Glycerol is a trihydroxy alcohol that has been included for many years in topical dermatological preparations. In addition, endogenous glycerol plays a role in skin hydration, cutaneous elasticity and epidermal barrier repair. The aquaporin-3 transport channel and lipid metabolism in the pilosebaceous unit have been evidenced as potential pathways for endogenous delivery of glycerol and for its metabolism in the skin. Multiple effects of glycerol on the skin have been reported. The diverse actions of the polyol glycerol on the epidermis include improvement of stratum corneum hydration, skin barrier function and skin mechanical properties, inhibition of the stratum corneum lipid phase transition, protection against irritating stimuli, enhancement of desmosomal degradation, and acceleration of wound-healing processes. Even an antimicrobial effect has been demonstrated. Topical application of glycerol-containing products improves skin properties in diseases characterized by xerosis and impaired epidermal barrier function, such as atopic dermatitis. The increase of epidermal hydration by glycerol is critical in skin conditions aggravated by dry and cold environmental conditions, e.g. winter xerosis. This paper provides a review on effects of glycerol on the skin, the mechanisms of its action, and the potential applications of glycerol in dermatology.

Journal Pre-proof J o u r n a l P r e -p r o o f 2 Running title: COVID-19 and the skin Conflict of interests: none Funding sources: none Acknowledgements: none Journal Pre-proof J o u r n a l P r e -p r o o f 3 AbstractThe World has changed dramatically since the COVID-19 pandemic began. Together with our social, occupational, and personal life, the new corona virus poses novel challenges for all physicians, including dermatologists. Despite the virus not being dermatotropic, several skin conditions have emerged, mainly as a result of prolonged contact to personal protective equipment and excessive personal hygiene. Pressure injury, contact dermatitis, itch, pressure urticaria, and exacerbation of pre-existing skin diseases, including seborrheic dermatitis and acne, have been described. We have focused on the dermatologic aspects of COVID-19 infection, so that dermatologist may be aware of the skin complications and the preventive measures to be taken in the COVID-19 pandemic. Abbreviations:healthcare workers -HCWs personal protective equipment -PPE Journal Pre-proof identified as the most common entry for the infection, this includes the conjunctiva with the otic canal having the lowest risk of transmission (4); therefore, specific skin changes due to Covid-19 infection have not been described, and one could expect iatrogenic secondary involvement of the skin.Journal Pre-proof J o u r n a l P r e -p r o o f 5 Because diseases with epidermal barrier interruption could enhance the virus acquisition through indirect contact (5), dermatology patients might be at an increased risk for developing the infection. This suggests that dermatology departments and private offices should develop appropriate preventative measures. (5). Use of a sanitary mask itself may not be sufficient protection from the virus transmission, so that goggles should be used to decrease the risk of conjunctival contamination. COVID-19 has a relatively low-resistance to disinfectants. As a result, a variety of regimens have been proven effective, ranging from 75% ethanol, peracetic acid, chlorine, and UV disinfection to a hot water bath at 56°C(132.8°F) for 30 minutes (4).Another important practical concern is the care for patients with autoimmune and chronic inflammatory disorders, such as psoriasis, atopic dermatitis, lupus, scleroderma, and hidradenitis suppurativa, which may require immune-suppressive therapy. It is not clear whether the administration of the biologics should be delayed. Skin problems related to personal protective equipment (PPE) and personal hygiene measuresThe skin complications in COVID-19 infection are mainly due to the hyper-hydration effect of PPE, friction, epidermal barrier breakdown, and contact reactions, all of which may aggravate an existing skin disease. The dermatologic manifestations are far different from those recorded during the Influenza Epidemic of 1918-1919 (6). Erythema, papules, maceration, and scaling are the most commonly reported skin changes due to extended wear of PPE (6) (figure 1).Symptoms have...

We demonstrated the relation of formation of an acidic pH as well as underlying mechanisms in the induction of a fully hydrated SC over the first weeks of human life as a dynamic functional adaptation.

