The importance of free fatty acid chain length for the skin barrier function in atopic eczema patients

An important feature of atopic eczema (AE) is a decreased skin barrier function. The stratum corneum (SC) lipids – comprised of ceramides (CERs), free fatty acids (FFAs) and cholesterol – fulfil a predominant role in the skin barrier function. In this clinical study, the carbon chain length distribution of SC lipids (FFAs and CERs) and their importance for the lipid organization and skin barrier function were examined in AE patients and compared with control subjects. A reduction in FFA chain length and an increase in unsaturated FFAs are observed in non‐lesional and lesional SC of AE patients. The reduction in FFA chain length associates with a reduced CER chain length, suggesting a common synthetic pathway. The lipid chain length reduction correlates with a less dense lipid organization and a decreased skin barrier function. All changes are more pronounced in lesional SC compared with non‐lesional skin. No association was observed between lipid properties and filaggrin mutations, an important predisposing factor for developing AE. The results of this study demonstrate an altered SC lipid composition and signify the importance of these changes (specifically regarding the CER and FFA chain lengths) for the impaired skin barrier function in AE. This provides insights into epidermal lipid metabolism as well as new opportunities for skin barrier repair.     

Depletion of stratum corneum intercellular lipid lamellae and barrier function abnormalities after long-term topical corticosteroids

The intercellular lipid lamellae of the stratum corneum (SC) is believed to provide the permeability barrier of the epidermis. Previous functional studies have demonstrated an increase in the transepidermal water loss (TEWL) after long-term use of topical corticosteroids (TCS); however, direct morphological confirmation of this barrier abnormality is still lacking. The aim of this study was to determine whether any abnormality could be detected in the structure of the SC intercellular lipid lamellae in patients after long-term TCS. Atrophic skin and untreated normal skin of 10 patients after long-term TCS were examined by transmission electron microscopy using ruthenium tetroxide- fixed tissue for the multilamellar lipid sheets of SC, and oil red O stain for neutral lipids of the SC. Layers of the SC were evaluated by 0·1% methylene blue stain after alkaline expansion, and TEWL was measured by Evaporimeter EPI. The TCS-treated atrophic skin had fewer layers of horny cells, mean 9–4 layers, than the normal control skin, 18 layers (P<0·001) and increased TEWL of 21·3g/m² compared with the control skin TEWL of 6·7 g/m²(P<0·01). The mean neutral lipid content of the SC was also significantly lower (P<0·001). Moreover, ultrastructural studies revealed a marked decrease in both the numbers of intercellular lipid lamellae of SC and membrane-coating granules of stratum granulosum in the atrophic skin. These results suggest that the diminution in the SC intercellular lipid lamellae and SC cell layers play an important part in the pathogenesis of barrier dysfunction after long-term use of TCS.     

Topically applied fatty acids are elongated before incorporation in the stratum corneum lipid matrix in compromised skin

In several skin diseases, both the lipid composition and organization in the stratum corneum (SC) are altered which contributes to the impaired skin barrier function in patients. One of the approaches for skin barrier repair is treatment with topical formulations to normalize SC lipid composition and organization. Vernix caseosa (VC), a white cheesy cream on the skin during gestational delivery, has shown to enhance skin barrier repair. In this study, we examined how a fatty acid (FA) containing formulation mimicking the lipid composition of VC interacts with the lipid matrix in the SC. The formulation was applied on ex vivo human skin after SC removal. Subsequently, the ex vivo human skin generated SC during culture. The effect of FA containing formulations on the lipid organization and composition in the regenerated SC was analysed by Fourier transform infrared (FTIR) spectroscopy and liquid chromatography mass spectroscopy (LC/MS), respectively. FTIR results demonstrate that the FAs are intercalated in the lipid matrix of the regenerated SC and partition in the same lattice with the endogenous SC lipids, thereby enhancing the fraction of lipids forming an orthorhombic (very dense) packing in the SC. LC/MS data show that the topically applied FAs are elongated before intercalation in the lipid matrix and are thus involved in the lipid biosynthesis in the skin.     

