Bioengineering and the patch test

Howard I. Maibach: Extraordinary Leadership in Integrating Key Concepts Underpinning Our Understanding of Percutaneous Absorption and Occupational Dermatology

The purpose of the present article is to briefly highlight some contributions of Prof. Howard I. Maibach to the field of dermatology. After a few introducing remarks regarding Howard's personal career, the article specifically reviews contributions to the understanding of percutaneous absorption and to occupational dermatology. He and his companions/coworkers established and introduced experimental prerequisites to better study and understand percutaneous absorption - both in vitro and in vivo. Not less influential was his contribution to occupational dermatology acting as a founding member of the International Contact Dermatitis Research Group and coinaugurating the North American Contact Dermatitis Group. These groups have been very active ever since. As an academic teacher, he inspired young colleagues to perform original research work and to establish their own working groups. He has done this most successfully with many fellows who worked with him over the years, and who are now leading departments or companies dedicated to dermatological research all over the world. Probably this is his most important and lasting achievement.

Capacitance, transepidermal water loss and causal level of sebum in healthy subjects in relation to site, sex and age

Summary To determine normal levels of transepidermal water loss (TEWL), capacitance and sebum according to different sex and age groups, 93 healthy subjects were studied at 14 different anatomical locations with three different instruments: the Evaporimeter EP 1, the Corneometer CM 820, and the Sebumeter SM 810, evaluating respectively the transepidermal water loss, the capacitance and the causal level of sebum. Differences depending on the anatomical site were noticed. Unlike the capacitance, the transepidermal water loss and the causal level of sebum significantly decreased according to age. Furthermore, in some sites, male subjects showed a significantly higher transepidermal water loss than females, while hydration of the horny layer expressed by the capacitance showed an opposite trend. Correlations between the above-mentioned skin parameters were calculated: a positive correlation between TEWL and hydration was observed only at plantar and palmar areas.

Percutaneous Penetration of Methyl Nicotinate from Ointments Using the Laser Doppler Technique: Bioequivalence and Enhancer Effects

Laser Doppler flowmetry (LDF) may be used to quantify erythema response as a result of an increased cutaneous microcirculation induced by methyl nicotinate (MN). Bioequivalence of a test and a standard preparation (vehicles: light mineral oil and medium chain triglycerides, respectively) was confirmed according to the pilot study of the FDA Guidance for Industry "Topical dermatologic corticosteroids: In Vivo bioequivalence" applying the staggered application and synchronized removal method for one defined concentration. Furthermore, the influence of penetration enhancers (5% w/w Dimethylsulfoxide (DMSO) and 10% w/w diethylene glycol monoethyl ether) on MN penetration was investigated. It was shown that DMSO and diethylene glycol monoethyl ether altered cutaneous microcirculation and thus MN penetration in comparison to the standard formulation. However, true penetration enhancement could only be proved with diethylene glycol monoethyl ether resulting from an improved drug solubility in the skin which was confirmed by attenuated total reflectance fourier transform infrared spectroscopy (ATR-FTIR). Increased MN penetration by DMSO was only caused by thermodynamic effects, i.e. a decreased drug solubility in the vehicle.

Macro-video documentation patch tests

An unequivocal distinction between allergic and irritant patch test reactions is often difficult with patch tests. This study was designed to evaluate the worth of video-macro camera documentation for differentiation between allergic and irritant test reactions and to investigate whether there are characteristic clinical differences in patch test responses between metal salts and fragrances. Patch testing was performed with nickel sulfate, fragrance mix and an irritant, sodium lauryl sulfate 1% aq., on the upper back of 82 patients, with evaluation and computer-aided video documentation after 48 and 72 hr. No reliable clinicomorphological criterion was found for assessing a weak patch test reaction as being definitely allergic. Even characteristic papules and vesicles were not regularly found in allergic reactions. However, unlike fragrance mix, patch test reactions to nickel sulfate were characteristic in that they showed a heterogeneous spread and an association with hair follicle openings, independent of reaction intensity. Evaluation based on additional computer-aided video-macro camera documentation did not add further advantage for the differentiation of allergic and irritant reactions. But well-defined clinicomorphological features and reaction patterns to single test substances or even whole substance categories could be helpful additional criteria for evaluating patch test responses in clinical practice.

