Location‐related differences in structure and function of the stratum corneum with special emphasis on those of the facial skin

Abstract

Between the two different kinds of the skin covering the body, the glabrous skin is found only on the palmo-plantar surface because of its rather simple function to protect the underlying living tissue with its remarkably thick stratum corneum (SC) from strong external force and friction. Thus, its barrier function is extremely poor. In contrast, the hair-bearing skin covers almost all over the body surface regardless of the presence of long hair or vellus hair. In regard to its SC, many dermatologists and skin scientists think that it is too thin to show any site-specific differences, because the SC is just present as an efficient barrier membrane to protect our body from desiccation as well as against the invasion by external injurious agents. However, there are remarkable regional differences not only in the living skin tissue but also even in such thin SC reflecting the function of each anatomical location. These differences in the SC have been mostly disclosed with the advent of non-invasive biophysical instruments, particularly the one that enables us to measure transepidermal water loss (TEWL), the parameter of the SC barrier function, and the one that evaluates the hydration state of the skin surface, the parameter of the water-holding capacity of the SC that brings about softness and smoothness to the skin surface. These in vivo instrumental measurements of the SC have disclosed the presence of remarkable differences in the functional properties of the SC particularly between the face and other portions of the body. The SC of the facial skin is thinner, being composed of smaller layers of corneocytes than that of the trunk and limbs. It shows unique functional characteristics to provide hydrated skin surface but relatively poor barrier function, which is similar to that observed in retinoid-treated skin or to that of fresh scar or keloidal scars. Moreover, there even exist unexpected, site-dependent differences in the SC of the facial skin such as the forehead, eyelid, cheek, nose and perioral regions, although each location occupies only a small area. Between these locations, the cheek shows the lowest TEWL in contrast to the perioral region that reveals the highest one. Moreover, these features are not static but change with age particularly between children and adults and maybe also between genders. Among various facial locations, the eyelid skin is distinct from others because its SC is associated with poor skin surface lipids and a thin SC cell layer composed of large corneocytes that brings about high surface hydration state but poor barrier function, whereas the vermillion borders of the lips that are covered by an exposed part of the oral mucosa exhibit remarkably poor barrier function and low hydration state. Future studies aiming at the establishment of the functional mapping in each facial region and in other body regions will shed light on more delicate site-dependent differences, which will provide us important information in planning the strategy to start so called tailor-made skin care for...

A systematic literature review of the human skin microbiome as biomarker for dermatological drug development

“…This, along with the human genome, completes what is now termed the human microbial superorganism 5. The skin microbiome harbours vast microbial communities living in a range of both physiologically and topographically distinct niches and microenvironments 6, 7. Actinobacteria (52%), Firmicutes (24%), Proteobacteria (17%) and Bacteroidetes (7%) are the four most abundant species identified on the skin 8.…”

Expert opinion and review article: The timing of comedone extraction in the treatment of premenstrual acne – a proposed therapeutic approach

“…The face has distinct facial zones to which specific concerns are aligned [56]. In general, comedones and acne develop at the T-zone, the area rich in sebaceous glands comprising the central part of the forehead, the nose, para-nasal part of the cheeks, the perioral area and the chin.…”

“…The T-zone exhibits the characteristics of oily skin, and its shiny appearance and high sebum levels are caused by the overproduction of the sebaceous glands. The chin in particular is prone to acne because of its poor skin barrier function [57] signified by the presence of smaller corneocytes and further aggravated by the sebum being transformed into unsaturated free fatty acids [56].…”

Mycobiota: Micro-Eukaryotes Inhabiting Our Body as Commensals or Opportunistic Pathogens

“…Culture-dependent approaches have identified many commensal fungi that are present on the skin, with Malassezia as the most common genus, followed by Penicillium and Aspergillus [38,62,65]. Other fungi, such as Alternaria, Candida, Rhodotorula and Cladosporium, have also been cultured but with a lower frequency [38,64,65]. Culture-independent sequencing studies have confirmed that the genus Malassezia is most commonly represented on healthy human skin across different body sites [38,48,66].…”

“…Deep sequencing approaches have demonstrated that the healthy skin contains a unique bacterial and fungal microbiota [30,38,[62][63][64]. The composition of this microbial community depends on physiologic attributes and topography of the skin, with certain patterns being associated with moist, dry or sebaceous microenvironments [30,62].…”