Molecular interactions of plant oil components with stratum corneum lipids correlate with clinical measures of skin barrier function

Plant‐derived oils consisting of triglycerides and small amounts of free fatty acids (FFAs) are commonly used in skincare regimens. FFAs are known to disrupt skin barrier function. The objective of this study was to mechanistically study the effects of FFAs, triglycerides and their mixtures on skin barrier function. The effects of oleic acid (OA), glyceryl trioleate (GT) and OA/GT mixtures on skin barrier were assessed in vivo through measurement of transepidermal water loss (TEWL) and fluorescein dye penetration before and after a single application. OA's effects on stratum corneum (SC) lipid order in vivo were measured with infrared spectroscopy through application of perdeuterated OA (OA‐d₃₄). Studies of the interaction of OA and GT with skin lipids included imaging the distribution of OA‐d₃₄ and GT ex vivo with IR microspectroscopy and thermodynamic analysis of mixtures in aqueous monolayers. The oil mixtures increased both TEWL and fluorescein penetration 24 h after a single application in an OA dose‐dependent manner, with the highest increase from treatment with pure OA. OA‐d₃₄ penetrated into skin and disordered SC lipids. Furthermore, the ex vivo IR imaging studies showed that OA‐d₃₄ permeated to the dermal/epidermal junction while GT remained in the SC. The monolayer experiments showed preferential interspecies interactions between OA and SC lipids, while the mixing between GT and SC lipids was not thermodynamically preferred. The FFA component of plant oils may disrupt skin barrier function. The affinity between plant oil components and SC lipids likely determines the extent of their penetration and clinically measurable effects on skin barrier functions.     

Distinct barrier integrity phenotypes in filaggrin-related atopic eczema following sequential tape stripping and lipid profiling

Background Filaggrin gene (FLG) loss‐of‐function mutations have been shown to represent the strongest so far known genetic risk factor for atopic dermatitis (AD). Whereas the barrier characteristics in FLG mutation carriers under baseline conditions have been investigated, there are only limited data on the permeability barrier function in filaggrin‐AD under compromised conditions. Aim We investigated: (i) stratum corneum (SC) integrity/cohesion; (ii) barrier recovery after controlled mechanical and irritant‐induced barrier abrogation; and (iii) the lipid composition of the non‐lesional and lesional skin of AD patients harbouring the European R501X, 2282del4, 3702delG, R2447X or S3247X FLG variants. Methods Thirty‐seven AD patients (14 FLG mutation carriers and 23 non‐carriers) and 20 healthy controls participated in the study. Stratum corneum integrity/cohesion was assessed by measurement of transepidermal water loss (TEWL) and amount of removed protein following sequential tape stripping. Barrier recovery was monitored by repeated measurements of TEWL and erythema up to 96 h after barrier abrogation. Samples for lipid analysis were obtained from non‐lesional and lesional skin using the cyanoacrylate method. Results Tape stripping revealed distinct genotype‐related impairment of the SC integrity/cohesion. No differences in the rate of barrier recovery among the groups were found. The SC lipid analysis revealed significant differences regarding the percentage amount of cholesterol, ceramide/cholesterol ratio and triglycerides in the uninvolved skin as well as the amounts of free fatty acids, CER[EOH] and triglycerides in the skin lesions of the AD FLG mutation carriers. Conclusions Our results provide evidence for discernible FLG‐related barrier integrity phenotypes in atopic eczema.     

