Variation of skin properties within human forearms demonstrated by non-invasive detection and multi-way analysis

Background/aim: It is known that the properties of human skin vary locally. The purpose of this study was to investigate the properties of human volar forearms even further using advanced non-invasive techniques and numerical methods.
Methods: The skin properties of human volar forearms were investigated using measurements of trans epidermal water loss and multifrequency electrical impedance. Eight sites on the forearms of 27 healthy volunteers were measured. The sites were oriented as squares, four sites on both left and right forearm, approximately 40–50 mm apart.
Results: Analysis of variance showed significant differences for epidermal water loss ( P  < 0.01) and the skin impedance ( P  < 0.001) between the inner and outer sides of the arms. Additionally, parallel factor analysis of the full skin impedance spectra also showed that there are systematic differences between right and left arm ( P  < 0.01).
Conclusion: It is crucial to design skin studies carefully in order to minimise the effects of the local skin properties of human skin.     

The impact of measures for secondary individual prevention of work-related skin diseases in health care workers: 1-year follow-up study

Background:  Specific instruction courses as a tool for secondary prevention of occupational skin disease (secondary individual prevention, SIP courses) affecting individuals have been introduced in Germany. Little is yet known about the outcome of occupational disease and related behavioural patterns following these courses.
Objectives:  To investigate the outcome of occupational skin disease in health care workers (HCW) 1 year after attendance of a SIP course.
Patients/methods:  Two hundred and fifty-three HCW participated in SIP courses and were contacted by telephone 1 year after attendance. Patients were interviewed about skin lesions, medical treatment, sick leave, change of occupation, skin protection, skin care and skin cleansing, and the impact of skin disease.
Results:  The follow-up rate was 81%. The proportion of participants reporting skin lesions decreased significantly (68% at follow-up compared with 77% at baseline; P  = 0.02). Seventy-two per cent reported that their skin lesions had improved. Nine per cent reported having left their occupation due to their skin disease. Skin care and skin protection had improved, while the frequency of reported hand washing was reduced. Twenty-seven per cent said their quality of life was impaired due to the skin disease, compared with 54% at baseline ( P  < 0.001).
Conclusions:  Outcome parameters, including behavioural parameters, indicate a positive impact of courses for SIP on skin health of HCW 1 year after attendance.     

Electrical impedance scanning: a new approach to skin cancer diagnosis

Background/aims: Skin cancer diagnosis depends, to a great extent, on visual inspection and histopathological examination of excised tissues. The aim of this study is to evaluate the ability of electrical impedance scanning to differentiate between benign and malignant skin lesions.
Methods: A preclinical study was conducted on 40 nude mice injected subcutaneously with a human melanoma strain. Impedance measurements were recorded every week to correlate electrical changes with tumor growth and histological findings. A clinical study was also performed on 178 human suspicious skin lesions before excision. The impedance measurements were correlated to the histopathological results.
Results: Normalized conductivity and capacitance, recorded on growing skin tumors in nude mice, were shown to change relative to lesion size. Necrosis, present in most of the larger lesions, was associated with a decrease in the electrical conductivity. Similar electrical parameters were used to classify human melanoma lesions with 92% sensitivity and 67% specificity. In addition, four out of five BCC lesions were correctly diagnosed. Moreover, dysplastic lesions were diagnosed with 91% sensitivity and 59% specificity. For comparison, physicians diagnosed melanoma lesions with 75% sensitivity and 87% specificity and dysplastic lesions with 46% sensitivity and 80% specificity.
Conclusions: The animal study showed that electrical impedance measurements reflect morphological changes related to the growth of a cancerous skin lesion. These findings are in agreement with a preliminary clinical study. Electrical Impedance Scanning can therefore be considered as an objective and non-invasive tool for differentiation between benign and malignant skin lesions.     

