Minimal erythema dose in UV-shielded and UV-exposed skin predicted by skin reflectance measured pigmentation

Aims: To investigate the relationships between epidermal thickness, age, skin pigmentation and UV sensitivity in sun-exposed skin and skin not exposed to the sun in healthy people without skin cancer or skin diseases. Methods: Phototesting with a xenon arc solar simulator was performed in 137 healthy Caucasians in buttock skin un-exposed to UV (27 children, 34 young adults and 32 older adults) and in skin of the back exposed to UV (44 young adults). The pigmentation of the phototest sites was measured objectively by a skin reflectance spectrometer before phototesting. Thickness of the stratum corneum and the cellular epidermis were measured in skin biopsies from the phototest sites. All measurements were performed in the winter and spring months. Results: Stratum corneum and cellular epidermis were thinner at the back than at the buttocks (P<0.01). Thickness of the stratum corneum at the back or the buttocks was not related to the degree of skin pigmentation (P=0.62 and P=0.20, respectively). Thickness of the stratum corneum at the buttocks was unaffected by gender (P=0.42) and age (P=0.83) whereas cellular epidermis decreased with age (P<0.01) and was thinner in females than in males (P<0.01). In spite of the higher pigmentation at the back than at the buttocks, the minimal erythema dose (MED) was lower at the back than at the buttocks (x=2.7 and x=2.2 SED's, respectively; P=0.04). Given the same degree of skin pigmentation, there was no difference in the MED in buttock skin in children, young adults and older adults un-exposed to UV (P= 0.61). Prediction of the MED in un-exposed buttock skin and in exposed skin of the back by a theoretical model based on an exponential function of the measured skin pigmentation was found to provide good estimates of the MED determined by phototest. Conclusion: Skin pigmentation at un-exposed buttock skin can reliably predict the constitutive UV sensitivity in healthy Caucasian children and adults and is recommended in surveys where phototesting cannot be performed.     

Fitzpatrick皮肤分型和最小红斑量

Fitzpatrick皮肤分型是依据皮肤经一定剂量的日光照射后产生红斑还是色素及其程度,可分为6型.最小红斑量是评价皮肤分型的最重要的参数.理论上,根据光皮肤分型和最小红斑量的定义,随着光皮肤类型的增加,最小红斑量倾向于增加.然而,个体间自然光防护能力的差异,影响角质层厚度和黑素含量的基因方面因素,未曝光的部位肤色及测定最小红斑量的方法、部位等的不同,均使得两者的关系至今也尚不明确.概述近年来Fitzpatrick皮肤分型和最小红斑量的相关性研究进展.     

Melanin differentially protects from the initiation and progression of threshold UV-induced erythema depending on UV waveband

BACKGROUND/PURPOSE: This study aimed to determine the relationship between various measures of constitutive skin pigmentation and erythema caused by solar-simulated UV (ssUV), 290 and 310 nm UV. METHODS: Skin pigmentation was assessed clinically by skin typing as well as objectively by measurement of the melanin index (MI) by reflectance spectroscopy. Subjects having Fitzpatrick skin types I-IV were exposed to graded doses of ssUV and either narrowband 310 nm (n=70) or 290 nm (n=69) UV, and assessed 24 h after exposure. Minimal erythema dose (MED) was assessed visually as the lowest dose that caused minimally perceptible erythema. Susceptibility to further development of erythema with higher exposure doses was measured by the gradient of erythema dose-response curves. This was determined by linear regression using reflectance spectrometry data beyond the MED. RESULTS: Although there was considerable variation within each skin type, MI and ssUV MED increased with increasing Fitzpatrick skin type. MI correlated with ssUV MED and 310 nm UV MED, but not 290 nm UV MED. There was also a significant negative correlation between MI and erythema dose-response gradients caused by ssUV, 310 and 290 nm UV. CONCLUSION: Melanin situated near the basal epidermis may not protect from the initial development of threshold erythema caused by 290 nm UV because it penetrates poorly past the stratum corneum and is not well absorbed by melanin in vivo compared with 310 nm UV. Higher erythemal 290 nm UV doses may reach basal epidermal melanin, which may then afford protection against further 290 nm UV erythema.     

