Medical expert of the article
New publications
Peculiarities of skin barrier properties
Last reviewed: 08.07.2025
All iLive content is medically reviewed or fact checked to ensure as much factual accuracy as possible.
We have strict sourcing guidelines and only link to reputable media sites, academic research institutions and, whenever possible, medically peer reviewed studies. Note that the numbers in parentheses ([1], [2], etc.) are clickable links to these studies.
If you feel that any of our content is inaccurate, out-of-date, or otherwise questionable, please select it and press Ctrl + Enter.
The barrier properties of the skin, which determine the body's protection from the effects of external factors, are provided by the complex interaction of the stratum corneum, highly specialized lipids of the stratum corneum, and the water-lipid mantle.
The stratum corneum provides mechanical protection of the skin from external damage. Due to the constant exfoliation of horny scales, the skin surface is cleansed. The thickness of the stratum corneum varies from 9 µm (skin of the eyelids) to 0.5 cm (skin of the palms and soles) and depends on the anatomical location.
A delicate balance is established on the skin surface between the water content in the stratum corneum itself and in the surrounding environment. To maintain normal hydration of the stratum corneum, there is a unique structure that is rightly compared by many researchers to a brick wall, where the role of "bricks" is played by corneocytes (postcellular structures of the stratum corneum), and the "cement" is highly specialized and uniquely organized intercellular lipids. Such lipids include, first of all, ceramides, cholesterol, fatty acids, as well as phospholipids, glycosylceramides, free sphingoid bases and cholesterol sulfate.
It is currently known that the stratum corneum of the epidermis contains six main classes of so-called "free" ceramides, not bound to corneocytes, and two main classes of ceramides covalently bound to the surface of corneocytes (classes A and B). The composition of ceramides in the stratum corneum of the skin in humans is highly variable and depends on race, concomitant somatic diseases, age, environment and a number of other factors. Ceramides have a rather complex chemical structure. Most of them are long chains of sphingoid bases with the number of carbon atoms from 16 to 22, less often they are represented by dihydrosphingosine, phytosphingosine and 6-hydroxysphingosine. Sphingoid bases are linked to various fatty acids, including free lower fatty acids, which perform a number of important biological functions (oleic, linoleic, etc.). The functions of ceramides include not only water retention in the skin, but also regulation of the rate of desquamation, as well as influence on the differentiation of keratinocytes. It has been shown that sphingosine is able to regulate the rate of renewal of the epithelial layer, preventing its rapid replacement without normal differentiation of keratinocytes. Recent studies have shown that sphingosine is also a fairly strong antimicrobial agent, and its presence in the epidermal layer provides protection from microorganisms on the skin surface.
Synthesis of many lipids, including ceramides, is carried out in special organelles of granular layer cells - lamellar bodies, later these substances form bilipid layers between corneocytes. These lipids form the main barrier for water, thereby preventing transepidermal water loss (TEWL). They also play the role of a special intercellular cementing substance, providing strength of adhesion of postcellular structures of the stratum corneum and ensuring the integrity of the skin. The functions of ceramides include not only water retention in the skin, but also regulation of the rate of desquamation, influence on keratinocyte differentiation, and antimicrobial action.
The skin surface is covered with a continuous thin water-fat emulsion film - the water-lipid mantle. It consists of the secretion of the sebaceous glands, eccrine sweat glands and ceramides of the stratum corneum. The water-lipid mantle prevents skin drying, regulates the rate of desquamation and differentiation of keratinocytes, maintains constant acidity of the skin surface (pH 4.5-5.5), and is also one of the ways of excretion of metabolic products, medicinal and toxic substances. Depending on the ratio of sebum and sweat on the skin, the resulting water-lipid emulsion can contain more fat (type "water in oil") or more water (type "oil in water"), which ensures a constant body temperature.
[ 1 ], [ 2 ], [ 3 ], [ 4 ], [ 5 ], [ 6 ], [ 7 ], [ 8 ], [ 9 ], [ 10 ], [ 11 ], [ 12 ]