Objective interpretation of severity of SLS induced edema by stereoimaging

BACKGROUND

In the evaluation of the severity of skin inflammations, visual scoring system is widely being used as a subjective method. However, it is well known that interobserver variations occur even between the interpretations of experienced dermatologists.

OBJECTIVE

To develop a new objective and quantitative method for the evaluation of skin surface contours and for the assessment of severity in SLS-induced edema, a new investigatory tool based on the concept of "stereoimaging" was studied. Differences between binocular images were used by a stereoimage optical topometer (SOT) system capable of calculating skin surface topographic information, which was then used to produce a three-dimensional image.

METHODS

We compared the results obtained by SOT with a visual scoring system after applying sodium lauryl sulfate (SLS) to skin. The degree of edema was assessed qualitatively by visual scoring (0: none, 1: mild edema, 2: moderate edema, 3: severe edema). To quantify the severity, five three-dimensional parameters (S(a), S(z), SL, SA and SV) were used in the SOT analysis.

RESULTS

The means of these five parameters increased significantly in visual grade 1+ compared to visual grade 0 and the means of the five parameters decreased significantly and proportionally as the visual grades increased from 1+ to 3+. A highly significant correlation was found to exist between the visual scoring results and the five SOT parameters.

CONCLUSION

SOT can be used to evaluate the severity of SLS-induced edema objectively and can be extensively applied to evaluate the degree of severity in other inflammatory skin conditions.

Fiber optic near-infrared Raman spectroscopy for clinical noninvasive determination of water content in diseased skin and assessment of cutaneous edema

Currently, measuring Raman spectra of tissues of living patients online and in real time, collecting the spectra in a very short measurement time, and allowing diagnosis immediately after the spectrum is recorded from any body region, are specific advantages that fiber optic near-infrared Raman spectroscopy (NIR RS) might represent for in vivo clinical applications in dermatology. We discuss various methodological aspects and state of the art of fiber optic NIR RS in clinical and experimental dermatology to outline its present advantages and disadvantages for measuring skin in vivo, particularly its water content. Fiber optic NIR Fourier transform (FT) RS has been introduced to dermatological diagnostics to obtain information regarding the molecular composition of the skin up to several hundred micrometers below the skin surface in a relatively fast nondestructive manner. This has been especially important for probing for in vivo assessment of cutaneous (intradermal) edema in patients patch test reactions. Fiber optic NIR FT Raman spectrometers still require further technological developments and optimization, extremely accurate water concentration determination and its intensity calculation in skin tissue, and for clinical applications, a reduction of measurement time and their size. Another promising option could be the possibility of applying mobile and compact fiber optic charge-coupled device (CCD)-based equipment in clinical dermatology.

In vivo investigation, in mice and in man, into the irritation potential of novel amphiphilogels being studied as transdermal drug carriers

Amphiphilogels, gels that consist solely of non-ionic surfactants, are being developed as dermal/transdermal drug delivery vehicles in our laboratories. The irritation potential of two amphiphilogels was investigated on shaved mouse skin, in vivo, and compared to those of Aqueous Cream BP (a moisturiser) and 5% sodium lauryl sulphate (SLS) solution (a known irritant). The skin irritation potential of one of these gels was then investigated in human, using Aqueous Cream BP as a negative control. Skin irritation (following daily application of gels and of controls for 5 days) was assessed by laser Doppler velocimetry, a visual erythema scoring method, and histological evaluations of excised mice skin. We found that the amphiphilogels caused no significant increase in blood flow and in epidermal irritation. In contrast, the SLS solution caused significant perturbation to mouse skin. From this study we conclude that these amphiphilogels may be used as dermal/transdermal drug delivery vehicles.

