In addition, exogenous nutrients, such as α-tocopherol, β-carotene, lycopene, and lutein, could contribute to forming the UV barrier via enzymatic and non-enzymatic mechanisms ( Thiele, 2001 Eichler et al., 2002 Larsson et al., 2006 Evans and Johnson, 2010). Urocanic acid, which is generated from histidine in skin, is a potent, endogenous UV absorbent ( Barresi et al., 2011). The influence of UV irradiation depends upon the structure of cellular components. These anti-oxidants maintain skin homeostasis i.e., protection of proteins/lipids from oxidation ( Tyrrell and Keyse, 1990 Thiele et al., 2001). A number of antioxidant chemicals, including vitamin C, are present in the skin ( Thiele et al., 2001). In addition to acidification, antimicrobial barrier function can be improved by the action of antimicrobial peptides, which are expressed in epidermal keratinocytes to kill invaded microbial pathogens ( Park et al., 2011 Park et al., 2013b). Since maintenance of skin pH below 5.5 is vital for suppressing virulent microbial pathogen growth, including Staphylococcus aureus, skin acidification is essential in enhancing the antimicrobial barrier ( Elias, 2007). Of the multiple factors that contribute to the maintenance/improvement of the permeability barrier, a well-known cutaneous lipid, ceramide, serves as a key constituent in epidermal membrane ( Uchida and Hamanaka, 2006). The permeability barrier prevents loss of excess water from nucleated layers of epidermis and penetration of harmful chemicals, allergens, and pathogens into the epidermis ( Elias and Friend, 1975). Skin deploys multiple barrier functions i.e., permeability-( Elias and Friend, 1975), antimicrobial- ( Elias, 2007), antioxidant- ( Thiele et al., 2001), and UV-barrier ( Thiele et al., 2001) ( Table 1), to protect our bodies from external perturbants.
In this review paper, the author will describe briefly various functions of the epidermal barrier with a focus on the role of selected micronutrients in maintaining skin integrity. A decrease in nutritional status can alter the structural and biological function of skin, resulting in skin abnormalities, including dry skin ( Boelsma et al., 2003 Cosgrove et al., 2007 Lakdawala et al., 2013). Notable examples of nutrients are calcium and vitamin C, which are responsible for the differentiation of keratinocytes, a major cell type in epidermis ( Bikle et al., 2001 Uchida et al., 2001). Proper nutritional intake complements endogenous factors in regulating skin barrier function ( Boelsma et al., 2003 Lakdawala et al., 2013). Nutritional status, dependent on both macro and micronutrients, is vital for skin health ( Boelsma et al., 2003 Lakdawala et al., 2013). The outermost layer of epidermis is the stratum corneum. The skin consists of two primary layers, epidermis and dermis. Intact skin of mouse was subjected to hematoxylin and eosin (H&E)-staining.
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