Accuracy of clinical diagnosis of skin lesions

Background  Skin cancer is an increasing problem in fair-skinned populations worldwide. It is important that doctors are able to diagnose skin lesions accurately.
Objectives  To compare the clinical with the histological diagnosis of excised skin lesions from a set of epidemiological data. We analysed diagnostic accuracy stratified by histological subtype and body site and examined the histological nature of misclassified diagnosis.
Methods  All excised and histologically confirmed skin cancers in Townsville/Thuringowa, Australia from December 1996 to October 1999 were recorded. Positive predictive values (PPVs) and sensitivities were calculated for the clinical diagnoses and stratified by histological subtype and body site.
Results  Skin excisions in 8694 patients were examined. PPVs for the clinical diagnoses were: basal cell carcinoma (BCC) 72·7%; squamous cell carcinoma (SCC) 49·4%; cutaneous melanoma (CM) 33·3%. Sensitivities for the clinical diagnosis were: BCC 63·9%; SCC 41·1%; CM 33·8%. For BCC, PPVs and sensitivities were higher for the trunk, the shoulders and the face and lower for the extremities. The reverse pattern was seen for SCCs.
Conclusions  Diagnostic accuracy was highest for BCC, the most prevalent lesion. Most excisions were correctly diagnosed or resulted in the removal of malignant lesions. With nonmelanocytic lesions, doctors tended to misclassify benign lesions as malignant, but were less likely to do the reverse. Although a small number of clinically diagnosed common naevi subsequently proved to be melanoma (6·3%), a higher proportion of all melanomas had been classified as common naevi (20·9%). Accuracy of diagnosis was dependent on body site.     

Machine-learning classification of non-melanoma skin cancers from image features obtained by optical coherence tomography

Background/purpose: A number of publications have suggested that optical coherence tomography (OCT) has the potential for non-invasive diagnosis of skin cancer. Currently, individual diagnostic features do not appear sufficiently discriminatory. The combined use of several features may however be useful.
Methods: OCT is based on infrared light, photonics and fibre optics. The system used has an axial resolution of 10 μm, lateral 20 μm. We investigated the combined use of several OCT features from basal cell carcinomas (BCC) and actinic keratosis (AK). We studied BCC (41) and AK (37) lesions in 34 consecutive patients. The diagnostic accuracy of the combined features was assessed using a machine-learning tool.
Results: OCT images of normal skin typically exhibit a layered structure, not present in the lesions imaged. BCCs showed dark globules corresponding to basaloid islands and AKs showed white dots and streaks corresponding to hyperkeratosis. Differences in OCT morphology were not sufficient to differentiate BCC from AK by the naked eye. Machine-learning analysis suggests that when a multiplicity of features is used, correct classification accuracies of 73% (AK) and 81% (BCC) are achieved.
Conclusion: The data extracted from individual OCT scans included both quantitative and qualitative measures, and at the current level of resolution, these single factors appear insufficient for diagnosis. Our approach suggests that it may be possible to extract diagnostic data from the overall architecture of the OCT images with a reasonable diagnostic accuracy when used in combination.     

Biophysical measurements of human forearm skin in vivo: effects of site, gender, chirality and time

Background/aims: Measurements of transepidermal water loss (TEWL) and skin colour are biophysical techniques commonly used to measure the in vivo skin effects of cosmetics, topical medicaments and chemical irritants. The purpose of this study was to investigate the variability of TEWL and skin colour on human forearm skin as a function of regional variation, gender and preferred chirality over an 8 h period.
Methods: Biophysical measurements of TEWL and skin colour were made at five sites on both forearms of male ( n =8) and female ( n =9) human volunteers in vivo (38% relative humidity, 21°C).
Results: Rates of TEWL at the forearm midpoint were 10% lower than at the forearm extremities ( P <0.01). Skin redness ( a *) near the wrist was 5–10% higher than at other sites ( P <0.05). Rates of TEWL were 5% higher in male volunteers ( P <0.05). Red and blue ( b *) colour measurements of male forearm skin differed by 18% and 20% in comparison with female, respectively. Rates of TEWL, skin brightness ( L *) and b * decreased by 9% ( P <0.05), 1.8% ( P <0.05) and 4% ( P <0.05), respectively, with time whereas a * and skin temperature increased by 4.5% ( P <0.01) and 7.2% ( P <0.01), respectively. There was a significant correlation between the change in all measured parameters with time.
Conclusions: Significant differences in TEWL and skin colour were identified that may have relevance in the design and interpretation of multivariate analyses of human forearm skin. Diurnal variation of TEWL, skin colour and temperature may have a single underlying mechanism.     

Is it possible to characterize objectively sensitive skin?