An ex vivo human skin model for studying skin barrier repair

In the studies described in this study, we introduce a novel ex vivo human skin barrier repair model. To develop this, we removed the upper layer of the skin, the stratum corneum (SC) by a reproducible cyanoacrylate stripping technique. After stripping the explants, they were cultured in vitro to allow the regeneration of the SC. We selected two culture temperatures 32°C and 37°C and a period of either 4 or 8 days. After 8 days of culture, the explant generated SC at a similar thickness compared to native human SC. At 37°C, the early and late epidermal differentiation programmes were executed comparably to native human skin with the exception of the barrier protein involucrin. At 32°C, early differentiation was delayed, but the terminal differentiation proteins were expressed as in stripped explants cultured at 37°C. Regarding the barrier properties, the SC lateral lipid organization was mainly hexagonal in the regenerated SC, whereas the lipids in native human SC adopt a more dense orthorhombic organization. In addition, the ceramide levels were higher in the cultured explants at 32°C and 37°C than in native human SC. In conclusion, we selected the stripped ex vivo skin model cultured at 37°C as a candidate model to study skin barrier repair because epidermal and SC characteristics mimic more closely the native human skin than the ex vivo skin model cultured at 32°C. Potentially, this model can be used for testing formulations for skin barrier repair.     

Determination of stratum corneum lipid profile by tape stripping in combination with high-performance thin-layer chromatography

Abstract Intercellular lipids in the stratum corneum (SC) are responsible for the barrier function of mammalian skin. The main components of the SC lipids are ceramides, cholesterol, and free fatty acids, as established by thin-layer chromatographic analysis of lipids extracted from the human and mammalian SC. Up to now, for lipid analysis the extracts of the entire SC has been used and information on whether the lipid composition changes with the depth in the SC is scarce. Tape stripping is a technique which removes corneocyte layers step by step with an adhesive film. The use of this technique for lipid analysis was hampered by the contamination of lipid extracts with compounds co-extracted from the tape with organic solvents used for the extraction of SC lipids. The aim of the present study was to establish a suitable analytical method for the determination of the local SC lipid composition. For this purpose, the SC samples were collected by sequential stripping with Leukoplex tape in five healthy volunteers. The lipids were extracted with ethyl acetate:methanol mixture (20:80) and separated by means of HPTLC. The results of this study revealed that the free fatty acid level is highest and the cholesterol and ceramide levels lowest in the uppermost SC layers (about 4 strippings). The levels remained unchanged in the underlying SC layers. In these layers, the ceramide level was about 60 wt% and the free fatty acid and cholesterol levels were about 20 wt% each. Ceramides could be separated into seven different fractions and the relative amounts of individual ceramide fractions did not significantly change with the SC depth. Cholesterol sulfate levels were about 5% of total cholesterol and did not change with the SC depth, except for the for the first strip where the level was about 1%. The method developed makes it possible to study the differences in the SC lipid profile in healthy and diseased human skin with relation to the SC lipid organization and to the skin barrier function in vivo. Received: 2 August 2000 / Revised: 20 December 2000 / Accepted: 26 January 2001     

Barrier function of intact and impaired skin: percutaneous penetration of caffeine and salicylic acid

Background Normally, percutaneous absorption tests are carried out using skin biopsies for an apparent and acceptable physiological condition. However, under different pathological conditions, the stratum corneum (SC) barrier function is impaired. Methods The barrier function of the SC was assessed by correlation between the number of repeated applications of tape strips on the skin and its transepidermal water loss (TEWL), as well as by in vitro percutaneous absorption studies of different compounds, using Franz diffusion cells and porcine skin previously stripped. Results A progressive diminution of the skin barrier function has been detected by TEWL both in vitro and in vivo as the number of skin tape strips increases. On the other hand, the percutaneous absorption of the compounds tested increases in a different way as the number of strips increases. Salicylic acid increases linearly depending on the barrier disturbance. However, percutaneous absorption of caffeine exponentially increased with barrier disturbance. Our results indicate that the barrier impairment of skin always increases the penetration behavior of a given compound; however, the hydrophilic–lipophilic balance of the compounds or formulations used could greatly modify its penetration profile, especially when a modified skin is used. Conclusions This in vitro protocol may be useful to simulate the percutaneous absorption profile of some drugs applied onto skin with an impaired SC barrier function and could be used to avoid, to some extent, the use of in vivo experimental animal models in the dermopharmaceutical field.     

