have been brought to light by current scientific breakthroughs. Vitamin D is already used in skincare products in a variety of ways, each designed to meet unique dermatological requirements [81,124,210]. This hormone can, for instance, be found in creams, which are made to provide specific troubled skin areas with high concentrations of bioactive substances. When treating illnesses like psoriasis and AD, where localized treatment is vital, cosmetic formulations involving vitamin D have reportedly exhibited great results [121]. Because of their thick texture, creams can be applied deeply into the layers of the afflicted skin. In contrast to creams, lotions are designed with a lower viscosity and are appropriate for daily use. Lotions are therefore perfect for efficiently covering bigger body areas. Because of their thinner texture, vitamin D may be applied consistently, offering broad coverage. Moreover, sprays offer a practical way to get vitamin D into difficult-to-reach areas, providing a non-greasy substitute for creams and lotions, which makes them useful for people looking for a simple and fast application technique [121]. Ointments work well on excessively dry or irritated skin because of their thick, occlusive texture [211]. Such mixtures are dedicated to improving the absorption of vitamin D by creating a barrier, which prolongs the feeling of comfort and hydration. Because of their propensity to stay on the skin for a long time period, vitamin D has plenty of time to enter the body and initiate its function. Lighter options are provided by serums that are frequently mixed with different active components, which in turn, due to their composition, are less residual and enable tailored vitamin D administration [27]. Because of their quick absorption, serums are very helpful for targeted therapy regions. Vitamin D can also be found in infused oils mixed with ones, to increase their moisturizing capabilities, enhance their particularly helpful profile for people with dry skin types, and offer several therapeutic effects that improve the overall skin health. Numerous anti-aging and photoprotective effects towards human skin health, of vitamin D\({}_{3}\) and its active metabolites, derive from their utilization in cosmetic formulations [27]. These positive outcomes are accomplished by immunomodulation, which also regulates keratinocyte proliferation and differentiation so as to provide the epidermal barrier the ability to preserve skin homeostasis. Furthermore,vitamin D products trigger antioxidative reactions, prevent DNA damage, and promote DNA repair to reduce the risk of cancer's onset and premature skin aging. The activities of lumisterol metabolites are indeed comparable [27]. It is important to mention that the most frequently utilized type of vitamin D in skin-care is vitamin D\({}_{3}\). Because of its higher efficacy and stability, vitamin D\({}_{3}\) is preferred in skincare products over vitamin D\({}_{2}\). When it comes to increasing and/or preserving vitamin D levels in the body, vitamin D\({}_{3}\) is notably superior to vitamin D\({}_{2}\), while being more stable, ensuring that the medicine sustains its potency over time. Furthermore, because of its stability and efficacy, vitamin D\({}_{3}\) is the recommended ingredient in a variety of skincare formulations, such as oils, serums, ointments, lotions, and creams, as it keeps its effectiveness in a variety of formulations and blends in well with other active components [121; 212]. In addition, calcipotriol and 1\(\alpha\),25(OH)\({}_{2}\)D\({}_{3}\), two forms of vitamin D\({}_{3}\), are widely used to treat skin diseases including psoriasis.