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A Controlled, Three-Part Trial to Investigate the Barrier Function and Skin Hydration Properties of Six Skin Protectants
The superficial layer of the skin, the stratum corneum, provides a protective barrier. This layer consists of keratin-filled corneocytes organized in a matrix of highly ordered multilamellar lipid sheets, described as a brick wall-like structure (the corneocytes forming the bricks and the intercellular lipids representing the mortar).1 If the stratum corneum breaks down, the barrier function of the skin is impaired, a risk factor associated with the formation of pressure ulcers.2,3
Factors that can impair barrier function include irritants, moisture, abrasion, and biological influences that result in dry, compromised skin. Patients with incontinence are at particular risk for barrier impairment. If untreated or poorly managed, incontinence will impair the barrier, predominately due to skin maceration but also as a result of irritants and abrasion from bed linens. A review article on current practices and principles for skin care of frail, elderly, dependent, patients with incontinence4 reported that fecal incontinence is a greater risk factor for skin breakdown than urinary incontinence. Another review, published by the Canadian Association of Wound Care,5 indicated that maceration of the skin via fecal or urinary incontinence causes skin breakdown and pressure ulcers and included 12 recommendations for best practices in the prevention and treatment of pressure ulcers that focus on an interdisciplinary, patient-centered approach.
Managing patients with incontinence commonly involves skin protectant use. An understanding of diaper dermatitis and its treatment in infants6 has yielded valuable information regarding incontinence dermatitis.6,7 Irritant diaper dermatitis (IDD), a form of contact dermatitis, occurs in the diaper area as a consequence of disrupting the skin’s barrier function through prolonged contact with feces and urine. The available evidence8 suggests that maceration of the stratum corneum by water increases susceptibility to frictional damage and epidermal permeation of irritants. The most important irritants underlying IDD are the proteolytic digestive enzymes persisting in feces, particularly when activated by the high pH of urine. The stratum corneum barrier itself is broken down further by ceramidase enzymes secreted by Candida spp. and Staphylococcus aureus.
The ensuing penetration of endotoxin activates the inflammatory response.
Barrier preparations are used to protect the skin by coating the surface of the skin and/or by supplying lipids that can penetrate the intercellular spaces of the stratum corneum. Effective products may contain barrier lipids, enzyme inhibitors, antimicrobial agents, inflammatory agents, and a physical barrier such as clay or zinc oxide to prevent undesirable microbes from binding to the skin; thereby, preventing dermatitis. However, the barrier should not be overhydrated through the addition of strong humectants because the skin’s barrier in both diaper dermatitis and elderly incontinence dermatitis is already overhydrated, which leads to rapid maceration.
Studies have shown that a good protocol of care can reduce the risk of pressure ulcers.9,10 This underscores the fact that barrier products are an important component of care for the prevention of pressure ulcers and skin breakdown.
The Food and Drug Administration’s “Skin Protectant Drug Products for Over-the-Counter Human Use: Final Monograph”11 includes a number of materials that can be claimed as skin protectants. Barrier products can be differentiated into two general types: one works by forming a film on the skin after evaporation of a solvent and the second, such as ointments and creams, forms a hydrophobic, physical barrier. A previous study12 evaluated film-forming skin protectant efficacy over a 1-week period. The purpose of this three-part study was to measure the barrier function and skin hydration potential of six marketed skin protectant products and to assess the efficacy of products that form a hydrophobic, physical barrier.
Materials and Methods
Study design and definitions. Within the description of the study, the terms hydration, barrier effect, and barrier function are used. Hydration refers to the water content present at the stratum corneum. Barrier effect relates to the physical properties of the products in preventing irritants or moisture from coming in contact with the skin. Barrier function refers to the natural barrier properties of the stratum corneum, specifically in relation to how products aid in its maintenance and repair.
In order to fully assess each of the barrier products, the study was split into three phases. Phase 1 investigated the barrier effect of each test product by applying a known irritant via an occlusive patch on top of the product applied to the skin. Resulting erythema was subsequently assessed. Phase 2 investigated the hydration and barrier function of the skin using a Corneometer® (Courage and Khazaka, Köln, Germany) and measured transepidermal water loss (TEWL). Transepidermal water loss is the normal, constitutive loss of water vapor from the skin in the absence of sweat gland activity and is an indicator of skin barrier function. It can be measured at baseline and after the application of topical treatments. Phase 3 investigated the product barrier effect using a dye retention technique and included chromameter measurements.
Selection of healthy volunteers. Each of the phases of the study involved the participation of at least 15 healthy persons. Healthy volunteers in the Hill-Top Research (UK) database were contacted via telephone and invited to participate in the study; 18 were recruited to ensure at least 15 volunteers completed each study phase. Sixteen volunteers completed phase 1, 15 volunteers completed phase 2, and 17 volunteers completed phase 3. All phases of the study were conducted at Hill-Top Research, Manchester, UK. [Editor’s note: Hill-Top Research (UK) is now 4Front Research; Hill-Top data are maintained at its Cincinnati, Ohio facility.]
Screening. Fifty-four healthy volunteers were recruited into the study to allow for a minimum of 45 healthy volunteers to enter the active phase — a minimum of 15 volunteers for each part of the study. Healthy volunteers had to meet inclusion/exclusion criteria (see Table 1), were prepared to accept the protocol-directed prohibitions and restrictions (see Table 2), and provided written informed consent.
Subject eligibility was confirmed using a study-specific pre-treatment questionnaire or a copy of the oral screener from the subject database Study Participant Access Network (SPAN).