Early postnatal life is a period of active functional reorganization and cutaneous physiological adaptation to the extrauterine environment. Skin as the outermost organ of mammalians is endowed of multiple functions such as protection, secretion, absorption and thermoregulation. Birth stimulates the epidermal barrier maturation and the skin surface acidification especially in premature infants. In full-term infants the developed stratum corneum accomplishes competent barrier function, in contrast to prematures. Complete barrier maturation in preterm infants is fulfilled by 2-4 weeks of the postnatal life. However, in preterms with 23-25 weeks gestational age this process takes longer. Versatile regulatory mechanisms, namely skin surface acidity, calcium ion gradient and nuclear hormone receptors ⁄ ligands are interrelated in the complex postnatal newborn adaptation. The skin of newborns is adjusting quickly to the challenging environmental conditions of the postpartum.However, certain functions, for example, microcirculation, continue to develop even beyond the neonatal period, that is, up to the age of 14-17 weeks. Different environmental factors (for instance, dry and cold climate, diapers and cosmetic care procedures) influence the postnatal development of skin functional parameters such as stratum corneum hydration and the permeability barrier especially in premature infants. The aim of this article is to summarize the current knowledge on skin physiology in newborn and infants with a practical approach and to discuss the possible clinical consequences. This review offers the readership a critical and practical overview of skin physiology in newborns and infants. It emphasizes possible new research fields in neonatal and infantile skin physiology.

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Background/Aim: The skin, as the outermost organ, protects against exogenous hazards (outside-in barrier) and prevents the loss of essential parts of the body (inside-out barrier). The epidermal barrier exerts several functions with specific morphological elements. Regional differences in skin functions are well known. The aim of the present study was to assess and compare skin physiological parameters in vivo at 16 anatomical sites: Barrier function in terms of transepidermal water loss (TEWL), stratum corneum (SC) hydration (assessed by capacitance), skin surface pH, skin surface temperature, erythema index and skin pigmentation were quantified at 16 anatomical sites under basal conditions. In addition, casual skin lipid level as a function of sebaceous lipids was measured on the forehead. Material and Methods: The 6 functions at the 16 anatomical sites were assessed in a cohort of 125 volunteers working in the food processing industry. These functions were quantified with noninvasive instruments, namely a Tewameter (barrier function), a Corneometer (SC hydration), a pH-meter, a Mexameter (erythema index and pigmentation), a skin surface thermometer and a Sebumeter (casual sebum level). Results: We identified ranges for the 16 anatomical locations for each instrument and some parameters could be classified into distinctive groups. Furthermore, a left-right comparison was performed at 3 sites (dorsal hand, ventral hand and ventral forearm). Certain side differences could be shown for SC hydration, surface pH, erythema index, melanin index and skin surface temperature in the 3 assessed areas. A left-to-right, statistically nonsignificant difference was also established for TEWL. Conclusion: The detected site-specific characteristics could be attributed to factors such as occlusion, different degrees of UV exposure, microcirculation and distribution of afferent and efferent nerve endings as well as fat distribution. External factors, such as life style, UV exposure and working conditions need to be taken into account. The present data are intended for an adequate selection of parameters and anatomical locations when assessing working conditions and designing clinical dermatological and pharmaceutical studies.

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The aim of the study was to disclose interactions between epidermal barrier, skin irritation and sensitization in healthy and diseased skin. Transepidermal water loss (TEWL) and stratum corneum hydration (SCH) were assessed in adult patients with atopic dermatitis (AD), rosacea and healthy controls. A 4-h patch test with seven concentrations of sodium lauryl sulphate was performed to determine the irritant threshold (IT). Contact sensitization pattern was revealed by patch testing with European baseline series. Subjects with a lower IT had higher TEWL values and lower SCH. Subjects with positive allergic reactions had significantly lower IT. In AD, epidermal barrier deterioration was detected on both volar forearm and nasolabial fold, while in rosacea, impeded skin physiology parameters were observed on the facial skin only, suggesting that barrier impediment is restricted to the face in rosacea, in contrast with AD where the abnormal skin physiology is generalized.