Development of a stratum corneum and barrier function in an organotypic skin culture

The stratum corneum of human skin is responsible for maintaining the epidermal permeability barrier. We have developed a bilayered skin culture (SC) which forms a corneum 35 ± 1 cell layers thick 21 days after being raised to the air-liquid (A/L) interface. By the 7th day after raising to the A/L interface the corneocytes were irregularly shaped and had cross-sectional areas (CSA) of 300 m². By the 21st day the corneocytes had assumed polygonal shapes and had a CSA (100–250 m²) similar to that of human foreskin. The total lipid (TL) content of the corneum averaged 5–7% of the lyophilized weight. Ceramide content increased from 20% of TL at day 7 of A/L interface culture to 30% at day 21. Triglycerides decreased from 43% to 17% of TL during the same period. Free fatty acids comprised 5.5% of TL at day 21 of A/L interface culture. The intercorneocyte spaces contained stacks of lipid lamellae. However, the stacks lacked the Landmann unit repeat. Abnormal lamellar structures were observed in both the intra- and extracorneocyte spaces. Transepidermal water loss (TEWL) was >4 mg/cm² per h throughout the culture period. Lipid supplementation of the culture medium and culturing in a low humidity environment improved barrier function by 50%. However, the effects were not additive. The SC developed a near-normal corneum, but did not achieve barrier competence, due at least partially to abnormalities in lipid composition and organization. Improvement of barrier function with lipid supplementation or low humidity indicates that modifications of the culture environment may facilitate the SC in assembling a permeability barrier equivalent to human skin.     

SKIN SURFACE LIPIDS IN HIV-POSITIVE PATIENTS WITH AND WITHOUT SEBORRHEIC DERMATITIS

Background. Seborrheic dernnatitis (SD) is a frequent complication of infection with the human immunodeficiency virus (HIV). Most studies examining the cause of SD have concentrated on the roles of Pityrosporum ovale and sebaceous lipids. Previous studies of skin surface lipid from patients with SD have produced conflicting results, with some authors reporting an abnormal lipid composition and others finding little or no abnormality. Methods. The composition of skin surface lipid was studied in 15 HIV-positive and 10 HIV-negative men with SD, in 14 HIV-positive men without SD, and in 16 unaffected controls. Total lipids were extracted from unaffected forehead skin into petroleum ether and separated into lipid classes by thin layer chromatography. The lipid classes were quantitated by densitometry after charring with sulfuric acid. Results. Patients, HIV-positive with SD, had significantly lower proportions of free fatty acid (FFA) and higher levels of triglyceride than normal controls. Patients, HIV-positive without SD, had a significantly increased proportion of FFA compared to HIV-positive patients with SD. Patients with SD, both HIV-positive and HIV-negative, had a similar pattern of skin surface lipid. Levels of FFA were lower and those of triglyceride higher than in the patients unaffected by SD, whether HIV-positive or not. There was no significant difference found between groups in free cholesterol, wax esters, and squalene. Conclusions. Abnormalities of skin surface lipid composition may play a part in the development of SD in both HIV-positive and HIV-negative men.     

