A study of diurnal variation in wrinkles on the human face

We recently evaluated diurnal variations in facial skin elasticity and thickness and reported a decrease in skin thickness and an increase in skin elasticity in the afternoon compared with the morning. This phenomenon may be associated with the effect of gravity on dermal fluids. There have been no reports on the diurnal variation in wrinkles on the face, and we now describe such a study. The subjects of this study included 38 healthy Japanese males and females (mean age 34 years). Wrinkles on their foreheads, in the corners of their eyes and in their nasolabial grooves were evaluated. Replicas were obtained and skin thickness and skin elasticity measured in the morning (0830–1000 hours) and in the afternoon (1530–1700 hours) of the same day. Image analysis of the replicas showed significant aggravation of wrinkles in all areas of the face in the afternoon compared with the morning. The results of skin thickness and skin elasticity were in agreement with those of our last study. Swelling tended to occur in the morning due to the effects of gravity during sleep. Therefore, wrinkles may be swollen in the morning. Furthermore, repeated movements of the face due to changes of facial expression may gradually increase wrinkle formation and depth from the morning to the afternoon.     

Age-related diurnal changes of dermal oedema: evaluation by high-frequency ultrasound

Using high-frequency ultrasound, we measured the influence of gravitational stress on skin echogenicity in 22 young (age range 17–27; median 19) and 22 elderly (age range 75–100; median 87) healthy adults. B-mode ultrasound images were obtained from the medial malleolus, lateral calf, anterior thigh, volar forearm and the medial aspect of the arm three times daily; in the morning, immediately before rising, and 2 and 12 h later. The echogenicity was measured by counting the number of low echogenic pixels in the image. Pronounced changes of low echogenic pixel numbers were seen in the areas exposed to high gravitational stress, i.e, the ankle and calf. In the young age-group echogenicity of the skin increased steadily during the day, whereas in the elderly population echogenicity decreased 2 h after getting up in the morning, and subsequently returned to the baseline level. In a control group of 10 people (aged 17–83; median 18), who remained in the supine position throughout the day, the echogenicity of the skin remained unchanged. As the echogenicity of the dermis is inversely related to the amount of fluid it contains, our results indicate that young skin responds to gravitational stress by fluid depletion. In the skin of the elderly, the mechanism of fluid removal appears to be defective. The impaired protection against the development of intradermal oedema in the elderly may predispose to the development of lipodermatosclerosis and leg ulceration.     

Effect of dermal thickness, tissue composition, and body site on skin biomechanical properties

BACKGROUND/PURPOSE: Quantitative measurement of skin biomechanical properties has been used effectively in the investigation of physiological changes in tissue structure and function and to determine treatment efficacy. As the methods are applied to new questions, tissue characteristics that may influence the resultant biomechanical properties are important considerations in the research design. For certain applications, variables such as dermal thickness and subdermal tissue composition, as well as age and/or solar exposure, may influence the skin biomechanics. METHODS: We determined the influence of dermal thickness, tissue composition, and age on the skin biomechanical properties at the shoulder, thigh, and calf among 30 healthy females. We compared two devices, the Biomechanical Tissue Characterization System and the Cutometer SEM 575 Skin Elasticity Meter , to determine the effect of tissue sampling size. Dermal thickness was measured with 20 MHz ultrasound (Dermascan C) and tissue composition was inferred from anthropomorphic data. RESULTS: Skin thickness was significantly correlated with stiffness, energy absorption, and U(r)/U(f) for the shoulder. Body mass index (BMI) was significantly correlated with stiffness (negative correlation), energy absorption (positive), and skin thickness (negative) for the shoulder. Significant differences across body sites were observed. The calf was significantly different from the thigh and shoulders for all parameters (P<0.05, one-way anova). The calf had significantly lower laxity, laxity%, elastic deformation, energy absorption, elasticity, elasticity %, U(r), U(f), and U(r)/U(f) and significantly higher stiffness compared with the thighs and shoulders. sites. The thigh and shoulder sites were significantly different for all parameters except U(r)/U(f), elasticity %, laxity%, and stiffness. The dominant and non-dominant sides were significantly different. The dominant side (right for 90% of the subjects) had increased stiffness and decreased energy absorption (tissue softness, compliance) compared with the left side. A significant (P< or =0.02) negative relationship with age was seen for all biomechanical measures except stiffness at the shoulder. For the thigh and calf sites, significant negative correlations with age were found for elasticity %, U(r), and U(r)/U(f). Age and skin thickness were not correlated in this population. Skin thickness and age influenced the energy absorption at the shoulder site. The biological elasticity at the calf site could be predicted by age and BMI. The biological activity at the thigh site could be predicted by skin thickness and BMI. CONCLUSIONS: Significant regional variations in biomechanical properties and dominant side effects were observed. The biomechanical properties were significantly influenced by age. Certain properties varied with dermal thickness and tissue composition. The parameters were well correlated between the two instruments. The Cutometer, with its smaller aperture, was found to be more sensitive to age relationships.     

