Effects of skin occlusion in patch testing with sodium lauryl sulphate

BACKGROUND: When evaluating transepidermal water loss (TEWL) in patch testing, the occlusive effect of the patch must be considered as an important artificial impairment of the measurement. OBJECTIVES: To investigate the time course of effects of occlusion. METHODS: Epicutaneous patches with sodium lauryl sulphate (SLS) 0.25%, SLS 0.5%, water and an empty test chamber (control) were applied on the volar forearm for different time intervals (12, 24, 48 h). Test reactions were evaluated by measurement of TEWL immediately, every 15 min during the first hour, every 30 min during the following 3 h and 24 h after patch removal. RESULTS: After patch removal, TEWL values showed a steep increase. When compared with basal values, TEWL values after SLS patch testing remained increased for 24 h, whereas TEWL values on water patch sites were only significantly increased for up to 180 min, and on empty patch sites for only up to 120 min after patch removal. The prolonged increase in TEWL values in SLS patch testing seemed to be induced by barrier function damage caused by SLS itself, as shown in various earlier studies. After the initial increase, TEWL values showed a significant decrease for all patches from 0 to 120 min after patch removal. Patch testing with water gave a significant decrease in TEWL values up to 180 min, and for empty chambers (control) up to 150 min after removal of patches. These data suggest that the occlusive effect on TEWL in patch testing ends 3 h after the removal of test chambers. CONCLUSIONS: We recommend TEWL measurement in SLS patch testing after a period of at least 3 h after patch removal. For practical purposes a 24-h period after patch removal may be useful.     

Inhibitory effects of Leopoldine spa water on inflammation caused by sodium lauryl sulphate

BACKGROUND: Sulphur mineral waters may have anti-inflammatory effects on human skin. We evaluated the anti-inflammatory effects of Leopoldine spa water, a salso-sulphate water (Table 1), on human skin tested with sodium lauryl sulphate (SLS). PATIENTS AND METHODS: Ten healthy, Caucasian volunteers 28-53 years old were enrolled in this study. SLS was tested on the right arm, in two concentrations (0.5% and 1%) dissolved in both double-distilled nonpyrogenic water and Leopoldine spa water in four separate test tubes; 0.02 mL of each solution was applied via the testing apparatus (Vand der Bend chambers, four squares measuring 1 x 1 cm), which was fixed and remained in contact with the skin surface. The anti-inflammatory effect was measured via the variations of redness (chromometry, parameter a*), using a Minolta CR 200 chromometer. RESULTS: At base condition the values of a* of the areas that were tested ranged from 7.11 to 9.30 with a mean of 7.97. In regard to the reaction caused by SLS dissolved in double-distilled water, the values of a* ranged from 8.98 to 9.53, mean 9.24, for 0.5% SLS and from 12.81 to 14.33, mean 13.59, for 1% SLS. The a* values for the cutaneous reaction caused by SLS dissolved in Leopoldine spa water ranged from 7.22 to 9.60 (mean 8.20) for 0.5% SLS and from 10.8 to 12.36 (mean 11.68) for the 1% SLS. CONCLUSIONS: These data show the potential anti-inflammatory effects of Leopoldine mineral water on human skin affected by modest inflammatory reactions caused by the direct application of the chemical irritant SLS. Leopoldine spa water can, thus, be considered a natural therapeutic alternative for the treatment of inflammatory skin conditions.     

Effects of glycerol on human skin damaged by acute sodium lauryl sulphate treatment

Glycerol, widely used as humectant, is known to protect against irritants and to accelerate recovery of irritated skin. However, most studies were done with topical formulations (i.e. emulsions) containing glycerol in relatively high amounts, preventing drawing conclusions from direct effects. In this study, acute chemical irritations were performed on the forearm with application of a 10% sodium lauryl sulphate (SLS) aqueous solution under occlusion for 3 h. Then, glycerol aqueous solutions from 1 to 10% were applied under occlusion for 3 h. After elimination of moist excess consecutive to occlusive condition, in ambient air for 15 and 30 min, skin barrier function was investigated by dual measurement of skin hydration and transepidermal water loss (TEWL). Treatments with SLS solution under occlusion significantly increased TEWL and decreased skin hydration as assessed by capacitance measurements. The SLS irritant property was raised by the occlusion and the water barrier function as well as water content appeared impaired. Recovery with glycerol at low doses was remarkable through a mechanism that implies its hygroscopic properties and which is saturable. This precocious effect acts through skin rehydration by enhancing water-holding capacity of stratum corneum that would facilitate the late physiological repair of impaired skin barrier. Thus, glycerol appears to substitute for natural moisturizing factors that have been washed out by the detergent action of SLS, enhancing skin hydration but without restoring skin barrier function as depicted by TEWL values that remained high. Thus, irritant contact dermatitis treated with glycerol application compensate for skin dehydration, favouring physiological process to restore water barrier function of the impaired skin. Empirical use of glycerol added topical formulations onto detergent altered skin was substantiated in the present physicochemical approach.     

