Vitamin C<br /> Vitamin C (ascorbate, ascorbic acid) is low-molecular-weight and water soluble vitamin which is essential for the body. L‑ascorbic acid (LAA) is biologically the active form of vitamin C which is useful in medical practice. Most plants are able to synthesize vitamin C from glucose, humans and vertebrates lack the enzyme L‑glucono‑gamma lactone oxidase needed for synthesis of vitamin C.<br /> The two main layers of skin from outer is the epidermis and dermis, the epidermis represents the barrier of the skin, that is predominantly consist keratinocytes cells. The cells with lipid-rich field that formation barrier known as the stratum corneum. Dermis supply the skin with nutrition and it is rich with nerve endings and blood vessels. Also it provides strength and elasticity, dermis is relatively cellular (fibroblasts are the major cells present in the dermis that are responsible for the synthesis of many of the extracellular matrix components) and is primarily consist of complex extracellular matrix proteins which is rich in collagen fibers. The level of vitamin C in skin is 30 mg/kg, vitamin C found in the epidermis is 2–5-fold more than that found in the dermal layer. In photodamaged or aged skin the level of vitamin C are low. The excessive exposure UV irradiation or pollutants (oxidant stress) is associated with lower level of vitamin C in the epidermal layer.<br /> The mechanism by which vitamin C is up taken from the plasma then transported across the skin layers depends on sodium-dependent vitamin C transporters (SVCTs), the epidermis expresses two types of vitamin C transporters ( SVCT1 and SVCT2), while dermal cells (such as fibroblasts) expresses SVCT2 that can diffuse ascorbic acid and transports it from plasma to epidermis, then SVCT1 present in the epidermis which supply ascorbic acid to keratinocytes.<br />The Role of Vitamin C in Skin:<br />1- Antioxidant:<br /> Vitamin C is a potent antioxidant that can neutralize (electron donor) and remove oxidants (ROS and reactive nitrogen) which contributes to the protection of cells from the damaging effects of these oxidants such as during immune activation or UV radiation . Vitamin C is one of non-enzymatic antioxidant defense mechanisms that include (uric acid, vitamin E and glutathione), when ROS accumulated over the level of antioxidant defenses cause skin diseases, such as exposed the skin to UV radiation this will lead to generation of oxygen radical cascade which cause an alteration in the structure of lipids, nucleic acids and proteins that may cause skin tumors.<br />2- Melanogenesis inhibition: <br /> Melanin synthesis in the melanocytes that present in the basal layer of the epidermis then transported to keratinocytes, thus melanin is distributed through the epidermis. The tyrosinase enzyme oxidizes tyrosine and 2- hydroxyphenylalanine to melanin, vitamin C inhibits the action of tyrosinase enzyme by interacting with copper ions at the tyrosinase active site thereby decreasing the formation of melanin.<br /><br /><br />3- Collagen synthesis Promotion: <br /> In the skin, the formation of collagen is achieved by the fibroblasts in the dermis, vitamin C is essential for proliferation of the basement membrane and dermal collagen matrix, therefore it is essential for collagen biosynthesis, as it act as co‑factor for the enzymes prolysyl and lysyl hydroxylase which are responsible for stabilization and cross‑linking of the collagen molecules .In addition, vitamin C is an important agent to preserve dermal collagen by increases collagen mRNA production by fibroblast, thus it improves the dermal matrix. Moreover vitamin C has beneficial effect on wound healing and the impairment of wound healing is an early indicator of hypovitaminosis C. Therefore, severe vitamin C deficiency can cause fatal scurvy disease which is characterized by poor wound healing, weak collagenous structures, reduce in the thickness of the stratum corneum, subcutaneous bleeding (due to loss of the connective tissue morphology and fragility) and immunity impairment which are highly susceptible to fatal infections such as pneumonia.<br />4-Anti-inflammatory and immune- modulating effects: <br /> Vitamin C inhibits nuclear factor kappa beta (NF-kB), which is responsible for the activation of a number of pro‑inflammatory cytokines such as IL1, IL6, IL8 and (TNF‑α). <br /> Moreover, vitamin C increases T-cell maturation which result in an enhancement of immune function, therefore vitamin C has an immune-modulating effects.<br /> Thus, as vitamin C has a potential anti‑inflammatory activity it can be used in certain conditions such as acne vulgaris and rosacea, also can enhance wound healing and prevent post‑inflammatory hyperpigmentation, it can be used as an adjuvant agent for the treatment of acne scars by micro needle which improved skin smoothness, postinflammatory pigmentation and hardness. Moreover it is used in treatment of atopic dermatitis, psoriasis, the pathology of these conditions involves an activation of allergic or auto-immune inflammation with generation of cytokines and cellular dysfunction, and consequently breakdown of the skin barrier.<br /><br /> Naturally vitamin C founds in the vegetables and fresh fruits, synthetic preparations of vitamin C are available with different formulation such as tablets, effervescent tablets and liquid vials, the prophylactic dietary vitamin C which is needed to optimize cell and tissue levels is ( 100–200 mg/day) such amount can reduce the occurrence of infection, for healthy adults, it should be no more than (2000mg /day). Vitamin C concentrations in plasma can reach up to 1–15 mg/ml (10–160 mM) after ingestion of vitamin C enriched diet, and the excessive vitamin C excreted by kidneys. However, vitamin C is contraindicated in patients with deficiency in G-6PD, renal insufficiency.<br />