Skin color of Koreans: statistical evaluation of affecting factors

BACKGROUND: The L*a*b* three-dimensional coordinate system is the most popular system used to measure skin color. The purpose of this study was to collect standard quantified data on Korean skin color using a chromameter CR-300, and to investigate the relationships among skin color and the general and individual factors that affect it. METHODS: The 600 subjects used in this study were selected using a three-stage proportionate stratified and quota sampling method. We examined the color of 12 body parts of each subject and calculated the E* value (total color difference between two objects). This study also analyzed factors that may affect skin color. RESULTS: The average L*a*b* values for the 12 body parts were 61.7462, 9.5618 and 17.0778, respectively. The site of lightest skin was the medial arm (L=63.9249), whereas the darkest was on the forehead (L=58.0044). Redness was highest on the cheek (a=11.8694) and lowest on the medial arm (a=8.1844). Skin color was lighter and more yellow in females than in males, whereas redness was higher in males. In the case of total color difference between two specific sites, the medial upper arm and forearm were the most similar (E=3.23), and the forehead and medial upper arm were the most different in color (E=7.99). CONCLUSION: The factors that significantly (P<0.01) influenced L* were sex, work place and sunbathing, factors that influenced a* were sex, work place and smoking; and the factors that influenced b* were sunbathing and age.     

Variations of hair follicle size and distribution in different body sites

For the evaluation and quantification of follicular penetration processes, the knowledge of variations of hair follicle parameters in different body sites is basic. Characteristics of follicle sizes and potential follicular reservoir were determined in cyanoacrylate skin surface biopsies, taken from seven different skin areas (lateral forehead, back, thorax, upper arm, forearm, thigh, and calf region). The highest hair follicle density and percentage of follicular orifices on the skin surface and infundibular surface were found on the forehead, whereas the highest average size of the follicular orifices was measured in the calf region. The highest infundibular volume and therefore a potential follicular reservoir was calculated for the forehead and for the calf region, although the calf region showed the lowest hair follicle density. The calculated follicular volume of these two skin areas was as high as the estimated reservoir of the stratum corneum. The lowest values for every other parameter were found on the forearm. The present investigation clearly contradicts former hypothesis that the amount of appendages of the total skin surface represents not more than 0.1%. Every body region disposes its own hair follicle characteristics, which, in the future, should lead us to a differential evaluation of skin penetration processes and a completely different understanding of penetration of topically applied drugs and cosmetics.     

Smoking and skin: a study of the physical qualities and histology of skin in smokers and non-smokers

Tobacco smoke is toxic to cells and could be a factor contributing to accelerated skin ageing. The aim of this study was to provide new information on the possible effects of smoking on the physical qualities of skin and the morphology of elastic fibres. The study population consisted of 98 men, including 47 current smokers and 51 never-smokers. Skin thickness and elasticity were measured from cheek, temple, abdomen, dorsal forearm and non-sun-exposed upper inner arm. Verhoeff-stained punch biopsies from the non-sun-exposed upper inner arm were assessed with a computerized image analyser in a blinded fashion to assess the amount and width of elastic fibres. The thickness of cheek skin was increased in the smokers, but skin thickness in other measured sites did not differ between the groups. The amount and width of elastic fibres in the sun-protected skin of the smokers and non-smokers did not differ significantly, nor did skin elasticity in this or any other region under evaluation, suggesting that smoking alone affects neither the amount and width of dermal elastic fibres nor the elasticity of skin in male smokers.     

Variations in facial skin thickness and echogenicity with site and age.