Background/purpose: Sensitive skin is a subject of intense research work. However, its contours have not been defined and properly investigated so far. The aim of this work was to characterize objectively the consumers of cosmetic products, which referred skin susceptibility to several agents or conditions.
Methods: Twenty-four healthy female volunteers, mean age 38.9±13 years were recruited. The volunteers were fully informed about the study having previously expressed their consent, and were grouped in to I: individuals without any skin sensitivity complaint and II: individuals with self-reported sensitive skin to regular contact with household cleaning products. Sodium lauryl sulphate was used as a 'provocative' agent and it was applied on the back of the volunteers' hands, as an occlusive patch for 24 h. After the patch removal (30 min, 7 and 14 days), the variables erythema, transepidermal water loss, stratum corneum hydration and blood perfusion were measured.
Results: No evidence of a statistical difference was found between the biomechanical behaviour of the skin of the two groups.
Conclusion: The results of our study did not enable us to establish a clear discrimination between sensitive and non-sensitive skin, which once again underlines the subjective nature of this condition.     

Preliminary study among truck drivers in Turkey: effects of ultraviolet light on some skin entities

In this study, we aimed to compare driver (left) and opposite (right) sides for some skin entities in drivers. We also evaluated the effect of occupational duration, age and skin type among this population. One hundred and forty-eight truck drivers were included in this study. Sun exposed areas were classified. Dermatological entities such as actinic keratosis, solar lentigo, seborrheic keratosis, melanocytic nevus, spider angioma, ephelid, basal cell carcinoma (BCC), squamous cell carcinoma, and melanoma were compared to driver and right sides. In addition, drivers were divided into two subgroups according to: (i) age (subgroups A1, 20-40 years, and A2, >40 years); (ii) occupational duration (subgroups O1, 1-10 years, and 02, >10 years); and (iii) skin type (subgroups S1, skin types I and II, and S2, skin types III and IV. Each of the two subgroups were compared with respect to the total prevalence (left and right sides) of lesions excluding the location. Seborrheic keratosis and lentigo solaris were found to be increased on the driver side of the face (P = 0.00) and ear (P = 0.013), respectively. Statistically significant increases of lesions on the driver side were determined according to the subgroups: melanocytic nevi were found to be increased on the driver side in A1 (P = 0.00), A2 (P = 0.00), O2 (P = 0.00), S1 (P = 0.00) and S2 (P = 0.006) groups; actinic keratoses were found to be significantly increased on the driver side in A2 and O2 groups (P = 0.03 for both).     

Atopic dermatitis in adults: evaluation of peripheral blood mononuclear cells proliferation response to Staphylococcus aureus enterotoxins A and B and analysis of interleukin-18 secretion

Background:  Atopic dermatitis (AD) is a chronic, inflammatory skin disease with a high prevalence and complex pathogenesis. The skin of AD patients is usually colonized by Staphylococcus aureus ( S. aureus ); its exotoxins may trigger or enhance the cutaneous inflammation. Several mediators are related to the AD immune imbalance and interleukin-18 (IL-18), an inflammatory cytokine, may play a role in the atopic skin inflammation.
Aims:  To evaluate peripheral blood mononuclear cells (PBMC) proliferation response to staphylococcal enterotoxins A (SEA) and B (SEB) and the levels of IL-18 in adults with AD.
Methods:  Thirty-eight adult patients with AD and 33 healthy controls were analysed. PBMC were stimulated with SEA and SEB, phytohemaglutinin (PHA), pokeweed (PWM), tetanus toxoid (TT) and Candida albicans (CMA). IL-18 secretion from PBMC culture supernatants and sera were measured by ELISA.
Results:  A significant inhibition of the PBMC proliferation response to SEA, PHA, TT and CMA of AD patients was detected ( P  ≤ 0.05). Furthermore, increased levels of IL-18 were detected both in sera and non-stimulated PBMC culture supernatants from AD patients ( P  ≤ 0.05).
Conclusions:  A decreased PBMC proliferation response to distinct antigens and mitogens (TT, CMA, SEA and PHA) in adults with AD suggest a compromised immune profile. IL-18 secretion from AD upon stimulation was similar from controls, which may indicate a diverse mechanism of skin inflammation maintained by Staphylococcus aureus. On the other hand, augmented IL-18 secretion from AD sera and non-stimulated cell culture may enhance the immune dysfunction observed in AD, leading to constant skin inflammation.     

