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Oxidative Properties of the Skin: A Determinant for Nickel Diffusion
Published in Jurij J. Hostýnek, Howard I. Maibach, Nickel and the Skin, 2019
Jurij J. Hostýnek, Katherine E. Reagan, Howard I. Maibach
Human skin features an acid mantle of pH 4 to 6 at the surface of the SC, which increases with depth to pH 7 at the juncture with live tissue (Öhman and Vahlquist, 1998). Determinants of this pH are protons, which gradually reach the surface of the skin, originating in the epidermis or as products of sebaceous gland activity. They stem from three classes of compounds: Amino acids, e.g., urocanic acid, pyrrolidone carboxylic acidAlpha-hydroxy acids, e.g., lactic and butyric acid, also present in sweatAcidic lipids, e.g., cholesteryl sulfate and free fatty acids, primarily oleic and linoleic (Elias, 1983; Lampe et al., 1983; Schurer and Elias, 1991).
Structure and Function of Human Skin
Published in Marc B. Brown, Adrian C. Williams, The Art and Science of Dermal Formulation Development, 2019
Marc B. Brown, Adrian C. Williams
On the surface of the stratum corneum, the acid mantle is a thin protective film comprised of sebum, corneocyte debris, and remnant material from sweat. Sebum is the principal component and is largely triglycerides, wax esters and squalene, though the composition and secretion of these differ by anatomical region. The mantle provides an acidic surface to the stratum corneum, in the region of pH 5 in comparison to the viable epidermis pH of around 7.4. The acid mantle thus provides a non-specific defence mechanism against the ingress of pathogenic organisms; if adapted to the slightly acid surface pH, once within the more alkaline environment of the viable epidermis, the pathogens are poorly adapted to survive. In terms of drug delivery, it is theoretically feasible that the acid mantle could affect the ionisation of applied drugs or that its lipids could provide an additional barrier to drug permeation, but in practice this very thin layer is seldom regarded as a significant obstacle to drug delivery.
Structure and function of skin
Published in Roger L. McMullen, Antioxidants and the Skin, 2018
While the precise role of sebaceous glands in skin has always mystified scientists, it undoubtedly plays an important role in the protection of the hair fiber and surface of the skin. As part of the pilosebaceous unit, the sebaceous gland opens up to the hair follicle canal, secreting its contents onto the surface of the fiber (Figure 1.8). Sebum lipids find their way to the surface and interior of the hair fiber, providing protection to its morphological components by reducing friction and wear. More than likely, lipids in the interior of the fiber probably serve as a reservoir, which are able to exude out onto the surface of the mature hair shaft when surface lipid levels are low. In addition, protection by sebum is conferred to the skin surface in the form of the acid mantle—a low pH film present on the surface of the skin that prevents microbial growth and invasion by foreign pathogens. It also helps protect skin from oxidation and in inflammation, and provides waterproofing properties rendering the skin surface hydrophobic with increased barrier function.47
Postoperative treatment after partial nail ablation of ingrown toenails — does it matter what we recommend? A blinded randomised study
Published in Scandinavian Journal of Primary Health Care, 2019
S. V. Bernardshaw, Liv Helene Dolva Sagedal, Kristin Møystad Michelet, Christina Brudvik
Although the growth of microorganisms was lower in the patients treated with acidic soap than in the other groups, the difference was not significant and did not correspond with clinical signs of infection. In a previous study it was found that washing with low pH soap influenced not only the pH on the skin surface in the short term, but also the cutaneous microflora in the long term [11]. The acid mantle of the skin plays an integral role in the function of the skin barrier as well as regulating the bacterial flora [11]. Other researchers have highlighted the negative effects of common cleaning agents and have even argued that normal tap water may have a negative effect on the skin surface [12]. Increasing the skin pH irritates the physiological protection of the acid mantle, changes the composition of the cutaneous bacterial flora and affects the activities of enzymes in the upper epidermis. Soaps with a pH of about 5.5, such as Lactacyd, appear to mimic the normal skin environment well, and, in contrast to alkaline soap, do not interfere with the cutaneous microflora [13]. The skin pH normally ranges from pH 4 to 6, and the normal bacterial flora is optimal at these slightly acidic pH levels, whereas pathogenic flora such as S. aureus thrive at neutral pH levels [14]. In this study, we found lower pathogenic growth in the Lactacyd group than in the other treatment groups (Table 3). However, our study was unable to confirm that the lower skin pH following acidic soap baths resulted in reduced clinical signs of infection.
Atopic dermatitis epidemiology and unmet need in the United Kingdom
Published in Journal of Dermatological Treatment, 2020
Michael J. Cork, Simon G. Danby, Graham S. Ogg
Bathing, by soaking in lukewarm water with emollients (and possibly short-term/intermittent antimicrobials), offers an opportunity to improve skin hydration, provides symptomatic relief of AD symptoms, and has an antipruritic effect (103,106). However, bathing can also cause dryness, especially if a harsh detergent is used. Therefore, non-soap-based cleansers and mild synthetic detergents (pH of 5.5–6.0) that protect the skin’s acid mantle are recommended for patients with AD (105).
The role of kallikreins in inflammatory skin disorders and their potential as therapeutic targets
Published in Critical Reviews in Clinical Laboratory Sciences, 2021
Caitlin T. Di Paolo, Eleftherios P. Diamandis, Ioannis Prassas
The epidermis is the most superficial and dynamic layer of the skin and is a highly ordered, avascular structure. It is made up of tightly packed keratinocytes in a stratified squamous epithelium. This stratified organization is maintained through the production and differentiation of keratinocytes and results in the formation of four (or five for thick skin, such as the palms of the hands and soles of the feet, which contain the stratum lucidum) distinct layers. The deepest layer of the epidermis, called the stratum basale (SB), is comprised of a layer of mitotically active cells that produce keratinocytes that will make up the more superficial layers. As the cells migrate upward, they become differentiated, undergo morphological changes, and begin to express desmosomal and cornified envelope (CE) components. Once in the stratum spinosum (SS), the cells will reinforce their cytoskeletal network with keratin filaments and undergo the final transition from keratinocytes to corneocytes prior to entry into the stratum granulosum (SG). At this point, the keratins are bundled in macrofibrils through association with filaggrin (FLG) and lipids are produced inside lamellar bodies. The tough CE is added to each cell through the integration of precursor proteins underneath the plasma membrane. The breakdown of the cell membrane causes a calcium influx, which activates the transglutaminase enzyme that will irreversibly cross-link the CE proteins [3]. An ordered intercellular lipid lamellae rich in ceramides is formed around the corneocytes, which taken together, act as the epidermal barrier and make up the final layer of the epidermis called the stratum corneum (SC) [4]. This barrier’s waterproof nature minimizes the transepidermal water loss (TEWL) and is essential for the effective physical barrier of the epidermis. Epidermal lipids, particularly ceramides, cholesterol, free fatty acids (FFAs), and triglycerides are key components to the formation and function of the epidermal permeability barrier [5]. Alterations in the lipid biosynthesis or metabolic pathways responsible for the lipids constituting the barrier will result in a destruction of barrier functionality [6]. Melanocytes and immune cells (i.e. Langerhan’s cells) are also found in the epidermis and participate in the skin immune barrier function. Additionally, the SC has a slightly acidic pH (4.5–6.5) which is called the acid mantle [7]. This decrease in pH is the result of secretions from sebaceous and sweat glands and functions to inhibit the growth of bacteria and fungi. It also plays a role in regulating the activity of numerous epidermal proteases.