Quantitative evaluation of severity in psoriatic lesions using three-dimensional morphometry

The severity of psoriasis has been traditionally assessed by measures, such as the psoriasis area and severity index (PASI), the psoriasis severity scores, and the lesional severity scores. As a result, even experienced dermatologists show variations when attempting to determine the severity of psoriasis. Therefore, a better non-invasive and objective measurement of clinical signs is needed. In this study, an instrument, a so-called 'stereoimage optical topometer' (SOT), based on a new concept of 'stereoimaging' was used to measure the three-dimensional skin surface. The aim of this study was to compare the results obtained by the SOT with the visual score of psoriasis lesion. Thirty psoriatic patients were enrolled in this study. Initially, the severity of the infiltration and the scale of 134 psoriatic lesions were assessed by using a visual scoring system (0: none, 1: mild, 2: moderate, 3: severe, and 4: very severe), as scored by five dermatologists. The SOT was then used to quantify the severity of each psoriatic lesion using four three-dimensional SOT parameters (Sa, SL, SA, and SV). Secondly, the involved skin-surface area in the psoriasis cases was scored by the naked eye by the five dermatologists and by image analysis. Statistically significant differences were observed between grades 0, 1, 2, and 3 in terms of the severity measurements of the individual psoriatic lesions by SOT when using the parameters Sa, SL, SA, and SV. Therefore, it was concluded that there is a strong correlation between the results measured by visual scoring and by SOT in psoriasis.

Artificial disruption of skin barrier prior to irritant patch testing does not improve test design

BACKGROUND

Irritant patch testing is often performed as a 24- or 48-h occlusive patch test with low concentrations of sodium lauryl sulphate (SLS).

OBJECTIVES

The aim of this study was to investigate potential ways to shorten this test procedure and obtain precise test results.

PATIENTS AND METHODS

Thirty-six healthy volunteers underwent irritant patch testing with different pretreatments (PT) of the test fields. Occlusive test chambers were applied on the upper back with SLS 0.5%, 1%, 2% and 5% in large Finn Chambers(R). The patches were removed after 4 and 24 h, respectively, depending on the concentration used. Test fields were pretreated as follows: PT 0, field without any PT (control); PT 1, prick with lancet; PT 2, prick with test stamp; PT 3, scratch with lancet; PT 4, incision with standardized incision instrument (0.1-0.2 mm depth). Skin reactions were evaluated by transepidermal water loss (TEWL), skin erythema and skin hydration and as well by a visual score (VS) at 4, 24 and 72 h.

RESULTS

Our data show an obvious distinction between PT 0-2 and PT 3-4 at all measurement methods. The average TEWL values with PT 3-4 were higher than those with PT 0-2, especially on the 4-h course. This distinction may derive from the shape and size of the skin impairment achieved by PT 3-4, leading to a mechanical barrier disruption. However, SLS may infiltrate directly into deeper skin layers supported by capillarity. Consequently, no or little penetration through the epidermis and interaction with its structures occurs, which is responsible for irritant skin reactions. The SLS dose in the upper skin layers is therefore lower at these PTs. The lower remaining dose of SLS also explains this distinction, especially for the VS. Additionally, there are presumed reactions in deeper layers of the epidermis and dermis at PT 3-4.

CONCLUSIONS

In summary, all data suggest a different reaction pattern from the classical irritant response. Therefore, application without any PT seems to be best suited for irritancy skin testing, especially for visual assessment. PTs prior to irritant patch testing have been shown to be unjustifiable.

Electrical impedance as a potential tool to distinguish between allergic and irritant contact dermatitis

BACKGROUND AND OBJECTIVE

The allergic contact reaction is a model reaction for studying the cell-mediated immune system of the skin. In this study we use a noninvasive method, electrical impedance (IMP), to compare nickel (Ni) allergic contact reactions with an irritant contact reaction induced by sodium lauryl sulfate, which has already been carefully evaluated with this method. For this purpose, we included only Ni- and sodium lauryl sulfate-induced reactions of very similar appearance.