In vivo thickness measurement of basal cell carcinoma and actinic keratosis with optical coherence tomography and 20-MHz ultrasound

Background  Accurate assessment of tumour size is important when planning treatment of nonmelanoma skin cancer (NMSC). Imaging with optical coherence tomography (OCT) has the potential to diagnose and measure depth of NMSC.
Objectives  To compare accuracy of mean tumour thickness measurement in NMSC tumours < 2 mm of depth using OCT and 20-MHz high-frequency ultrasound (HFUS). In addition, OCT morphology of NMSC was studied in OCT images and the influence of histological and colorimetric values on the quality and penetration depth in OCT images was estimated.
Methods  In total, 93 patients were scanned and 34 lesions [23 basal cell carcinoma (BCC) and 11 actinic keratosis (AK) lesions] < 2 mm thick and easily identified in OCT images were studied. OCT and HFUS were compared with biopsies. The influence of skin pigmentation and infiltration analgesia on OCT image quality was studied. Skin colour was measured with a colorimeter.
Results  OCT presented narrower limits of agreement than HFUS. Both methods overestimated thickness but OCT was significantly less biased (0·392 mm vs. 0·713 mm). No relation between OCT penetration depth and skin colour was found.
Conclusions  OCT appears more precise and less biased than HFUS for thickness measurement in AK and BCC lesions < 2 mm, but both OCT and especially HFUS tended to overestimate tumour thickness.     

Real-time spatial compound ultrasound imaging of skin

Purpose:  The aim of our study was to evaluate the potential of real-time spatial compound imaging (RTSCI) in dermatology.
Materials and methods:  An ATL 5000 SonoCT equipped with compact linear 15–7 MHz and linear 12–5 MHz transducers was obtained for skin visualization in a group of dermatological patients with various skin diseases.
Results:  Thirty-four people participated: 21 patients with various skin diseases and 13 persons with normal skin. The mean age was 43.4 years. For many diseases, RTSCI gave useful information about the lesional structure, thickness and relationship with surrounding structures.
Conclusion: RTSCI allows objective, accurate, noninvasive and easy measurements of several parameters of skin morphology. It is useful in clinical trials, for evaluation of the effects of therapy, for preoperative evaluation of dermatological lesions, and enables visualization of subclinical and deep lesions, giving physicians the possibility of starting treatment before disease intensity increases. However, even such highly advanced ultrasound cannot completely substitute the clinical dermatological approach and the occasional need for histological diagnosis. This new method may, however, become an important adjunct method for the study of skin lesions.     

A prospective study of the incidence of skin cancer and its risk factors in a Spanish Mediterranean population of kidney transplant recipients

BACKGROUND: Skin cancer is the most common malignancy occurring in kidney transplant recipients (KTRs). OBJECTIVES: Our purpose was to investigate, prospectively, the cumulative incidence of cancerous and precancerous skin lesions as well as their risk factors in a close follow-up population of KTRs from a Mediterranean area of Spain. PATIENTS AND METHODS: One hundred and seventy-four consecutive KTRs were examined at the moment of transplant and then at 6-month intervals. The cumulative incidence of skin cancer was computed. To analyse the role of potential risk factors (age at transplantation, cause of renal failure, duration of pretransplant dialysis, type of immunosuppressive regimen, sun-reactive skin type and history of occupational sun exposure), the Cox regression method was used. RESULTS: After a median follow-up of 72 months (range, 12-140), 39 patients (25.3%) developed 142 tumours [84 basal cell carcinoma (BCC) and 58 squamous cell carcinoma (SCC)]. The BCC/SCC ratio was 1.4 : 1. The cumulative incidence for skin cancer was 13% after 3 years of graft survival, increasing to 27.5% at 6 years and 48% at 10 years. Only age at the time of transplantation and occupational sun exposure had statistical significance as risk factors (P < 0.001). CONCLUSIONS: Our study confirms the high incidence of non-melanoma skin cancer among KTRs in a Mediterranean population with occupational sun exposure and the patient's age at the time of transplantation being the main risk factors. We believe that all organ transplant programs should provide educational information about protecting oneself from the sun as well as include follow-up visits by dermatologists in order to facilitate early diagnosis and treatment of skin cancer.     