The Caucasian and African skin types differ morphologically and functionally in their dermal component

Abstract:  In the literature, most reported differences between African and Caucasian skin properties concern pigmentation and barrier function of the stratum corneum and related photoprotective properties. However, little is known about differences in morphology and possibly related biological functions. In this study, we investigated: (i) architectural differences of Caucasian and African mammary skin biopsies using microscopy, (ii) comparative constitutive expression of cytokines, matrix metalloproteinase 1 (MMP-1) and its inhibitors in papillary dermal fibroblast (pF) and reticular dermal fibroblast (rF) cultures in order to reveal biological features. (i) Neither epidermis thickness nor superficial dermis thickness was significantly different in African versus Caucasian subjects. However, the dermal–epidermal junction (DEJ) length in African skin was about threefold that in Caucasian skin. No differences were noticed as regards elastic and collagen fibre organization. (ii) In papillary fibroblast cultures, a significantly higher level of monocyte chemotactic peptide-1 (MCP-1) protein was found in cell cultures from African donors when compared with that from Caucasians. With regard to keratinocyte growth factor (KGF), the ratio of papillary to reticular fibroblast expression was found to be twofold greater in cell cultures from African donors compared with that from Caucasian donors. The same trend was found regarding MMP-1 and tissue inhibitor metalloproteinase protein 1 (TIMP-1) protein expression. African skin displays a greater convolution of the DEJ and a higher papillary fibroblast activity. These findings reveal that differences between African and Caucasian skin do not only affect upper epidermis but also dermal functions and dermal–epidermal cellular interactions.     

Differences in sun exposure habits between self-reported skin type and ultraviolet sensitivity measured by phototest

Background: Traditionally, classification of skin reactivity to ultraviolet (UV) light is based on self‐estimation of tendency to burn and tan (Fitzpatrick's classification). Although widely accepted, the model has shown to correlate poorly with actual UV sensitivity, measured by phototest. The aim of the present study was to investigate how self‐estimated skin type, according to Fitzpatrick, and actual UV sensitivity measured by phototest correlate with sun exposure and protection. Methods: One hundred and sixty‐six voluntary patients visiting their general practitioner for investigation of suspicious skin tumours were recruited for the study, and filled out a questionnaire, mapping sun habits and sun protection behaviour, based on five‐point Likert responses. The patients reported their skin type (I–VI) according to Fitzpatrick, and a phototest was performed to determine the minimal erythema dose. Results: For most of the questions, high self‐estimated UV sensitivity, according to Fitzpatrick, appeared to be associated with a higher level of sun avoidance/protection (P<0.05). For actual UV sensitivity, however, the difference in response distribution was only significant for sunscreen use, and did not show a similar apparent association related to the degree of UV sensitivity. Conclusion: Self‐estimated skin UV sensitivity, according to Fitzpatrick's classification, appears to be a stronger predictor of sun exposure and protection than actual UV sensitivity measured by phototest.     

Epidermal thickness at different body sites: relationship to age, gender, pigmentation, blood content, skin type and smoking habits

Epidermal thickness and its relationship to age, gender, skin type, pigmentation, blood content, smoking habits and body site is important in dermatologic research and was investigated in this study. Biopsies from three different body sites of 71 human volunteers were obtained, and thickness of the stratum corneum and cellular epidermis was measured microscopically using a preparation technique preventing tissue damage. Multiple regressions analysis was used to evaluate the effect of the various factors independently of each other. Mean (SD) thickness of the stratum corneum was 18.3 (4.9) microm at the dorsal aspect of the forearm, 11.0 (2.2) microm at the shoulder and 14.9 (3.4) microm at the buttock. Corresponding values for the cellular epidermis were 56.6 (11.5) microm, 70.3 (13.6) microm and 81.5 (15.7) microm, respectively. Body site largely explains the variation in epidermal thickness, but also a significant individual variation was observed. Thickness of the stratum corneum correlated positively to pigmentation (p = 0.0008) and negatively to the number of years of smoking (p < 0.0001). Thickness of the cellular epidermis correlated positively to blood content (P = 0.028) and was greater in males than in females (P < 0.0001). Epidermal thickness was not correlated to age or skin type.     