The characteristic pattern of reflectivity of facial skin, as evaluated by ultrasound, has not previously been described quantitatively. The aim of this study was to evaluate site- and age-dependent variations in skin thickness and echogenicity of facial skin. A total of 40 women, in different age groups, were studied at 12 different facial skin sites. Echographic images were recorded with a 20 MHz B-Scanner and processed by dedicated software. Skin thickness measurements showed significantly higher values on the lower part of the face, whereas skin echogenicity was higher on the upper part of the face. In elderly subjects, an increase in facial skin thickness and overall echogenicity was observed compared with the younger subjects at all assessed skin areas, except the infraorbital regions. Moreover, modifications of skin echogenicity according to age, consisting in the appearance of a subepidermal band and an enhancement of the lower dermis' reflectivity, were observable at most facial skin sites.     

Influence of age and regional differences on skin elasticity as measured by the Cutometer®

Background/aim: Aging of skin is accompanied by decrease of skin elasticity. Using the noninvasive suction device Cutometer^®, we evaluated the age and regional body differences of the viscoelastic properties of human skin. The objectives of this study were to evaluate the correlation between age and the biomechanical parameters and the regional skin variations.
Methods: A total of 96 healthy women aged 20–75 years were included in this study. The biomechanical properties of the skin were measured by using the Cutometer^®. Measurements were made on the face, upper arm and back.
Results: The age of subjects showed significant positive correlation with R4 and R6, and negative correlation with R2, R5 and R7. The face showed bigger changes of elastic properties than the arm and the back. Especially, the R7 of face was most significantly decreased with aging. We could estimate the so-called 'skin age' by using a correlation equation for this parameter.
Conclusion: The viscoelastic properties were significantly influenced by aging. Also, significant regional variations in the viscoelastic properties were observed. Skin elasticity measurement is useful for the quantitative evaluation of age-related changes.     

Age-related changes in the elastic properties and thickness of human facial skin

Using recently designed, commercially available, non-invasive instruments, we measured the thickness and elasticity of the skin of the face and ventral forearm in 170 women, and evaluated the effects of age and exposure to sunlight. Skin thickness decreased with age in ventral forearm skin, which has limited exposure to sunlight, but increased significantly in the skin of the forehead, corners of the eyes, and cheeks, which are markedly exposed to sunlight. Skin elasticity (U_r/U_f) decreased with age on both the face and forearm. The ratio of viscosity element to elasticity element (U_v/U_e) increased with age at all sites. However, delayed distension (U_v), immediate retraction (U_r), final distension (U_f), and immediate distention (U_e), as individual elements, decreased on the face and increased on the forearm with age. This tendency was more marked after correction for skin thickness. These results suggested the specificity of skin thickness and elasticity in the facial skin. Analysis using a four-element model showed no changes in the elasticity coefficient of Maxwell element on the forearm, but an increase on the face. This indicates quantitative or qualitative changes in elastic fibres in facial skin. Thus, sunlight appears to have a considerable effect on the thickness and physical properties of facial skin.     

Effects of ageing on dermal echogenicity

Background/aims: Changes in the dermis associated with ageing can be detected by high-frequency skin ultrasonography. In photoaged skin, this technique shows a subepidermal low echogenic band (SLEB) that is probably an ultrasound manifestation of elastosis and oedema in the papillary dermis. Since some authors found an association between age and SLEB thickness or its echogenicity on exposed sites, it has been proposed to use these parameters to quantify skin photoageing.
Methods: To determine whether SLEB can be used as a quantitative marker of ageing, its prevalence was determined on forearm skin in a group of 55 individuals (age 18–57 years). The size of SLEB has been measured by quantifying the number of low echogenic pixels in the subepidermal area, which is an accurate method for assessing SLEB severity.
Results: The prevalence of SLEB increased with age, but SLEB was also present in young subjects. The echogenicity of the subepidermal area did not show any age dependence. However, when a ratio of echogenicity between upper and lower dermis was calculated, a linear dependence on age was found.
Conclusions: This study indicates that skin echogenicity measured as a ratio between the upper and lower dermis may be used to objectively estimate photoageing.     