Fluorescence lifetime imaging distinguishes basal cell carcinoma from surrounding uninvolved skin

Background  Fluorescence lifetime imaging (FLIM) is a novel imaging technique that generates image contrast between different states of tissue due to differences in fluorescence decay rates.
Objectives  To establish whether FLIM of skin autofluorescence can provide useful contrast between basal cell carcinomas (BCCs) and surrounding uninvolved skin.
Methods  Unstained excision biopsies of 25 BCCs were imaged en face with FLIM following excitation of autofluorescence with a 355 nm pulsed ultraviolet laser.
Results  Using FLIM we were able to distinguish areas of BCC from surrounding skin in an ex vivo study. Significant reductions in mean fluorescence lifetimes between areas of BCC and areas of surrounding uninvolved skin were demonstrated ( P  <   0·0001). These differences were apparent irrespective of the decay model used to calculate the fluorescence lifetimes (single vs. stretched exponential) or the long-pass filter through which the emitted autofluorescence was collected (375 vs. 455 nm). Conversely, there was no significant difference between the BCC and uninvolved areas of each sample when mean autofluorescence intensities were examined. Moreover, wide-field false-colour images of fluorescence lifetimes clearly discriminated areas of BCC from the surrounding uninvolved skin.
Conclusions  We therefore believe that FLIM has a potential future clinical role in imaging BCCs for rapid and noninvasive tumour delineation and as an aid to determine adequate excision margins with best preservation of normal tissue.     

Effects of blood glucose fluctuation on skin biophysical properties, structure and antioxidant status in an animal model

Background.  Intermittent blood-glucose fluctuation (BGF) can accelerate diabetes and its complications, but it is still unknown whether BGF can damage the skin of patients with diabetes.
Aim.  To investigate the effects of repetitive fluctuation in blood glucose concentration on the biophysical properties, structure and antioxidant capacity of diabetic mouse skin.
Methods.  Mice with alloxan-induced diabetes were injected with glucose three times daily to induce repetitive BGF. Six weeks later, skin elasticity and skin hydration were measured to evaluate skin water-holding capacity and contraction function. The histological changes of skin were also studied, using haematoxylin and eosin. In addition, we compared levels of blood sugar and advanced glycation end products (AGEs), the activities of superoxide dismutase (SOD) and the contents of malondialdehyde (MDA) and hydroxyproline in the skin of normal mice and diabetic mice with or without BGF.
Results.  The diabetic mice with BGF displayed an 18.6% increase in blood sugar level, an 11.3% increase in AGEs content and a 13.1% increase in MDA content compared with the diabetic mice ( P <  0.01). There was a greater reduction in skin elasticity, skin hydration, hydroxyproline content and SOD activity in the diabetic mice with BGF ( P <  0.01). Histological examination showed that BGF enhanced skin lesions in diabetic mice.
Conclusions.  Repetitive fluctuation in blood-glucose concentration produced a marked detrimental effect on skin structure and function in diabetic mice. The deleterious effects of BGF on skin appeared to due at least partly to the oxidative stress.     

Variations of skin biophysical properties after recreational swimming

Background/purpose: Sensations of itching and skin tightness are frequently reported after recreational swimming in pool water. Our objective was to measure the potential changes occurring at the skin surface under such conditions.
Methods: Nine women participated in this study, which consisted of two periods. During a 4-day control period, basal biophysical skin parameters were assessed every morning. On the first day, measurements were also performed in the afternoon. The second study period followed the same study design as for the control period, except that, on the first day, women swam for 1 h in a public pool, between the measurements performed in the morning and the afternoon. Skin capacitance, transepidermal water loss, skin temperature, skin pH and sebum casual level (SCL) were measured on facial and body sites.
Results: During the control period, biophysical skin parameters did not show significant variations. By contrast,      h after swimming, biophysical values showed significant changes for all test sites: skin pH increased, whereas skin capacitance and SCL decreased. Biophysical parameters returned to baseline values the day after swimming.
Conclusion: Our results demonstrate that recreational swimming leads to significant transient changes in skin surface properties of women with healthy skin.     

Skin hydration and transepidermal water loss in patients with a history of sulfur mustard contact: a case–control study

Background   Skin lesions are among the most common complications of contact with sulfur mustard.
Objective   This study was aimed to measure skin water content and transepidermal water loss (TEWL) in patients with a history of sulfur mustard contact.
Methods   Three hundred ten male participants were included in this study: 87 (28.1%) sulfur mustard–exposed patients with current skin lesions (group 1), 71 (22.9%) sulfur mustard–exposed patients without skin lesions (group 2), 78 (25.2%) patients with dermatitis (group 3) and 74 (23.8%) normal controls (group 4) The water content and TEWL of skin was measured at four different locations of the body: forehead, suprasternal, palm and dorsum of hand. Nonparametric statistical tests (Kruskal–Wallis) were used to compare the four groups, and P  < 0.05 was considered statistically significant.
Results   The mean age of participants were 44.0 ± 6.7, 41.9 ± 5.9, 43.8 ± 9.3 and 44.8 ± 8.9 years in groups 1 to 4, respectively ( P  = 0.146). Xerosis, post-lesional hyperpigmentation and lichenification were significantly more common in either sulfur mustard–exposed participants or non-exposed participants with dermatitis ( P  < 0.05). Skin hydration was higher in subjects with sulfur mustard contact than in non-injured participants ( P  < 0.05) in the dorsum and palm of hands and forehead. TEWL was significantly higher in participants only in suprasternal area and dorsum of hand.
Conclusion   Contact with sulfur mustard agent can alter biophysical properties of the skin-especially the function of stratum corneum as a barrier to water loss-several years after exposure.