Proteomic analysis of skin irritation reveals the induction of HSP27 by sodium lauryl sulphate in human skin

BACKGROUND: There is an increasing need for screening of mild irritants in vitro to reduce animal testing. OBJECTIVES: Proteomics were used to search for new markers of which the expression changes after mild irritation. METHODS: Sodium lauryl sulphate (SLS) was applied topically on excised human skin. Epidermal proteins were isolated from SLS-treated skin specimens that showed hardly any morphological changes. The proteins were analysed by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and proteins that significantly increased or decreased after SLS treatment in a dose-dependent way were characterized by mass spectrometry. Subsequently, immunohistochemistry was performed on skin samples treated with SLS in vivo and nonanoic acid (NAA) or benzalkonium chloride (BC) in vitro to evaluate one of the identified proteins for its predictive value. RESULTS: We identified seven proteins as potentially new epidermal markers for skin irritation. Among these seven proteins, the 27 kDa heat shock protein (HSP27) was identified as the most prominently upregulated protein. A strong nuclear HSP27 staining was seen in the SLS-treated skin, whereas in the vehicle controls only cytoplasmic staining was observed. Moreover, nuclear staining was also observed after topical application of SLS in vivo and after exposure to NAA and BC in vitro. CONCLUSIONS: Our findings suggest that HSP27 may serve as a sensitive marker of skin irritation and eventually as a novel tool in clinics for testing the sensitivity of the patient for a panel of irritants.     

Studies on human skin lymph containing Langerhans cells from sodium lauryl sulphate contact dermatitis.

Immunologic processes in diseased human skin have been extensively investigated, but little is known about the effect of skin diseases on human afferent skin lymph. Starting in the papillary dermis, the skin lymphatics drain the adjacent tissue in a one-way flow toward the regional lymph nodes. The composition of the afferent lymph, therefore, reflects the immunologic inflammatory processes in the drained tissue. To obtain afferent lymph to investigate its content, we inserted a cannula, by means of microsurgery, into a superficial peripheral lymph vessel draining a defined skin area. By manipulating the drained skin area and subsequent examination of the lymph we established an in vivo system for investigating the kinetics of lymph changes during the course of skin reactions. In lymph derived from a mild sodium lauryl sulphate (SLS)--induced contact dermatitis we could demonstrate an increase of both flow and cells. In particular, the number of Langerhans cells (LC) increased enormously during the course of the skin reaction. It, therefore, seems that a large increase in the migration of LC from the skin to the regional lymph nodes is a major feature of SLS-induced contact dermatitis, suggesting that LC may play a major role in the irritant contact dermatitis reaction.     

Variation in barrier impairment and inflammation of human skin as determined by sodium lauryl sulphate penetration rate

BACKGROUND: Skin irritability after a brief exposure to the model skin irritant, sodium lauryl sulphate (SLS), is known to vary considerably between individuals. A difference in the skin barrier to SLS may contribute to this variation. To date, no human in vivo data have been available on SLS penetration into the skin. OBJECTIVES: We studied whether the SLS penetration rate into the stratum corneum (SC) is related to impairment of the water barrier function and inflammation of the skin. METHODS: The penetration of SLS into the SC was assessed using a noninvasive tape-stripping procedure in 20 volunteers after a 4-h exposure to 1% SLS. Additionally, the effect of a 24-h exposure to 1% SLS on the skin water barrier function was assessed by measuring the transepidermal water loss (TEWL). The accompanying inflammation was quantified by measuring erythema. RESULTS: The mean +/- SD diffusivity of SLS (D) and the SLS permeability coefficient (Kp) were 1.4 +/- 0.6 x 10(-8) cm2 h(-1) and 1.5 +/- 0.7 x 10(-3) cm h(-1), respectively. A multiple regression analysis showed that the baseline TEWL, SC thickness and SLS penetration parameters K (SC/water partition coefficient) and D clearly influenced the increase in TEWL after the 24-h irritation test (explained variance: r2 = 0.80). Change in erythema was mainly influenced by SC thickness. CONCLUSIONS: We found that variation in the barrier impairment and inflammation of human skin depends on the SLS penetration rate, which was mainly determined by SC thickness.     