Knock‐down of filaggrin does not affect lipid organization and composition in stratum corneum of reconstructed human skin equivalents

Human skin mainly functions as an effective barrier against unwanted environmental influences. The barrier function strongly relies on the outermost layer of the skin, the stratum corneum (SC), which is composed of corneocytes embedded in an extracellular lipid matrix. The importance of a proper barrier function is shown in various skin disorders such as atopic dermatitis (AD), a complex human skin disorder strongly associated with filaggrin (FLG) null mutations, but their role in barrier function is yet unclear. To study the role of FLG in SC barrier properties in terms of SC lipid organization and lipid composition, we generated an N/TERT‐based 3D‐skin equivalent (NSE) after knock‐down of FLG with shRNA. In these NSEs, we examined epidermal morphogenesis by evaluating the expression of differentiation markers keratin 10, FLG, loricrin and the proliferation marker ki67. Furthermore, the SC was extensively analysed for lipid organization, lipid composition and SC permeability. Our results demonstrate that FLG knock‐down (FLG‐KD) did not affect epidermal morphogenesis, SC lipid organization, lipid composition and SC permeability for a lipophilic compound in NSEs. Therefore, our findings indicate that FLG‐KD alone does not necessarily affect the functionality of a proper barrier function.     

Surfactants have multi-fold effects on skin barrier function

Background

The stratum corneum (SC) is responsible for the barrier properties of the skin and the role of intercorneocyte skin lipids, particularly their structural organization, in controlling SC permeability is acknowledged. Upon contacting the skin, surfactants interact with the SC components leading to barrier damage.

Objective

To improve knowledge of the effect of several classes of surfactant on skin barrier function at three different levels.

Methods

The influence of treatments of human skin explants with six non-ionic and four ionic surfactant solutions on the physicochemical properties of skin was investigated. Skin surface wettability and polarity were assessed through contact angle measurements. Infrared spectroscopy allowed monitoring the SC lipid organization. The lipid extraction potency of surfactants was evaluated thanks to HPLC-ELSD assays.

Results

One anionic and one cationic surfactant increased the skin polarity by removing the sebaceous and epidermal lipids and by disturbing the organization of the lipid matrix. Another cationic surfactant displayed a detergency effect without disturbing the skin barrier. Several non-ionic surfactants disturbed the lipid matrix organization and modified the skin wettability without any extraction of the skin lipids. Finally two non-ionic surfactants did not show any effect on the investigated parameters or on the skin barrier.

Conclusions

The polarity, the organization of the lipid matrix and the lipid composition of the skin allowed describing finely how surfactants can interact with the skin and disturb the skin barrier function.

     

Effects of CO<Subscript>2</Subscript>-enriched water on barrier recovery

The objective of the present study was to evaluate the impact of CO₂-enriched water on barrier recovery of detergent-damaged skin compared to tap water employing bioengineering methods and thin-layer chromatography (TLC) analysis of stratum corneum (SC) lipids. Irritation of the skin was elicited on the forearms of 20 volunteers using 1% sodium lauryl sulphate (SLS). The degree of skin irritation was followed over 10 days in terms of skin colour reflectance (L*a*b*), transepidermal water loss (TEWL), and skin capacitance expressed as median values. For TLC analysis, SC lipids were extracted prior to and during the observation period. Clinical examination showed the efficacy of CO₂-enriched water on barrier recovery. Compared to unenriched tap water, CO₂-enriched water produced a significant (P<0.01) increase in total SC lipids and in particular in the ceramide fraction. Furthermore, TEWL was significantly (P<0.01) lower in skin treated with CO₂-enriched water than in skin treated with unenriched water. These findings may indicate that rinsing with CO₂-enriched water enhances (1) clinical regeneration of detergent-damaged skin, (2) epidermal lipid synthesis, and (3) barrier repair after detergent-induced perturbation.     