Morphometry of human epidermis in vivo by real-time confocal microscopy

Real-time confocal microscopy has brought substantial improvements to the imaging of the human skin in vivo. On early images, the stratum corneum could be distinguished from the living epidermis and the circulatory network of the superficial dermis. We have adapted the Tandem Scanning Microscope to obtain images of the living skin, showing thinner structures such as the stratum lucidum and the dermo-epidermal junction, both of which are essential markers for micron-order measurements of the thickness of the stratum corneum and living epidermis. The measurements were corrected for the differences in the refractive index of the various cutaneous layers, and the undulation of the dermo-epidermal junction. Furthermore, nucleus size and number could be assessed from horizontal optical sections. To illustrate the sensitivity of the thickness measurements, changes in the thickness of the epidermis were recorded during and after stripping of the horny layers. This non-invasive methodology is a very promising tool for morphometric studies of the living human skin at the cellular level.     

In vivo quantification of epidermis pigmentation and dermis papilla density with reflectance confocal microscopy: variations with age and skin phototype

Reflectance confocal microscopy (RCM) may help to quantify variations of skin pigmentation induced by different stimuli such as UV radiation or therapeutic intervention. The objective of our work was to identify RCM parameters able to quantify in vivo dermis papilla density and epidermis pigmentation potentially applicable in clinical studies. The study included 111 healthy female volunteers with phototypes I-VI. Photo-exposed and photo-protected anatomical sites were imaged. The effect of age was also assessed. Four epidermis components were specifically investigated: stratum corneum, stratum spinosum, basal epidermal layer and dermo-epidermal junction. Laser power, diameter of corneocytes and upper spinous keratinocytes, brightness of upper spinous and interpapillary spinous keratinocytes, number of dermal papillae and papillary contrast were systematically assessed. Papillary contrast measured at the dermo-epidermal junction appeared to be a reliable marker of epidermis pigmentation and showed a strong correlation with skin pigmentation assessed clinically using the Fitzpatrick's classification. Brightness of upper spinous and interpapillary spinous keratinocytes was not influenced by the skin phototype. The number of dermal papillae was significantly lower in subjects with phototypes I-II as compared with darker skin subjects. A dramatic reduction in the number of dermal papillae was noticed with age, particularly in subjects with fair skin. The method presented here provides a new in vivo investigation tool for quantification of dermis papilla density and epidermal pigmentation. Papillary contrast measured at the dermo-epidermal junction may be selected as a marker of skin pigmentation for evaluation in clinical studies.     

Epidermal thickness measured by light microscopy: a methodological study

Background/aims: Epidermal thickness is frequently measured by light microscopy. The preservation and staining methods may alter the proportions of the specimens and thereby influence the measurements. The aim of the present study was to describe: 1) a standardized light microscopic method to quantify the thicknesses of the stratum corneum and the cellular epidermal layers, 2) the variations according to preparation and staining techniques, and 3) the observer variability. Methods : One hundred and sixty skin biopsies from 67 human volunteers were included. The cellular epidermis and the stratum corneum were estimated in sections preserved by freezing and subsequent preparation with cryostat or formalin-paraffin techniques. The slides were stained with haematoxylin-eosin or er-ythrocin, and thicknesses of the stratum corneum and the cellular epidermis were measured by a calibrated ruler and an ocular grid, respectively. Results: The formalin fixation gave slightly higher values for the cellular epidermis than the cryostat technique. In comparison to erythrocin staining, haematoxylin-eosin gave a significantly thinner stratum corneum. No significant inter- or intra-observer variation was found for the thickness of the stratum corneum assessed twice by two experienced observers. However, the two observers differed slightly from each other on the thickness of the cellular epidermis. Conclusion: It is found that thickness measurements of the stratum corneum and the cellular epidermis are reliably performed on cryostatic cut sections stained with haematoxylin-eosin.     