Conflicts of interest

None declared.     

The influence of body mass index on skin susceptibility to sodium lauryl sulphate

Background:   The influence of nutrition on the physiological functions of man is well studied. Numerous diseases can be exacerbated by obesity. However, it has not yet been determined whether body weight and body mass index (BMI), as an indicator of a high body fat store, can influence skin sensitivity.
Objective:   This study investigates the correlation between body mass index and the epidermal functions, evaluated by bioengineering methods, before and after an irritant patch test with sodium lauryl sulphate (SLS).
Methods:   Epidermal functions were evaluated using an evaporimeter, chromameter and laser-Doppler-flowmeter. Patch testing was conducted for 48 h with two different concentrations of SLS (0.25% and 0.5%) on the forearms of healthy volunteers. Measurements were performed 24 h after patch removal.
Results:   Obese individuals showed significantly increased transepidermal water loss (TEWL), skin blood flow and skin colour (red) as compared to a control group. However, the degree of skin sensitivity to SLS was not correlated with BMI.
Conclusion:   Basal biophysical parameters of the skin are primarily correlated with the BMI. This may be caused by obesity-induced physiological changes, e.g. increased sweat gland activity, high blood pressure and physiological temperature-regulating system. The epidermal barrier function, as evaluated after SLS patch testing is, however, not correlated with a high BMI, indicating a normal skin barrier.     

Tribological testing of skin products: gender, age, and ethnicity on the volar forearm

Background/purpose: Few studies have focused on the simultaneous measurement of the friction and electrical properties of skin. This work investigates the feasibility of using these measurements to differentiate between the effects of chemicals commonly applied to the skin. In addition, this study also compares the condition of the skin and its response to application of chemicals across gender, ethnicity, and age at the volar forearm.
Method: Friction and electrical tests were performed on 59 healthy volunteers with the UMT Series Micro-Tribometer (UMT). A 13-mm-diameter copper cylindrical friction/electrical probe was pressed onto the skin with a weight of 20 g and moved across the skin at a constant velocity of 0.4 mm/s. Each volunteer served as his or her own control. The friction and electrical impedance measurements were performed for polyvinylidene chloride occlusion and for the application of glycerin and petrolatum.
Results: No differences were found across age, gender, or ethnicity at the volar forearm. Polyvinylidene chloride (PVDC) occlusion showed a small increase in the friction and a small decrease in the electrical impedance; petrolatum increased the friction by a greater amount but its effect on the impedance was comparable to PVDC occlusion; glycerin increased the friction by an amount comparable to petrolatum, but it decreased the impedance to a much greater degree than petrolatum or the PVDC occlusion. An amplitude/mean measurement of the friction curves of glycerin and petrolatum showed that glycerin has a significantly higher amplitude/mean than petrolatum.
Conclusion: The properties of the volar forearm appear to be independent of age, gender, and ethnicity. Also, the simultaneous measurement of friction and electrical impedance was useful in differentiating between compounds administered to the skin.     

Measuring depth depends on frequency in electrical skin impedance measurements

Background/aims: Multi-frequency electrical measurements in vivo on stratum corneum are frequently reported in the literature. It is well known that the measured volume of skin is dependent on measuring frequency, and we wanted to investigate to what extent viable skin influences the measured impedance as a function of frequency.
Methods: Finite element modelling (FEM) was used to investigate the current and potential distribution in the skin when measuring impedance with two concentric surface electrodes.
Results: The study showed that the impedance measured reflects mainly the stratum corneum at low frequencies, in this case below 1 kHz, and that the viable skin dominates at higher frequencies.
Conclusion: It is concluded that a multi-frequency measurement on isolated stratum corneum is not possible in vivo with conventional techniques, except within a very narrow and low frequency range.