Non‐invasive assessment of tryptophan fluorescence and confocal microscopy provide information on skin barrier repair dynamics beyond TEWL

The stratum corneum (SC) serves a primary function of skin barrier and understanding the kinetics of SC formation may provide great insight for skin diagnosis and evaluation of therapies. Besides trans‐epidermal water loss (TEWL), few methods have been characterized to assess skin barrier non‐invasively in vivo, particularly for dynamic measurements on the same specimen over time. The objective of this study was to characterize alternative non‐invasive methods to evaluate the dynamic processes involved in the recovery of normal human SC after total removal. TEWL, tryptophan fluorescence and reflectance confocal microscopy (RCM) were used to determine skin barrier function, cell turnover and epidermal morphology over a period of 10 days after total removal of the SC by tape stripping. The results show a biphasic recovery of TEWL over time, which contrasted with a linear increase of 2.3 μm/day in SC thickness. Tryptophan assessment of cell turnover also demonstrated a biphasic pattern attaining a maximum three to four times the levels of the control site 3 days after injury that slowly returned to baseline and displayed great correlation (R² > 0.95) to viable epidermis thickness that also achieved a maximum about 3 days after injury with an approximate increase of 55%. When plotting the change of TEWL versus SC thickness, a single exponential function is observed [Δ‐TEWL = 55 exp (?0.157×)] which contrasts with other proposed models. These methods were able to present rates for SC recovery processes beyond skin barrier (TEWL) that may provide new insights on kinetics of barrier formation for evaluation of skin conditions and treatments.     

The lipid alterations in the stratum corneum of dogs with atopic dermatitis are alleviated by topical application of a sphingolipid-containing emulsion

Background. Atopic dermatitis (AD) results from an altered skin barrier associated with defects in the lipid composition of the skin. Dogs with AD present similar clinical symptoms to humans, and may be a useful model for investigations into AD. Aim. To analyse the changes occurring in the lipids of the stratum corneum (SC) of dogs with AE after 3 weeks of topical treatment with an emulsion containing ceramides, free fatty acids (FFAs) and cholesterol (skin lipid complex; SLC). Methods. Nonlesional SC was collected by tape stripping from control and treated areas. Free and protein‐bound lipids were purified, and the various classes were isolated by column chromatography, analysed by thin‐layer chromatography and assayed. Results. Ceramides, FFA and cholesterol were all found to be lower in the skin of untreated dogs with AD than in normal dogs, and the topical treatment resulted in significantly increased values for ceramides. Conversely, only trace amounts of glucosylceramides were present in normal SC, but a high concentration (27 μg per mg protein) was detected in canine atopic SC, which disappeared after treatment with SLC. There was a heterogeneous distribution of all of the lipids in the different layers of canine atopic SC, which was more pronounced for protein‐bound than for free lipids. Following topical treatment, the protein‐bound lipid content normalized. Conclusions. Topical treatment with SLC resulted in a significant improvement of the lipid biosynthesis of keratinocytes in atopic dogs, thereby potentially enabling the formation of a tighter epidermal barrier.     

Barrier function in reconstructed epidermis and its resemblance to native human skin

One of the prerequisites for the use of human skin equivalents for scientific and screening purposes is that their barrier function is similar to that of native skin. Using human epidermis reconstructed on de-epidermized dermis we demonstrated that the formation of the stratum corneum (SC) barrier in vitro proceeds similarly as in vivo as judged from the extensive production of lamellar bodies, their complete extrusion at the stratum granulosum/SC interface, and the formation of multiple broad lamellar structures in the intercorneocyte space. The presence of well-ordered lipid lamellar phases was confirmed by small-angle X-ray diffraction. Although the long periodicity lamellar phase was present in both the native and the reconstructed epidermis, the short periodicity lamellar phase was present only in native tissue. In addition, the SC lipids predominantly formed the hexagonal sublattice. Analysis of lipid composition revealed that all SC lipids are synthesized in vitro. Differences in SC lipid organization in reconstructed epidermis may be ascribed to the differences in fatty acid content and profile indicating that further improvement in culture conditions is required for generation of in vitro reconstructed epidermis with stratum barrier properties of the native tissue.     