Ability to estimate relative percutaneous penetration via a surrogate maker – trans epidermal water loss?

Aims: This study measures the dynamic change of the trans‐epidermal water loss (TEWL) rate and in vitro skin permeation data of tritiated water and [¹⁴C]‐clonidine HCl in order to refine our knowledge in the relationship between percutaneous penetration and TEWL. Measures: TEWL values were measured before and during the experimental period. Single application of tritiated water and [¹⁴C]‐clonidine HCl were dosed at the same time on dermatomed human skin samples collected from 12 donors in a flow through diffusion cell system. Radioactivity of absorbed dose: stratum corneum, epidermis, dermis, receptor fluid collected every 4 hours, as well as removable dose residue was counted to determine accountability, percent dose, μg equivalent, and flux rate. These data were further combined with TEWL values to analyze their possible relationship. Results: Results showed that baseline TEWL values correlated with the thickness of dermatomed skin (r=?0.44, P=0.007), and with tritiated water fluxes (r=0.34, P=0.04) and [¹⁴C]‐clonidine HCl (r=0.36; P=0.03). The fluxes of tritiated water and [¹⁴C]‐clonidine HCl were correlated (r=0.67, P<0.001). When TEWL and permeation data were compared, the pattern of tritiated water expressed as a percent dose permeated in receptor fluid resembled the TEWL pattern. Conclusion: The methodology described provides evidences of the correlation of TEWL and skin integrity and skin permeation and further demonstrates to be a rapid alternative to tritiated water permeation for measuring skin barrier functions in vitro. To develop TEWL measurement as a possible predictive model to assess in vitro percutaneous absorption, however more chemicals with various physical‐chemical properties need to be examined, and the relationships to TEWL and tritiated water flux better defined.     

Silencing of homeobox A5 gene in the stratum corneum of psoriasis

Analysis of psoriatic parakeratotic cells is helpful for understanding the pathogenesis of psoriasis. Methylation analysis can be performed on psoriatic scales, but it is unclear whether genes can be silenced by DNA methylation in psoriatic stratum corneum. The present study was conducted to detect genes silenced in psoriatic stratum corneum. Methylation array analysis with 485 577 probes, quantitative real‐time methylation‐specific PCR (RT‐MSP) and bisulphite sequencing were performed for 30 psoriatic scale samples, 6 fully developed psoriatic skin samples and 12 normal skin samples. Immunohistochemical staining of HOXA5 was performed for 29 psoriatic epidermal samples and 13 normal epidermal samples. The genome‐wide methylation array detected two CpG sites within CpG islands (CGIs) located in promoter regions of HOXA5 and LIAS that had methylation levels of >0.6 in at least one of the three psoriatic scale samples and of <0.2 in all three normal skin tissue samples (methylation rate range, 0.0‐1.0). RT‐MSP for HOXA5CGI, in which the primers were successfully developed, revealed that the average methylation level of 27 psoriasis scales (60.2%) is significantly higher than that of 9 normal skin samples (34.6%) (P=.013). Immunohistochemical staining revealed that HOXA5 protein was not expressed in the stratum corneum of fully developed psoriatic epidermis, but the protein was expressed in the stratum corneum of incompletely developed epidermis and normal epidermis. In conclusion, HOXA5 can be silenced in the stratum corneum of psoriasis. The silenced gene was identified by non‐invasive methylation analysis of psoriatic scales.     

The growth of ichthyotic epidermal cells in a 3-dimensional reconstruction of human skin, the skin equivalent

We have studied the differentiation of ichthyotic epidermis in vitro using the skin equivalent model. The morphology of these ichthyotic cultures has been investigated using histopathological and histometric techniques including epidermal and stratum corneum thickness measurements. The skin equivalents have also been investigated for the presence of markers of differentiation using immunolocalization techniques. These markers include the 65·5 and 67 kDa keratins, desmoplakin, involuerin, laminin and filaggrin. It has been shown that the ichthyotic epidermis develops a fully differentiated epidermis and stratum corneum, equivalent to those seen in normal skin equivalents.     