Age-related alterations of echogenicity in Japanese skin

BACKGROUND: Ultrasonic methods are commonly used for the noninvasive measurement of skin thickness. The effects of ageing on the skin have been reported to differ between Asians and Caucasians. Therefore, it is possible that the echogenicity of the skin on ultrasonographic images reflects differences in the skin architecture and properties that may vary among races and environments. OBJECTIVE AND METHODS: Since there have been a few reports on ageing-related changes in ultrasonic echogenicity in Caucasian skin, but not in Asian skin, we evaluated age-related changes in the echogenicity of ultrasonographic images by the ultrasonic B mode at 3 sites on the face (forehead, eye corners, cheeks) considered as sun-exposed areas and on the ventral forearms considered as weakly sun-exposed areas in 130 Japanese females aged from 18 to 83 years. The dermis was divided into 3 layers (upper, middle, lower), and echogenicity was evaluated in each area. RESULTS: No age-related change in echogenicity was observed in the entire dermis. When the dermis was divided into 3 layers (upper, middle and lower dermis), the echogenicity was decreased in the upper layer and increased in the lower layer with age in all skin areas tested. In contrast, there were no age-related changes of echogenicity in the middle dermis. CONCLUSION: These findings suggest that, as for Caucasians, echogenicity in the upper and lower dermis is a useful tool for evaluating skin ageing in the Japanese.     

Distribution density of intraepidermal nerve fibers in normal human skin

A total of 74 specimens was obtained from the normal human skin of patients from 3 to 90 years old. The specimens were roughly classified into 5 groups: 15 for the face group from the face; 15 for the abdomen group from the abdomen; 13 for the back group from the back; 14 for the arm group from the upper arm and forearm; and 17 for the leg group from the thigh and lower leg. They were all fixed in 4% paraformaldehyde and 14% saturated picric acid. Cryostat sections were examined by the immunoperoxidase method and indirect immunofluorescence (IF). Primary antibodies against neurofilament, neuron-specific enolase, protein gene product 9.5 (PGP 9.5) and S-100 protein were used. The most effective method was found to be the combination of IF with PGP 9.5; it visualized the intraepidermal nerve fibers easily and clearly. Of the 74 specimens, 32 (43%) had intraepidermal PGP 9.5-immunoreactive (or nerve) fibers (IPIF), and 42 (57%) did not have any. With reference to the different skin locations, the maximal rate of specimens having IPIF was 57% in the arm group, and the minimum was 23% in the back group. IPIF positive specimens had approximate surface lengths of 6 mm, in which the existence number of the IPIF was 1 to 75. Their distribution density per 1000 epidermal basal cells was highest at 9.63 in the arm group and lowest at 2.89 in the back group. Their thickness was 2.94 +/- 0.83 microns with no significant differences among the five groups. We concluded that intraepidermal nerve fibers may not be distributed evenly in the hairy portions of normal human skin, but they may be present focally. Physiologically, two-point discrimination of itch may be explained by the distribution mode of intraepidermal nerve fibers.     

Quantitative evaluation of chronological ageing and photoageing in vivo: studies on skin echogenicity and thickness

Skin ageing is divided into chronological ageing and photoageing due to the cumulative effects of solar ultraviolet radiation. It is, however, difficult to measure the degree of photoageing and chronological ageing in humans in vivo . Here, we have evaluated the usefulness of ultrasonography for measurement of chronological ageing and photoageing in vivo . Twenty megahertz ultrasonography was performed in 90 individuals (29 men, 61 women, age 18–94) to describe age-related changes in sun-exposed regions with different levels of sun exposure (dorsal and ventral forearm, forehead, ankle) and non-exposed buttock skin. Skin thickness and skin echogenicity in different layers of the dermis were measured in ultrasound images. Additionally, cutaneous photodamage was scored clinically. Age-related changes were dependent on body site as well as layer of the dermis. A progressive, age-related decrease in echogenicity of the upper dermis was found in sun-exposed regions (dorsal forearm, forehead), but not in moderately exposed regions (ventral forearm, ankle). In the buttock an increase in echogenicity was observed. The echogenicity of the lower dermis increased in all examined sites. Skin thickness increased with age in the forehead and buttock, but decreased in the extremity skin. Our findings show that photoageing causes a decrease in echogenicity in the upper dermis. In contrast, chronological ageing is associated with an increase in echogenicity in the lower dermis. Although both increases and decreases in skin thickness were observed in different anatomical regions, there was no general relationship between skin thickness and age. Dermal echogenicity was deemed valuable for in vivo study of chronological ageing and photoageing.     