Barrier recovery is impeded at neutral pH, independent of ionic effects: implications for extracellular lipid processing

β-glucocerebrosidase (β-GlcCer’ase), which exhibits a distinct acidic pH optimum, is particularly well documented. Therefore, we sought to determine whether the recovery of the barrier after acute insults requires acidification of the SC. We examined permeability barrier recovery by assessing changes in transepidermal water loss (TEWL), SC membrane ultrastructure utilizing ruthenium tetroxide (RuO ₄ ) postfixation, and β-GlcCer’ase activity by in situ zymography at an acidic vs neutral pH. Barrier recovery proceeded normally when acetone-treated skin was exposed to solutions buffered to an acidic pH. In contrast, the initiation of barrier recovery was slowed when treated skin was exposed to neutral or alkaline pH, regardless of buffer composition. In addition, enhancement of the alkaline buffer-induced delay in barrier recovery occurred with Ca ²⁺ and K ⁺ inclusion in the buffer. Moreover, the pH-dependent alteration in barrier recovery appeared to occur through a mechanism that was independent of Ca ²⁺ - or K ⁺ -controlled lamellar body secretion, since both the formation and secretion of lamellar bodies proceeded comparably at pH 5.5 and pH 7.4. In contrast, exposure to pH 7.4 (but not pH 5.5) resulted in both the persistence of immature, extracellular lamellar membrane structures, and a marked decrease in the in situ activity of β-GlcCer’ase. These results suggest first that an acidic extracellular pH is necessary for the initiation of barrier recovery, and second that the delay in barrier recovery is a consequence of inhibition of postsecretory lipid processing. Received: 16 June 1997     

Apolipoprotein ε4 allele is associated with psoriasis severity

Many reports provided strong evidence of the influence of genetic factors in the pathogenesis of psoriasis (Ps). A higher prevalence of lipid disorders in psoriatic patients has been reported. Because apolipoprotein E (apoE) is involved in lipid metabolism, APOE gene variants could be candidates to influence Ps-risk. However, data about the potential influence of the APOE genotypes in Ps are inconclusive. Our objective was to investigate the relationship between the common APOE-ε2/ε3/ε4 variation and Ps in a Caucasian population. Our study involved 331 unrelated Ps-patients and 400 healthy controls. Patients and controls were genotyped for the APOE-ε2/ε3/ε4 polymorphism, and allele and genotype frequencies were statistically compared between the two groups and between patients according to disease severity. Mean lipid values were also compared between the APOE genotypes. Allele and genotype frequencies did not differ between patients and controls. APOE-ε4 carriers were significantly more frequent in patients with severe Ps compared to controls (P = 0.003) and to non-severe Ps (P = 0.017). No significant difference in mean lipid values was found between the APOE genotypes. The APOE-ε4 allele could be a risk factor for developing a severe form of psoriasis.     

Infant epidermal skin physiology: adaptation after birth

Background Functional and structural skin adaptation is a dynamic process which starts immediately after birth in humans and in mammalian skin in general. This adjustment to the extrauterine dry environment is accomplished in the first year of postnatal life of humans. Objectives To assess the dynamic changes in vivo after birth in the molecular composition and skin physiology parameters compared with older children and adults. Methods The molecular composition of the stratum corneum (SC) and the water profile were investigated noninvasively by in vivo Raman confocal microscopy as a function of depth. Functional parameters including transepidermal water loss (characterizing epidermal permeability barrier), capacitance (as an indirect parameter for SC hydration) and skin surface pH were assessed noninvasively. The measurements were performed in 108 subjects divided into six age groups: full‐term newborns (1–15 days), babies aged 5–6 weeks, babies aged 6 ± 1 months, children aged 1–2 years, children aged 4–5 years and adults aged 20–35 years. Results We showed that skin acidification is still under development during the first weeks of life. While the basal epidermal barrier is competent immediately after birth, the SC is less hydrated in the first 2 weeks of postnatal life. Similar continuous decreasing water content towards the surface for all age groups was observed, whereas this gradient was lower for the newborns. Dynamic changes in the amounts of the natural moisturizing factor constituents were revealed in the period of infancy. Conclusions 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.