Reactive changes in human epidermis following simple occlusion with water

Reactive changes produced in human epidermis by occlusion with water for 24 or 48 h were studied. A focally widened intercellular space was common. Several, often pronounced, reactive events were observed in the Langerhans cell system, whereas the keratinocytes and the melanocytes seemed unaffected. The reactive events showed a scattered distribution and were revealed only by electron microscopic analysis of extensive section series. It seems that, among epidermal cells, the Langerhans cells are the most susceptible and most easily alerted by an exogenous challenge.     

Increased permeability for polyethylene glycols through skin compromised by sodium lauryl sulphate

In this in vivo human study we assessed the influence of skin damage by sodium lauryl sulphate (SLS) on percutaneous penetration of polyethylene glycols (PEGs) of different molecular weights (MW). Percutaneous penetration of PEGs was determined using tape stripping of the stratum corneum (SC). The forearm skin of volunteers was pretreated with 5% w/w SLS for 4 h, and 24 h later patches with PEGs were applied for 6 h. The penetration parameters were deduced by data regression to Fick's law for unsteady-state diffusion. The trans-epidermal water loss (TEWL) increased after SLS treatment from 6.3 +/- 2.1 to 17.9 +/- 8.7 g/m(2)/h. The diffusion coefficient for all PEGs was increased in the SLS-damaged skin. The increase was smaller for higher MW. In addition, the partition coefficient of PEGs between SC and water was larger in the SLS-compromised skin and showed a tendency to increase with MW. The permeability coefficient decreased gradually with increasing MW of PEGs in both control and SLS-compromised skin. SLS caused a threefold increase in the permeability coefficient for all MWs ranging in control skin from 0.34 to 0.70 x 10(-5) cm/h and in the SLS-compromised skin from 1.20 to 2.09 x 10(-5) cm/h for MW of 590-282 Da. The results of this study show the deleterious effect of SLS on the skin barrier for hydrophilic PEGs. A defective skin barrier will facilitate absorption of other chemicals and local skin effects.     

Effects of all-trans retinoic acid and sodium lauryl sulphate on the permeability of human skin in vitro

Recent in vivo investigations have shown that pretreatment with topical all-trans retinoic acid (RA) may diminish the skin response to sodium lauryl sulphate (SLS). This study evaluated the permeation of SLS through human skin after pretreatment with RA, and vice versa, by in vitro methods. The permeability coefficient of SLS (3.24 ± 0.21 × 10³ cm/h) and the 24-h cumulative amount of SLS (3.41 ± 0.6% of dose applied) permeating RA-pretreated skin did not differ significantly from those across untreated skin (control) (P > 0.05). In contrast, the permeability coefficient of RA (0.23 ± 0.05 × 10³ cm/h) and its 24-h cumulative amount (0.37 ± 0.05% of dose applied) penetrating SLS-pretreated skin were significantly greater than those permeating untreated skin (P<0.05). Thus, an increase in RA penetration was induced by SLS pretreatment; however, pretreating the skin with RA did not inhibit the percutaneous permeation of SLS. Based on previous in vivo findings where RA reduced skin reactions to SLS,⁸ one would speculate that RA pretreatment may decrease SLS penetration. However, these penetration data do not necessarily uphold this presumption. Perhaps, other interactions between the substances and the skin, e.g. at cellular levels, may be responsible for the differing skin responses.     

Differential cytokine expression in skin after single and repeated irritation by sodium lauryl sulphate

Abstract:  In vivo levels of cytokines and presence of neutrophils and eosinophils in skin irritation are not well known. Our objective was to get more insight in inflammatory mediators and markers involved in single and repeated skin irritation. We sampled epidermis-derived fluid using a novel technology that includes application of a negative pressure on the skin after creation of micropores in the stratum corneum by a laser. In nine volunteers, transdermal fluid was sampled after a single 4-h 10% sodium lauryl sulphate exposure and a repeated 3-week exposure (0.1% sodium lauryl sulphate). Twenty-seven cytokines were assessed by multiplex assay, and IL-1α, eosinophil cationic protein and myeloperoxidase by enzyme-linked immunosorbent assay. Levels of eosinophil cationic protein were increased after irritation and correlated with levels of myeloperoxidase. The levels of inflammatory mediators showed large interindividual differences in unexposed and exposed skin. Despite this variation, several mediators clearly showed increased levels: CC chemokine ligand (CCL)11, CXCL10 and vascular endothelial growth factor after both single and repeated exposure, IL-1α and basic fibroblast growth factor after single exposure and interleukin-1 receptor antagonist (IL-1RA) after repeated exposure. After repeated exposure, CCL5 and the ratio IL-1RA/IL-1α both increased compared with single exposure. We conclude that single and repeated irritation induces differential and concerted expression of various inflammatory mediators and markers.     