Fibrillin-rich microfibrils are reduced in photoaged skin. Distribution at the dermal-epidermal junction

Chronic sun exposure results in photoaged skin with deep coarse wrinkles and loss of elasticity. We have examined the distribution and abundance of fibrillin-rich microfibrils, key structural components of the elastic fiber network, in photoaged and photoprotected skin. Punch biopsies taken from photoaged forearm and from photoprotected hip and upper inner arm of 16 subjects with a clinical range of photoaging were examined for fibrillin-1 and fibrillin-2 expression and microfibril distribution. In situ hybridization revealed decreased fibrillin-1 mRNA but unchanged fibrillin-2 mRNA levels in severely photoaged forearm biopsies relative to photoprotected dermal sites. An immunohistochemical approach demonstrated that microfibrils at the dermal-epidermal junction were significantly reduced in moderate to severely photoaged forearm skin. Confocal microscopy revealed that the papillary dermal microfibrillar network was truncated and depleted in photoaged skin. These studies highlight that the fibrillin-rich microfibrillar network associated with the upper dermis undergoes extensive remodeling following solar irradiation. These changes may contribute to the clinical features of photoaging, such as wrinkle formation and loss of elasticity.     

A reliable,non‐invasive measurement tool for anisotropy in normal skin and scar tissue

Background: Anisotropy of the skin varies depending on different locations and pathological conditions. Currently, no reliable non‐invasive measurement tool is available for tissue anisotropy. The Reviscometer^® is an anisotropy measurement tool that measures the resonance running time (RRT) of a shock wave. This study was initiated to establish the reliability of the Reviscometer^® on normal skin and scars, and to provide basic information on tissue alignment in normal skin and scars. Methods: Fifty volunteers and 50 patients underwent measurements on normal skin and scars, respectively. All measurements were performed by the same two observers. Measurements on normal skin were performed on the forearm, upper arm, and abdomen. Results: The results showed that the intraclass correlation coefficient of the inter‐observer reliability was ≥0.79 on normal skin and ≥0.86 on scars. In normal skin, the highest mean RRT was found on the abdomen (156.4±48.8), followed by the upper arm (123.2±33.6) and the forearm (112.5±24.3). A significantly lower mean RRT was found in scars (52.3±21.9) compared with normal skin (91.6±37.7). Conclusion: Reviscometer^® measurements were reliable for normal skin and scars. In addition, clear differences between scars and normal skin but also within different locations on normal skin were identified. The Reviscometer^® can be considered for the evaluation of the efficacy of different treatments.     

Thickness and echogenicity of the skin in children as assessed by 20-MHz ultrasound

BACKGROUND: Skin anatomy and physiology undergo modifications throughout the whole lifespan. In children the skin appears with structural characteristics, as evaluated by histology, which differ from those of adults, especially in the first years of life. OBJECTIVE: The aim of our study was to evaluate skin thickness and echogenicity at different sites in children by 20-MHz ultrasound. METHODS: Eight skin sites of 42 children and 30 young adults were studied with a 20-MHz B scanner. Skin thickness and mean echogenicity were evaluated. The echographic images were processed and segmented by a dedicated program: the 0-30 amplitude interval, which marks the hypoechogenic parts of the tissue, and the 201-255 range, highlighting the hyperreflecting areas, have been selected. RESULTS AND CONCLUSION: Whereas skin thickness shows a gradual increase from birth to adulthood, maturation of the skin leads to variations in the intensity of its echogenicity, depending on the different skin areas. Whereas on the face and the trunk it appears lower in adults with respect to children, a gradual increase can be observed on the limbs with growing age. The distribution of skin reflectivity also greatly varies in different phases of life.     

Ethnic differences in stratum corneum functions between Chinese and Thai infants residing in Bangkok,Thailand

Background/Objectives

Ethnic and racial differences in infant skin have not been well characterized. The purpose of this study was to establish whether there are ethnic differences and similarities in the stratum corneum (SC) functions of Thai and Chinese infants.

Methods

Healthy infants 6 to 24 months of age (N = 60; 30 Thai, 30 Chinese) who resided in Bangkok, Thailand, were enrolled. Transepidermal water loss (TEWL) and SC hydration (capacitance) on the thigh, buttock, and upper arm were measured. Ceramide content was determined in the SC on the upper arm.