Skin temperature of UV-induced erythema correlated to laser Doppler flowmetry and skin reflectance measured redness

Background/aims: The sensitivity of human skin to UV radiation is investigated by visual grading of the resulting erythema reactions 24 h after exposure to a series of increasing UV doses. Visual erythema assessment is, however, subjective and depends on pigmentation and redness of the adjacent un-irradiated skin and can be aided by skin reflectance spectroscopy and laser Doppler blood flow measurements. Erythema is accompanied by a raised skin temperature, and this reaction might be utilised as a simple objective measurement of UV sensitivity. Methods: Sixteen patients with cutaneous malignant melanoma, 16 patients with basal cell carcinoma, and 36 healthy people were phototested with simulated sunlight on previously UV un-exposed buttock skin. The resulting erythema reactions were graded visually 20-24 h post-exposure and measured by skin reflectance spectroscopy and laser Doppler flowmetry, and the surface skin temperature was determined in the erythema reactions and in adjacent un-irradiated skin by a contact thermometer. Results: Skin surface temperature in UV-induced erythema reactions was dose dependent, was statistically identical in skin cancer patients and in healthy people, and was age independent. The average temperature increase in barely perceptible erythema was 0.7°C (SD=1.1°C), and in bright red erythema it was 3.5°C (SD=2.0°C). Skin surface temperature increases were correlated to measurements by skin reflectance spectroscopy and by laser Doppler flowmetry. Conclusions: Skin surface temperature changes can be used as a simple objective measurement of UV sensitivity in healthy people and in skin cancer patients and may be particularly useful in heavily pigmented people where visual assessment of erythema is difficult or impossible.     

Do we alter ultraviolet sensitivity in vivo with stratum corneum rehydration? A pilot study and review of the literature

BACKGROUND: Numerous therapeutic schemes recommend topical administration of emollients immediately prior to ultraviolet (UV) B therapy. The rationale behind the clinical improvement is a presumed enhancement of UV transmission through the epidermis. Originating from this clinical observation, there has been some concern as to whether a well-hydrated skin in general might be more susceptible to actinic damage. OBJECTIVES: To investigate whether rehydration of healthy skin causes an altered UVB sensitivity in vivo. METHODS: We determined minimal erythema doses (MEDs) and erythema sum scores (ESSs) after differential rehydration of the skin in 10 healthy volunteers. In each subject six UVB phototests were performed after pretreatment with five different emulsifying ointments (unguentum emulsificans and dilutions with 30, 50, 70 and 90% aqua purificans) plus a negative control. In vivo evaluation of stratum corneum hydration was performed by measurement of electrical capacitance. RESULTS: The results of this randomized, double-blind in vivo study indicated that rehydration of normal stratum corneum with the emulsifying ointments tested did not result in a significantly altered sensitivity to the erythematous effects of UVB irradiation (no significant differences in MED and ESS). Furthermore, there was no correlation between measured stratum corneum hydration and the erythema response of healthy skin. CONCLUSIONS: Although many schemes recommend the administration of emollients prior to UV therapy, there have also been calls for caution, as an uncritical application may interfere with such treatment. We showed that the emulsifying ointments tested exhibited no photoprotective potential and thus are suitable for the pretreatment of psoriasis prior to phototherapy. It has long been discussed whether the effects of emollient pretreatment on response to UV occur only in psoriatic skin or also in healthy skin. Our results indicated that stratum corneum rehydration did not result in a significantly increased erythema response of healthy skin to UVB exposure. With regard to the use of rehydrating cosmetics in everyday life, the outcome of our pilot study is reassuring, as we could not confirm with our experimental design that well-hydrated healthy skin is more prone to actinic damage.     

