Towards Optimal pH of the Skin and Topical Formulations: From the Current State of the Art to Tailored Products

Acidic pH of the skin surface has been recognized as a regulating factor for the maintenance of the stratum corneum homeostasis and barrier permeability. The most important functions of acidic pH seem to be related to the keratinocyte differentiation process, the formation and function of epidermal lipids and the corneocyte lipid envelope, the maintenance of the skin microbiome and, consequently, skin disturbances and diseases. As acknowledged extrinsic factors that affect skin pH, topically applied products could contribute to skin health maintenance via skin pH value control. The obtained knowledge on skins’ pH could be used in the formulation of more effective topical products, which would add to the development of the so-called products ‘for skin health maintenance’. There is a high level of agreement that topical products should be acidified and possess pH in the range of 4 to 6. However, formulators, dermatologists and consumers would benefit from some more precise guidance concerning favorable products pH values and the selection of cosmetic ingredients which could be responsible for acidification, together with a more extensive understanding of the mechanisms underlaying the process of skin acidification by topical products.

Role of emollients in the prevention of skin diseases in young children

Epidermis plays an important role in protecting the body from negative environmental influences. The horny layer plays a special role in carrying out these functions. Skin defense mechanisms are multistage and include 5 protective barriers responsible for maintaining the integrity and performing the main functions of the skin. The first one is a microbial barrier – determined by commensal flora which prevents contamination of pathogenic microorganisms; the second one is a physical barrier preventing mechanical skin damage, penetration of allergens and microorganisms; the third one is a chemical barrier achieved by forming pH and components of natural moisturizing factor as well as epidermal lipids; the fourth one – immune barrier – Langerhans cells, tissue basophils, lymphocytes etc.;the fifth is the neurosensory barrier – numerous nerve endings transmitting signals of skin integrity damage and controlling metabolic processes and homeostasis maintenance. Epidermal barrier of newborns and infants is imperfect and differs in its structure and functional activity from that of adults. Children’s skin is prone to excessive dryness, irritation, allergic reactions and inflammation. For young children, it is very important to minimize the risk of these manifestations. Individual selection and use of emollients in the basic care of infants promotes the functional stability of five protective «frontiers» of the epidermal barrier: prevents skin damage when exposed to unfavorable environmental factors, reduces TEWL, supports the normal microbiome, has antipruritic and anti-inflammatory action. Modern emollients restore the hydrolipidic layer of the epidermis and prevent the development of dermatitis and skin infection in children. An important role when choosing an emollient is played by its texture, which can be represented by a lotion, cream, balm, ointment. Chemically, creams, lotions and balms are emulsions, i.e. they consist of two immiscible components – fat (oil) and water. In this case, one of the components is in the other in the form of tiny droplets. Most skin diseases faced by young children are related to the integrity of the epidermis, which is why daily care should be primarily focused on protecting the skin barrier

Nature or Nurture: Can Prey-Based Diets Influence Species-Specific Physiological Performance Traits of Epidermal Lipid Content and Cutaneous Water Loss?

Synopsis Epidermal lipids serve as the primary barrier to cutaneous water loss (CWL) and play a significant role in water conservation and homeostasis. Previous studies have shown the correlation between increased aridity of habitats and the amount of epidermal lipids among species. Generally, increased amounts of epidermal lipids lower skin permeability. Species-specific differences in CWL and prey preferences between two sympatric snake species, the Northern Cottonmouth (Agkistrodon piscivorus) and the Eastern Copperhead (Agkistrodon contortrix), motivated us to question if prey-base can result in these observed species-specific differences in CWL. We experimentally controlled the diets for a captive colony of Northern Cottonmouths (A. piscivorus) by feeding either fish (Notemigonus crysoleucas) or mice (Mus musculus) to investigate if diet can affect the quantity and quality of epidermal lipids and the rates of CWL. Snakes fed mice gained consistently more mass, but diet treatments did not affect growth rate. We found no significant differences in quantitative lipid content or rates of CWL between diet treatments. An analysis for qualitative lipid content using infrared spectrophotometry also showed no diet effect, thus suggesting that lipid content and CWL are strong species-specific physiological performance traits not influenced by recent dietary history. While there is some evidence that epidermal permeability may be variable under certain environmental conditions (e.g., humidity), our findings show that diet has no effect and that a shift in prey preference may not influence or enhance physiological performance for decreasing CWL.

Catalytic activities of mammalian epoxide hydrolases with cis and trans fatty acid epoxides relevant to skin barrier function

Lipoxygenase (LOX)-catalyzed oxidation of the essential fatty acid, linoleate, represents a vital step in construction of the mammalian epidermal permeability barrier. Analysis of epidermal lipids indicates that linoleate is converted to a trihydroxy derivative by hydrolysis of an epoxy-hydroxy precursor. We evaluated different epoxide hydrolase (EH) enzymes in the hydrolysis of skin-relevant fatty acid epoxides and compared the products to those of acid-catalyzed hydrolysis. In the absence of enzyme, exposure to pH 5 or pH 6 at 37°C for 30 min hydrolyzed fatty acid allylic epoxyalcohols to four trihydroxy products. By contrast, human soluble EH [sEH (EPHX2)] and human or murine epoxide hydrolase-3 [EH3 (EPHX3)] hydrolyzed cis or trans allylic epoxides to single diastereomers, identical to the major isomers detected in epidermis. Microsomal EH [mEH (EPHX1)] was inactive with these substrates. At low substrate concentrations (<10 μM), EPHX2 hydrolyzed 14,15-epoxyeicosatrienoic acid (EET) at twice the rate of the epidermal epoxyalcohol, 9R,10R-trans-epoxy-11E-13R-hydroxy-octadecenoic acid, whereas human or murine EPHX3 hydrolyzed the allylic epoxyalcohol at 31-fold and 39-fold higher rates, respectively. These data implicate the activities of EPHX2 and EPHX3 in production of the linoleate triols detected as end products of the 12R-LOX pathway in the epidermis and implicate their functioning in formation of the mammalian water permeability barrier.