METHODS

Various concentrations of Ni sulfate in distilled water were applied on the volar aspect of the forearms of 33 adult women who were allergic to Ni. Assessments were made using visual scoring, a new IMP technique, and transepidermal water loss 3 and 7 days later.

RESULTS

In the 19 patients who completed the study, 3 of the 4 impedance indices were significantly lower at the sodium lauryl sulfate sites than at the Ni sites on day 3; ie, the mean magnitude (MIX) (P < or = .001), imaginary part (IMAX) (P < or = .001), and real part (RIX) indices (P < or = .01). Unlike the irritant reactions, no significant increases in transepidermal water loss occurred in the allergic contact reactions. This may be because, in reactions of the studied magnitude, an allergic contact reaction does not significantly affect the epidermis because the inflammatory process is located deeper in the dermis than an irritant reaction.

CONCLUSION

This study suggests that IMP, as used herein, is suitable for distinguishing between contact reactions of allergic and irritant nature. Although pathophysiologic events in the tissue studied significantly modify impedance patterns, little is known about how to interpret the structural and chemical changes underlying these patterns. Studies are needed to determine the relation between anatomic or pathophysiologic parameters, and the findings using IMP and other established methods, such as chemical extraction and histopathology.

Skin permeation enhancement effect and skin irritation of saturated fatty alcohols

Though the skin permeation enhancement effect of chemical penetration enhancers has been studied extensively, their skin irritation potential has not been adequately investigated. The objective of this study was to evaluate the skin permeation enhancement effect and skin irritation of saturated fatty alcohols using melatonin as a model compound. A saturated solution of melatonin in a mixture of water and ethanol (40:60) containing 5% w/v of saturated fatty alcohol was used in the skin permeation studies using Franz diffusion cells. For skin irritation studies, 230 microl of fatty alcohol solution was applied on the dorsal surface of the hairless rats using Hill top chamber. The skin irritation was evaluated by visual scoring method and bioengineering methods such as measurement of transepidermal water loss (TEWL) and skin blood flow. The flux of melatonin across hairless rat skin was found to be dependent on the carbon chain length of the fatty alcohols, with decanol showing the maximum permeation of melatonin. All fatty alcohols increased the TEWL and skin blood flow significantly compared with the vehicle. The fatty alcohols (decanol, undecanol and lauryl alcohol), which showed greater permeation of melatonin, also produced greater TEWL, skin blood flow and erythema. Tridecanol and myristyl alcohol showed lower permeation enhancement effect but caused greater skin irritation. Octanol and nonanol may be the most useful enhancers for the transdermal delivery of melatonin considering their lower skin irritation and a reasonably good permeation enhancement effect. However, further studies are needed to ascertain their safety as skin penetration enhancers. Skin permeation and skin irritation in experimental animals such as rats are generally higher compared with human skin. Further studies in human volunteers using fatty alcohols at the concentrations of 5% or lower may provide useful information on the utility of these fatty alcohols as permeation enhancers.

A pilot study of noninvasive methods to assess healed acute and chronic wounds

BACKGROUND

A variety of instruments are available that can objectively assess physical parameters of the skin such as strength, firmness, elasticity, hydration, and color, often undetected by clinical assessment.

OBJECTIVE

To assess the physical properties of healed acute and chronic wounds using several noninvasive instruments.

METHODS

Four patients with healed acute wounds and four patients with healed chronic wounds were studied using ballistometric, impedance, levarometric, and spectrophotometric measurements.

RESULTS

In general, scars were harder, less elastic, dryer, and more erythematous than control skin. These differences were more pronounced in healed chronic wounds.

CONCLUSION

A scar from an acute surgical wound becomes softer, more elastic, dryer, less erythematous, and less pigmented as it ages. In contrast, chronic wound scars become harder as they age. These different properties of healed acute wounds and healed chronic wounds may be a result of the different healing processes in each wound type.