Results

SC hydration was not remarkably different between the two ethnicities at any site measured, but TEWL was significantly higher in Chinese infants than in Thai infants at all sites. Hydration of the SC was not significantly correlated with age in either ethnicity. TEWL had significant but weak correlations with age on the thigh and upper arm in Thai infants. Ceramide content was significantly higher in Chinese SC than in Thai SC. No relationship between ceramide content and TEWL or hydration was observed in either ethnicity.

Conclusion

The significant differences in TEWL and ceramide contents between Chinese and Thai infant skin could prove useful in designing skin care and diapering products that are best suited for each ethnicity.     

The face and neck: regional variation in skin barrier function and reactivity

Background/aims: Although there are many reports of regional variations in skin response to various stimuli, only a few studies have been performed on the face. The forearm is the most often used test site while the face is a frequent and specific target of many topical agents (drugs and cosmetics) and cosmetic procedures. The aim of this study was to compare regional variations of cutaneous sensation and skin barrier function in the cheek, neck and forearm before and after application of different stimuli (physical and/or chemical). Methods: Physiological changes of the skin were measured by non-invasive methods: TEWL (transepidermal water loss) and skin capacitance. Furthermore, clinical scoring and subjective sensations were reported. The anatomical sites evaluated were cheek, neck and volar forearm. Results: Great differences in clinical reactions, subjective sensations and skin barrier function in response to various stimuli have been observed between tested areas (cheek, neck and forearm). We observed a greater “sensitivity”, i.e., more severe clinical reactions and subjective sensations of the cheek and neck areas, in relation to chemical stimuli as compared to the forearm. After a mechanical stimulus, the forearm was the most sensitive site, but just for subjective sensations. Concerning skin barrier function, the cheeks exhibited the highest values of TEWL and the forearms the lowest. Conclusion: In view of the high “sensitivity” of the cheek as compared to the forearm, it will be more cautious to assess the safety of facial cosmetics on the sites of intended use.     

Echographic assessment of age-dependent variations of skin thickness

Background/aims: Skin thickness relative to age is complex and may be influenced both by intrinsic changes, extrinsic changes related to sun exposure and constitution, including sex. Age-related changes may also differ in different anatomical sites. The object was to characterize skin aging relative to these influences.
Methods: A-mode and B-mode high-frequency (20 MHz) ultrasound examination was performed using the Dermascan C. 162 subjects were examined (91 women, 71 men) in the age range 27 to 90 years. 6 anatomical locations (forehead, cheek, volar forearm, dorsal forearm, upper abdomen, buttocks) were studied.
Results: Females have thinner skin than men. Subjects aged more than 70 years have significant thinning of the skin. Age-related thinning is more pronounced in women. Relative skin-thickness decrease is less at sun-exposed areas in comparison with protected areas.
Conclusion: Ultrasund examination allows characterization of skin aging, and the influences of sex and anatomical site with sun-induced changes were differently superimposed on intrinsic changes and constitution.     

Frictional properties of human skin: relation to age, sex and anatomical region, stratum corneum hydration and transepidermal water loss

Differences in the dynamic skin friction coefficients (mu) were investigated with respect to age, sex, and anatomical region. A total of 29 volunteers consisting of seven young females, seven old females, seven young males, and eight old males participated in the study. Measurements were obtained from II anatomical regions, namely, the forehead, upper arm, volar and dorsal forearm, postauricular, palm, abdomen, upper and lower back, thigh, and ankle. The friction data were compared with stratum corneum hydration and transepidermal water loss (TEWL). The dynamic friction coefficient did not vary significantly between age and sex groups but varied considerably among the anatomical regions of the body. The forehead and postauricular had the highest mu (0.34 +/- 0.02) while the abdomen had the lowest (0.12 +/- 0.01); the remaining regions had an average mu value of 0.21 +/- 0.01. Similarly, no sex differences were observed for TEWL and stratum corneum hydration. Capacitance was only significantly lower on the palms of the elderly. Regional differences showed a higher state of hydration on the forehead and postauricular as well as the upper arm, upper and lower back when compared with the volar forearm. TEWL was generally lower in the elderly on all anatomical regions except the postauricular and palm. A significant correlation was established between mu and capacitance for most regions. Between mu and TEWL significant correlation was observed only on the palm and thigh. These findings suggest that frictional properties of skin are dependent on more than water content or non-apparent sweating and the role of sebum secretion is suggested as one possible factor.