Minimal erythema dose and minimal melanogenesis dose relate better to objectively measured skin type than to Fitzpatricks skin type

Background: Fitzpatrick skin type (FST I–IV) is a subjective expression of ultraviolet (UV) sensitivity based on erythema and tanning reactivity after a single exposure. Pigment protection factor (PPF) is an objective measurement of skin sensitivity in all skin types after a single exposure. Methods: The aim was to compare FST and PPF with clinically determined minimal erythema dose (MED) and minimal melanogenesis dose (MMD) in 84 persons with skin types I–V both after single and multiple exposures (one, four, five, six, or 12) to buttock and back skin. Results: FST was better correlated to MED than to MMD, and FST correlated better to constitutive than to facultative pigmented areas after multiple exposures rather than to a single exposure. PPF was generally much better correlated to MED and MMD than FST especially after a single exposure and multiple exposures with steady‐state pigmentation. Multiple regression analyses showed that MED was the only significant, or most important determinator, of both FST and PPF. The correlation coefficient was highly significant for PPF (r²=82). Conclusions: PPF is a better predictor of the individual UV sensitivity (linear relation) than FST (only 4 grades) and PPF can substitute FST.     

In vivo quantitative analysis of the effect of hydration (immersion and Vaseline treatment) in skin layers using high‐resolution MRI and magnetisation transfer contrast*

Background/aims: Many claims are made as to the efficacy of topical preparations in moisturising the skin, yet most of these claims cannot be substantiated by scientific study for the skin layers beneath the stratum corneum, and yield no information on the remainder of the epidermis and dermis. This argues for an in vivo quantitative method for measuring the effect of water loading extended to various layers of the skin. Methods: Detailed high‐resolution in vivo MRI studies of hydration and dehydration of finger pad skin layers were conducted on one normal subject using two moisturisation methods (topical white soft paraffin (Vaseline) and water immersion). The dehydration study was carried out immediately following removal from prolonged skin moisturisation. Inter‐individual variability for skin hydration (group study) was studied in seven healthy volunteers at 0 and 7 h hydration with Vaseline. Location dependence in skin hydration was investigated on the same subject by looking into the hydration of forearm and finger pad skin. System stability and measurement reproducibility was verified through a detailed phantom study. Results: Images of normal and hydrated human skin were obtained in vivo at voxel dimensions of 50 μm×150 μm×1000 μm. The effect of hydration and dehydration as a function of exposure to moisturiser (i.e. water and Vaseline) on the image signal intensity, observed T1, and interaction of free and bound water in specific tissues were identified and correlated with existing physiological knowledge. Swelling of stratum corneum due to hydration was expressed as an in vivo model of tissue hydration. Conclusion: Results of the dehydration study showed that the changes due to the previous hydration of the skin are reversible for all skin layers. For both moisturisation methods (i.e. Vaseline and skin bathing), the effects of hydration and dehydration on the skin were similar. The trends of the MRI parameters for finger pad and arm skin were similar. The group study showed low inter‐subject variability of hydration on stratum corneum and epidermis.     

Photoprotection by melanin—a comparison of black and Caucasian skin

The photoprotective role of melanin was evaluated by comparing the transmission of ultraviolet (UV) radiation through skin samples of blacks and Caucasians, using both biologic and spectroscopic techniques. UVA transmission was measured using fluoranthene, which causes a phototoxic response to UVA wavelength. UVB was measured by monitoring erythema produced by either a 150-watt xenon arc or FS-20 sunlamps. It was found that on the average, five times as much ultraviolet light (UVB and UVA) reaches the upper dermis of Caucasians as reaches that of blacks. Differences in transmission between the stratum corneum of blacks and of Caucasians were far less striking. The main site of UV filtration in Caucasians is the stratum corneum, whereas in blacks it is the malpighian layers. Melanin acts as a neutral density filter, reducing all wavelengths of light equally. The superior photoprotection of black epidermis is due not only to increased melanin content but also to other factors related to packaging and distribution of melanosomes. Not only are these data consistent with epidemiologic evidence, but they also may indicate why blacks are less disposed to phototoxic drug responses as well as less susceptible to acute and chronic actinic damage.     