Assessment of budesonide patch tests

Patch-test technique for budesonide needs improvement. 20 subjects with positive or questionable patch-test responses to budesonide were retested for 3 to 96 h (4 days [D]) with polyester patches coated with budesonide in serial doses (150 to 0.074 microg/cm2). Multiple readings were taken visually and with a laser Doppler perfusion imaging technique up to 264 h (day [D]11). Additionally, all subjects were tested with 0.1% budesonide in petrolatum in Finn Chambers for 48 h (2D) with readings taken at 72 (D3), 96 (D4) and 168 h (D7). Different dose levels and application times affected unpredictably highest assessments of reactions. No clear suppression of reactivity was observed at high doses. Time points of highest assessments of reactions varied between subjects but were generally the same for each subject with both reading methods regardless of dose levels or application times. Positive and negative subjects during the study were easily distinguished with all serial doses, regardless of assessment technique. At 2.0 microg/cm2, the lowest dose level tested on all subjects, longer applications than 24 h (1D) were required to detect all positive subjects. 48-h (2-D) applications required 2 readings, optimally at 96 (D4) and 216 h (D9). The only test technique with Finn Chambers used here did not make such distinction possible.

In vivo nickel allergic contact dermatitis: human model for topical therapeutics

Techniques to determine efficacy of topical agents on allergic contact dermatitis (ACD) may benefit from refinement. The aim of this study was to develop an in vivo human model system for the bioengineering and visual quantification of the effect of topical agents on nickel ACD, and to correlate ACD parameters. 14 nickel patch-test-positive subjects were included in a placebo-controlled, double-blind study after a pre-screening procedure with a standard diagnostic patch test with nickel sulfate in 54 healthy human volunteers. 5% nickel sulfate in petrolatum in a Finn Chamber was applied on forearm skin for 48 h to create a standardized dermatitis. Thereafter, the dermatitis was treated with a model topical agent and a placebo control while recording endpoint parameters daily for 10 days. Resolution was quantified with 4 parameters: visual scoring (VS), transepidermal water loss (TEWL) (Tewameter), skin blood flow volume (BFV) (laser Doppler flowmeter), and skin color (a* value) (Colorimeter). The model agent reduced cutaneous allergic reactions, especially on day 8 to 10, in comparison with the placebo control. A highly significant linear relationship exists among all parameters, except between a* and BFV. This model may provide robust biometrics for determining the efficacy of topical therapeutics on experimentally induced ACD.

In vivo human skin permeability enhancement by oleic acid: a laser Doppler velocimetry study

Topical application of a skin permeation enhancer such as oleic acid (OA) can result in: (i) higher skin permeability for many exogenous substances (ii) an irritation reaction. Laser Doppler velocimetry (LDV) is one of few techniques which can assess both effects using appropriate protocols. Direct LDV measurement, measuring cutaneous blood flow, has been preferred as a tool to evaluate skin irritation. By comparing the LDV value of an irritant-treated site with an untreated site, an irritation index for the irritant can be obtained. Occlusive application of 0.16 M OA in propylene glycol (PG) for either 3 or 24 h produced irritation in form of redness and slight swelling. Using LDV, we obtained an irritation index of 2 and 4, respectively. The vehicle, PG alone, produced an index of around 1, which corresponded well to the slight to almost no irritation observed visually. The duration of the high irritation index assessed by LDV after OA-PG application is comparable to the duration of the increase in transepidermal water loss following the same application. This indicates a correlation between skin irritation and barrier perturbation caused by OA. LDV can also be used to elucidate the effect of enhancers on skin using hexyl nicotinate (HN) as a model drug, since its vasodilative effect can be clearly assessed by LDV. Pre-treatment of PG for 3 h significantly reduced the t0 and tmax of HN. No further reduction could be observed when OA was added into PG, suggesting that OA-PG is not more effective than PG alone in enhancing the permeation of HN.