Additive impairment of the barrier function by mechanical irritation, occlusion and sodium lauryl sulphate in vivo

BACKGROUND: The interaction between potential irritants in the workplace might be important because workers are not usually exposed to a single irritant, but to multiple potentially harmful substances. Physical irritant contact dermatitis caused by friction or mechanical abrasion is a common occupational dermatosis. Prolonged water exposure by occlusion is also common in the workplace. Several studies have revealed the negative effect of the common anionic detergent sodium lauryl sulphate (SLS) on permeability barrier function. OBJECTIVES: To study the additive impairment of permeability barrier function by mechanical irritation combined with 0.5% SLS or prolonged water exposure by occlusion, as models of mild irritation. METHODS: The volar forearms of 20 healthy volunteers were exposed to mechanical irritation and occlusion with water or 0.5% SLS for four consecutive days in a combined tandem repeated irritation test (TRIT). Permeability barrier function was measured with a Tewameter TM 210. Irritation was assessed with a Chromameter CR 300 and a visual score. RESULTS: Barrier disruption in our model was rated as follows: occlusion with SLS and mechanical irritation > occlusion with SLS > occlusion with water and mechanical irritation > mechanical irritation and occlusion with water > occlusion with a glove and mechanical irritation > mechanical irritation > occlusion with water. Barrier disruption caused by occlusion or mechanical irritation was enhanced by the tandem application. The choice of irritant under occlusion, time of occlusion and order of tandem application all affected the degree of barrier disruption. Evaporimetry was able to detect early stages in the development of an irritant reaction before it became visible. Chromametry was not able to detect this early response. CONCLUSIONS: Physical irritants (friction, abrasive grains, occlusion) and detergents such as SLS represent a significant irritation risk and should be minimized, especially when acting together, as shown in our TRIT model.     

Different skin irritation abilities of different qualities of sodium lauryl sulphate

A marked variation in the concentration of sodium lauryl sulphate (SLS) used for irritant patch testing is found in the literature, but is hitherto unexplained. In the present study, 2 different qualities of SLS were tested clinically on healthy volunteers. The skin responses were evaluated by visual scoring as well as by non-invasive measurement of transepidermal water loss (TEWL), blood flow and oedema. A significant difference in the skin response to the 2 qualities was found both clinically and by non-invasive methods used for quantitation. 5 different qualities of SLS were investigated by high-performance liquid chromatography (HPLC). Marked discrepancies in the quantity of C12 carbon chains in the products were found, offering an explanation for the proven difference in the clinical response. It is concluded that only SLS qualities of high purity should be used for irritant patch testing, and that both the quality and the purity of SLS should be stated.     

Susceptibility of atopic dermatitis patients to irritant dermatitis caused by sodium lauryl sulphate.

Basal transepidermal water loss, skin thickness, blood flow and skin colour were examined before and after exposure of 28 patients with atopic dermatitis and 28 healthy controls to sodium lauryl sulphate. Transepidermal water loss was measured with an evaporimeter, skin thickness by ultrasound A-scanning, blood flow by laser Doppler flowmetry and skin colour by a chroma meter using the L*, a* and b* values, respectively. Patients with atopic dermatitis were found to have higher basal transepidermal water loss than controls (p less than 0.0001), and had an inclination towards an increased basal skin thickness (p = 0.056). No statistically significant differences were found with respect to basal blood flow or skin colour. The skin response to sodium lauryl sulphate was found to be statistically significantly increased in atopic patients compared with controls when evaluated by visual scoring and by increase in skin thickness, but not by increase in transepidermal water loss, blood flow or skin colour.     