Urocanic acid isomers and photosensitivity in healthy children

Episodes of intense sun exposure, particularly in childhood, seem to carry a risk for the development of malignant melanoma in later life. However, little is known about photosensitivity and natural photoprotection in children. In adult subjects, photoprotection is provided mainly by the epidermal content of melanin and the thickness of the stratum corneum, while the amount of urocanic acid (UCA), a major ultraviolet-absorbing component of the stratum corneum, is not thought to contribute significantly to photoprotection. The minimal erythema dose (MED) was determined in 22 healthy children aged 6–13 years and in 36 healthy adults (mean age 28.1 years). Pigmentation was measured at six body sites by use of reflectance spectroscopy and the concentration of UCA isomers was measured in a sun-exposed area (upper back) and in unexposed buttock skin. No significant differences between children and adults were found, either in pigmentation at exposed and unexposed body sites, or in MED. The concentration of total UCA was significantly higher in the children than in the adults on the buttock (median 22.2 vs. 13.6 nmol/cm²), but not on the back. On exposed back skin, the children had a significantly higher percentage of cis -UCA than the adults (median 60.1 vs. 28.3%), while no difference was found on the buttock. In both groups, a significant correlation was found between pigmentation and MED (children: Spearman correlation coefficient 0.58, P  = 0.006; adults: Spearman correlation coefficient 0.69, P  < 0.0001), indicating that pigmentation is of major importance in determining photosensitivity in children as well as in adults. The concentration of total UCA did not correlate with the MED in either group.     

Water content and thickness of the stratum corneum contribute to skin surface morphology

Abstract Skin surface morphology has long been recognized as reflecting skin pathology. In the present study, we evaluated skin surface morphology using hairless mice under contrasting conditions of humidity. The skin surface microrelief was recorded with opaque quick-drying silicone rubber, and examined under a microscope. A binary image was produced by density slicing. Within 3 days of exposure to dry conditions, skin roughness was significantly increased. The skin roughness was partially mitigated by topical application of an aqueous solution of glycerol or hydration by immersion in water. A significant correlation between skin roughness and stratum corneum thickness was also observed. These results suggest that skin surface morphology is associated with both water content and thickness of the stratum corneum. Received: 29 November 1999 / Received: 1 March 2000 / Accepted: 22 March 2000     

Effect of exposure of human skin to a dry environment

Background/aims: Changes in the skin conditions after exposure to low humidity have been generally experienced in everyday life, but there have been few reports to approach it—especially in healthy skin. We have examined the effect of low humidity on healthy human skin by using noninvasive measurement devices. Methods: Skin conditions on the ventral forearm and the cheek before and after 3 or 6 h exposure to low humidity were evaluated by measuring skin surface conductance, skin surface capacitance and transepidermal water loss. Skin surface replicas were also taken before and after exposure and analysed for roughness parameters—Ra (arithmetic mean roughness value), Rz (10-point height), Sm (mean value of the profile element) and VC1 (anisotropy of skin furrows). Results: There was a significant decrease of water content of stratum corneum at both test sites from the time points 0 h to 3 h and 6 h (P < 0.01) and transepidermal water loss from the time point 0 h to 6 h (P < 0.05). Regarding the roughness parameters, a significant increase of Rz in the directions of 45°/225° and 90°/270° to the body axis and Sm in the directions of 0°/180° (P < 0.05) on the forearm and VC1 (P < 0.05) on the cheek. The parameter Rz also showed a tendency to increase in the directions of 45°/225° (P = 0.06) on the cheek. A specific pattern of the changes to be related to the Langer's lines in the surface morphology was observed. The changes of skin surface pattern in our experiment lead us to consider that exposure to low humidity even in such a short period would be related to inducing aggravation of skin texture and the formation of fine wrinkles. Conclusion: A short exposure of skin to a low-humidity environment induced changes in the moisture contents in the stratum corneum and skin surface pattern, which lead us to assume that a dry environment in our daily life would make fine wrinkles related to lack of water in the stratum corneum.