Loss of contact sensitization evaluated by laser Doppler blood flowmetry and transepidermal water loss measurement

Allergic contact dermatitis, which is mediated by activated T cells through a Type IV reaction, is usually believed to persist throughout life. There have been several reports of spontaneous loss of sensitization, e.g., loss of previous patch test reaction or loss of allergic contact dermatitis withal continuous exposure to the allergens. However, these have been well quantified. The aim of this study was to confirm the development of desensitization or hyposensitization with the aid of objective measurements. A total of 18 patients with alopecia areata, who received 4 months diphenylcyclopropenone (DPCP) contact immunotherapy, were patch tested and the responses were measured by laser Doppler blood flowmetry (LDF) and transepidermal water loss (TEWL). Patch tests were performed 2X, before and after 4 months of immunotherapy. To determine whether local desensitization developed, we compared change of DPCP concentrations producing mild contact dermatitis on the scalp. Our results showed that systemic and local hyposensitization occurred in human subjects by weekly applications of low concentrations of DPCP for 4 months. LDF seems to be more correlated with visual scores than TEWL measurement.

Skin irritation in man: a comparative bioengineering study using improved reflectance spectroscopy

Variable types of skin irritation were induced in 8 human female volunteers, ranging from subclinical to visible erythema with slight oedema. Skin reactions were graded clinically and objectively using transepidermal water loss (TEWL), laser Doppler flowmetry (LDF) and improved reflectance spectroscopy. This last technique enables separation of in vivo erythemas into relatively deoxygenated (venous--deoxy hem) and oxygenated (arterial--oxy hem) haemoglobin components. Compared to uninvolved skin, an empty patch increased oxy hem by 197% +/- 121% (p < 0.05). Exposure to vehicles also changes skin biophysics. At sodium lauryl sulfate (SLS) and hydrochloric acid (HCl) exposed sites, a linear correlation between concentration and oxy hem, LDF and TEWL was found. These chemicals predominantly increased TEWL values. Nonanoic acid (NON) and imipramine (IMI) also raised oxy hem, LDF and TEWL values linearly at increasing concentrations. Although IMI 2.5% clinically was graded as a type ++ response, no significant increase in TEWL was found. The improved reflectance spectroscopic technique proved valid in skin irritation studies, with a higher sensitivity than laser Doppler flowmetry, and allowed irritant vascular reactions to be discriminated into arterial and venous components. Furthermore, our observations clearly demonstrate that clinically indistinguishable skin irritation reactions induce significantly different changes in barrier function (disruption) and vascular status.

The sodium lauryl sulfate model: an overview

Irritant contact dermatitis is a complex entity with several clinical forms (acute, cumulative, etc.) and multiple mechanisms. Sodium lauryl sulfate (SLS), the most widely utilized model for studying acute and cumulative irritation, has proved highly practical and informative for such studies. This article summarizes several decades of investigation, and provides details of dosing, application method (closed versus open), and biologic endpoints (visual grading, transepidermal water loss) that may be utilized in future studies.

Study of cumulative irritant contact dermatitis in man utilizing open application on subclinically irritated skin

We evaluated the effect of subclinical irritation on the cutaneous reaction elicited by cumulative short-term (30-min) application of sodium lauryl sulphate (SLS), by measuring transepidermal water loss (TEWL) and assigning visual scores. 11 healthy adult volunteers, free of skin disease and with no history of atopic dermatitis, were treated with SLS solution (1%, 2%, 5%, 7.5%). On a Monday, we applied 80 microliters of 1% SLS solution and deionized water (control), using large aluminium chambers with filter paper discs, for 30 min. We measured TEWL values 2 x before and after patch application of control and 1% SLS solution, and then applied 80 microliters of SLS solution (2%, 5%, 7.5%) using filter paper discs. From Tuesday to Friday, we applied 80 microliters of each solution, using filter paper discs, and measured TEWL before and after open application of test solutions. Compared with each corresponding group, TEWL values of SLS patch groups (S-2.0, S-5.0, S-7.5) were higher than those of water patch groups (W-2.0, W-5.0, W-7.5), respectively. TEWL values of each groups increased stepwise and the final (hour 97) TEWL values were higher than those of baseline (hour 0) TEWL. The mean visual scores of the vehicle control were lower than those of other test groups, but there were no statistically significant differences in visual scores between each test group. These findings suggested that impaired skin barrier function, elicited by subclinical irritation from short-duration contact with some irritants, might augment the cumulative irritant contact dermatitis caused by repeated open exposure to other surfactants.(ABSTRACT TRUNCATED AT 250 WORDS)