Dual effects of sodium lauryl sulphate on human oral epithelial structure

Sodium lauryl sulphate (SLS) is a common detergent known to cause irritation and inflammatory reactions in skin. SLS is also the most commonly used toothpaste detergent and has been related to intraoral adverse effects. However, its specific biological effects on the oral mucosa (OM) have not yet been identified. The objective of this study was to investigate the putative effects of SLS on human oral epithelium using a novel in vitro reconstructed three-dimensional cell culture model. Reconstructed human OM, generated from primary normal human oral keratinocytes and fibroblasts, was exposed to clinically relevant concentrations of SLS (range 0.015-1.5%). The cultured tissues were evaluated by histomorphometry, immunohistochemistry (Ki-67, epithelial (E)-cadherin, alpha6-, beta1-integrins, cleaved caspase-3) and the TUNEL method. Increased epithelial thickness, enhanced proliferation (Ki-67), a more pronounced expression of E-cadherin throughout all epithelial cell layers and single TUNEL-positive cells in the middle spinous cell layers were observed in cultures exposed to low concentrations (0.015%) of SLS. At exposure to higher SLS concentrations (>or=0.15%), epithelial thickness, cell proliferation and E-cadherin expression gradually decreased and in the central areas of exposed regions, cells detached from each other and underwent cell death. In conclusion, clinically relevant concentrations of SLS have dual effects on reconstituted human OM; although occasional cell death within the epithelium was also observed, the increased epithelial thickness, proliferation and E-cadherin expression induced at lower concentrations might be associated with a protective mucosal response, whereas at higher concentrations a more destructive type of reaction predominated.     

Time course of occlusive effects on skin evaluated by measurement of transepidermal water loss (TEWL) Including patch tests with sodium lauryl sulphate and water

The time course for transepidermal water loss (TEWL) for a period of 3 h after removal of occlusive patch tests with sodium lauryl sulphate (SLS), water and empty chambers was studied in healthy volunteers. Patches were applied to the upper arm for 24 h, TEWL was measured immediately after removal of the patches, and every 30 min up to 3 h. For SLS and water patches, TEWL remained significantly increased for 3 h. as compared to normal adjacent skin, while for empty chamber patches. TEWL was only significantly increased for 30 min. A significant decrease from 0 to 30 min and from 30 to 60 min was observed for all patches, and for water patches, a significant decrease in TEWL was found from 60 to 180 min, while SLS patches remained constant. The prolonged increase in TEWL observed after SLS exposure is a well-known occurrence. The prolonged increase in TEWL after exposure to water is interpreted as transient damage to the water harrier of the skin.     

Electrical impedance measured to five skin depths in mild irritant dermatitis induced by sodium lauryl sulphate

The non-invasive electrical impedance technique used in this study reflects structural changes in a tissue, and provides an estimate of the level of oedema by a simple impedance index. Sodium lauryl sulphate (SLS), dissolved in water at concentrations of 0.1, 0.5 and 2.0%, was applied for 24 h in 12 mm Finn chambers® on both volar forearms of 12 healthy volunteers. An unoccluded area was used as a reference site. Readings from all sites were taken before the application of the irritant, and 24 h after its removal. After the last reading, a 3-mm punch biopsy was taken from each test site for histological examination. The results obtained from electrical impedance measurements at five different skin depths were correlated with those obtained from histological examination, visual scoring and transepidermal water loss (TEWL). For all of the methods used the responses were proportional to the concentration of the irritant. Statistically significant changes of electrical impedance were found for all depths and concentrations, except for 0.1% SLS at the most superficial depth. The histological changes were focused in the epidermis, and mainly consisted of oedema. Alterations in the thickness of the epidermis due to oedema were used as a quantitative parameter for correlation with the assessment of irritation using the electrical impedance technique. For the detection of irritant reactions, TEWL and electrical impedance are more sensitive than visual scoring, and selection of the optimum depth penetration further increases the sensitivity of the electrical impedance measurement.     

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.     

Sodium lauryl sulphate penetration in an in vitro model using human skin

Because of their ability to impair the skin barrier function, detergents constitute a major risk factor for the development of irritant contact dermatitis. Sodium lauryl sulphate (SLS) is a commonly used detergent for experimental studies within the area of irritant contact dermatitis. In the present study, penetration of S³⁵-labelled SLS was studied in an in vitro model using human cadaver skin. The investigations showed that SLS is capable of permeating the skin barrier when applied under occlusion. SLS could be detected in the dermis and the amount of SLS found here was shown to depend on the dose of SLS applied on the skin. Penetration of SLS continued after removal of the SLS applied as a patch test on the skin surface. Considerable inter-individual variation in the penetration of SLS was demonstrated between different donors.