Efficacy of skin barrier creams (II). Ineffectiveness of a popular "skin protector" against various irritants in the repetitive irritation test in the guinea pig

A popular "skin protector" consisting of an emulsion-like foam of lipophilic and hydrophilic substances (Marly skin) was evaluated in a previously described repetitive irritation guinea pig model. The product failed to inhibit the irritation due to sodium lauryl sulphate and toluene. In striking contrast to the recommended use, the irritant response of sodium hydroxide was aggravated, as demonstrated by significant differences for all test parameters (clinical score for erythema and scaling, transepidermal water loss, blood flow volume). The results show that protection against chemical irritants may be quite specific and that some formulations may actually be harmful.

Efficacy of skin barrier creams (I). The repetitive irritation test (RIT) in the guinea pig

An animal model for the evaluation of skin protective creams against chemical irritants is described. The irritants were applied daily for 2 weeks to shaved back skin of young guinea pigs: sodium lauryl sulphate (5% aq.; 30 min), sodium hydroxide (0.5% aq.; 2 min), and toluene (20% eth.; 2 min). The barrier cream was applied 2 h prior to and immediately after exposure to the irritant. Control animals were treated with the irritant only. The irritant reaction was scored on a 4-point scale for erythema and quantified with regard to transepidermal water loss (TEWL) by evaporimetry and skin blood flow volume (BFV) by laser Doppler velocimetry. A total of 90 guinea pigs, consisting of individual panels of 5 to 10 animals, was tested. While one barrier cream (Stokoderm) significantly suppressed the irritation due to sodium lauryl sulphate and toluene, the other (Contra-Alkali) failed to do so and even aggravated the response, which was particularly evident with sodium hydroxide. This model may be useful in developing more effective barrier creams.

Loss of lanolin patch-test positivity

Thirty-seven patients who had shown a relevant positive patch-test response to lanolin within the previous 5 years were retested. Only 41% demonstrated persistence of the positive patch test to lanolin. Analysis according to age, sex, atopic status, interval between patch testings, strength of the original response and the number of concurrent reactions, were not associated with the persistence of the lanolin response.

Sequential order of skin responses to surfactants during a soap chamber test

Differences in the response of distinct layers of the skin to surfactants were probed using a modification of the Frosch and Kligman soap chamber test. Soap and other surfactant-containing cleansers were applied to the skin for 2 consecutive days. Transepidermal water loss showed that the stratum corneum is readily damaged even by a mild insult when no erythema is induced. A more severe treatment, such as 24-h exposure to a 5% soap solution, induced the maximal level of barrier damage but a submaximal level of erythema. Even 2 days of exposure to 5% soap does not elicit a maximal erythema response. These results suggest that the stratum corneum is more readily damaged than the dermis, which is not unexpected because the stratum corneum is the initial point of contact between surfactant and skin. Furthermore, this study indicates that for discriminating among mild products, when a small degree of irritation is induced, the most effective measure is stratum corneum damage assessed by evaporimetry. However, for evaluating more irritating products, erythema is probably the more discriminating evaluation technique.

Ultrasound B scanning with image analysis for assessment of allergic patch test reactions

Assessment of patch test results has been performed visually and using ultrasound in the B mode. A positive test site has a typical ultrasonographic appearance, presenting a uniform hypoechogenic area in the dermis. In this zone, the mean amplitude of ultrasound reflection peaks decreases, and the extension of this area increases, together with the intensity of the eczematous reaction. A close correlation has been shown between visual scoring, amplitude decrease and surface increase of the hypoechogenic area. This technique seems to provide a reproducible system for the evaluation of patch tests.

Sodium lauryl sulfate-induced irritant contact dermatitis in vulvar and forearm skin of premenopausal and postmenopausal women

Reactivity of the skin of the forearm and labia majora to three concentrations (2%, 3%, 5%) of sodium lauryl sulfate was studied in 20 healthy women, 10 premenopausal and 10 postmenopausal. Patches with the irritant were applied on day 0 for 24 hours. Skin changes were monitored by visual scoring and by the measurement of transepidermal water loss and capacitance as indicators of stratum corneum hydration on days 2, 3, 7, and 10. In forearm skin, irritant dermatitis developed in the majority of subjects as indicated by visual scoring and increase of transepidermal water loss. These changes were not significantly dependent on the concentration of sodium lauryl sulfate. In labia majora skin, irritant dermatitis developed in 50% of the women as determined by visual scoring; however, because of the pigmentation, visual scoring readings were less reliable in labia majora skin. Transepidermal water loss did not increase, but a significant and immediate decrease in capacitance was noted in labia majora skin. In forearm skin, postmenopausal women reacted less frequently and more slowly to sodium lauryl sulfate than premenopausal women whereas no age-related differences were observed in reaction of the vulvar skin. It is concluded that labia majora skin is not more reactive to sodium lauryl sulfate than forearm skin and that capacitance is more sensitive than transepidermal water loss in monitoring vulvar irritant dermatitis. Age-related differences in irritant reaction are apparent in the forearm, but not the vulva.

Multiple parameter assessment of vulvar irritant contact dermatitis

Transepidermal water loss (TEWL), capacitance, pH, blood flow and color reflectance were evaluated for quantifying the irritant response of vulvar and forearm skin to 3% sodium lauryl sulfate in 9 healthy premenopausal women. TEWL, capacitance, pH, blood flow, and all parameters of color reflectance changed significantly in forearm irritant dermatitis. In vulvar irritant dermatitis, however, significant changes were observed only for blood flow and the color reflectance parameters a* and b*. Using the combination of TEWL, capacitance and blood flow, forearm irritant dermatitis was detected with a sensitivity of 84% and a specificity of 100%. In this study, the best combination of parameters to detect vulvar irritant dermatitis was pH, blood flow, a* and b*, which had a sensitivity of 78% and a specificity of 75%. It is concluded that available bioengineering techniques are less suitable to quantify irritant dermatitis in the vulva than in the forearm.

Guidelines for transepidermal water loss (TEWL) measurement. A report from the Standardization Group of the European Society of Contact Dermatitis

This report reviews individual-related variables, environment-related variables and instrument-related variables, with a focus on the Evaporimeter EP1 (ServoMed). Start-up and use is described, and guidelines for good laboratory practice given.

Skin reactions to irritants assessed by non-invasive bioengineering methods

Pathophysiological components of irritant contact dermatitis caused by 3 chemically-different irritants were investigated. 20 healthy volunteers were patch tested with sodium lauryl sulphate, nonanoic acid and hydrochloric acid on the flexor side of the upper arm. The skin response was evaluated after 24, 48 and 96 h by visual scoring and measured by the following bioengineering methods: transepidermal water loss measurement, electrical conductance for measurement of skin hydration, laser Doppler flowmetry for measurement of cutaneous blood flow and 20 MHz ultrasound A-scan for measurement of skin thickness. In spite of homogeneous inflammatory responses, significant differences in the severity of the injury to the skin barrier function caused by the different irritants were found. Also significant differences between irritants were found in the time course of development of maximum irritant reactions. Bioengineering methods indicating inflammatory responses (measurement of blood flow and skin thickness) were helpful in quantifying the irritant response in general, while bioengineering methods indicating epidermal damage (measurement of TEWL and electrical conductance) were helpful in classifying the individual irritants.