Materials. The products tested in this study are listed in Table 3. White soft petrolatum (Penreco, Karns City, Pa.) was used as a positive control for barrier properties, glycerin (Kramer Chemicals, Clifton, NJ) served as a positive control for skin hydration, and methylene blue dye (Sigma, Dorset, UK) was used to dye the skin during barrier studies.
Equipment.
Chromameter CR200 (Minolta, Milton Keynes, UK). The chromameter illuminates the skin surface using a pulsed xenon arc lamp. The light was reflected perpendicular to the surface and data were collected for a tristimulus color analysis at 450 nm, 560 nm, and 600 nm using the L*a*b* color system.12 The skin area studied measured 8 mm in diameter (0.50 cm2). Each chromameter reading taken for skin color determination is the mean of three measurements. To keep the pressure of the measurement probe from influencing the color measurement of the skin, a 4-cm diameter ring was attached to the probe, resulting in an applied pressure of 52 g/cm2. Before readings were taken, the instrument was calibrated using a standard white plate. This instrument has been used to assess the blanching effect of corticosteroids and has been found to be more objective than visual assessment.13
Corneometer® MPA5 (Courage and Khazaka, Köln, Germany). Data from this instrument are based on capacitance measurement of a dielectric medium. Any change in the dielectric constant due to skin surface hydration variation alters the capacitance of a precision measuring capacitor.
Tewameter® MPA5 (Courage & Khazaka, Köln, Germany). The measurement of water evaporation is based on the diffusion principle in an open chamber. The density gradient was measured indirectly by the two pairs of sensors (temperature and relative humidity) inside the hollow cylinder and analyzed by a microprocessor.
Procedure.
Phase 1: Barrier effectiveness against irritants. Patches consisting of 5-cm wide strips of occlusive BlendermTM tape (3M, St. Paul, Minn.) to which Webril® disks (Tyco Health Care/Kendall, Mansfield, Mass.), approximately 2.5 cm in diameter, were fixed along the midline of the occlusive tape. The skin of the volar forearm was marked with dots of crystal violet applied on either side of the top disk and below the bottom disk of each strip to denote the exact location of subsequent patches. Each subject was asked to avoid the dye marks during washing and to keep the patches dry. When patch adhesion reinforcement was necessary, strips of porous Scanpore® tape (Norgesplaster A/S, Norway) were applied.
Seven test sites of approximately 12 cm2 were marked on the subjects’ upper arms — five sites were treated with the test products (0.010 mL/cm2 (10µL/cm2), one site served as a positive control (white petrolatum), and the remaining site served as a negative control (untreated). Products were left on the skin for 15 to 20 minutes before the application of the SLS challenge patch. Patches containing 0.40 mL of 0.3% SLS in water were then placed over all seven test sites for 24 hours. After the patches were removed, the test sites were assessed and a fresh SLS patch was re-applied for another 24 hours. The product application sequence for each subject was documented and maintained throughout the study using a color-coded identification card.
Subjects were instructed to keep the patches dry and in place for the two 24-hour periods. After each test period, the subjects returned to the center for re-application or assessment. Patches were applied on days 1 and 2 and assessment of patch sites was carried out before application of the second 24-hour patch and then 24, 48, and 72 hours after final patch removal.
A trained scorer assessed all patch sites on all days using appropriate lighting to illuminate the areas. All assessments were completed according to the scoring scale where 0 represents no apparent cutaneous involvement and 4 represents generalized vesicles, eschar formations, moderate-to-severe erythema, and/or edema extending beyond the area of the patch (see Table 4).
Phase 2: Transepidermal water loss and skin hydration. Subjects were given a bland soap product (Simple® Soap, Accantia, Solihull, UK) to use on their legs for the 3 days preceding the active part of the study. All subjects (men and women) were instructed to shave their legs 3 days before the start of the study and not to shave their legs for the duration of the study. All volunteers were instructed not to use any other treatment products (eg, moisturizing foam baths, shower gels or soaps, lotions and creams, and depilatory products) on their lower legs for the following 5 days.
Volunteers were acclimatized by remaining seated for at least 30 minutes in a controlled environment (temperature 22° C ± 2° C, relative humidity 45% ± 5%). During the rest period, one lower leg was marked with eight areas, each approximately 12 cm2. Before product application, the test sites were wiped with a dry, soft tissue. A single measurement was recorded at each site using the probe attachment of the Tewameter®. Three readings were taken at each site using the probe attachment of the Corneometer®. Between each assessment, the probe attachment was pressed onto a dry tissue.
Each of the test products and the positive control were applied to one of the eight 12-cm2 areas (0.010 mL/cm2 or 10µL/cm2) according to a randomization schedule. One site on each leg remained untreated. Sites were assessed with both the Tewameter® and Corneometer® probes at baseline and 1, 2, 4, and 6 hours following application of the test products. Between-treatment analysis was performed for each of the test products, comparing them with the untreated site at each time point. Within-treatment analysis was performed to determine if significant changes had occurred from baseline to each of the other time points.
Phase 3: Chromameter barrier analysis. Before the start of phase 3, subjects rested for at least 30 minutes in a controlled environment (temperature 22°C ± 2°C , relative humidity of 45% ± 5%). During the rest period, the left volar forearm of each volunteer was marked with seven double circles (4 cm in diameter), each containing a smaller 1.5-cm diameter, centrally located circle. Before product application, the test sites were wiped with a dry, soft tissue. A single color measurement using the L*a*b* system was recorded at each site on the arm with a Chromameter®.
Digital photographs of the test sites were taken adjacent to the instrument readings. Methylene blue dye was applied to the left forearm in the innermost circles of each site using a dye stamp. The sites were left to dry for 30 minutes before baseline Chromameter® readings of the dyed skin were obtained.
The test products were applied to one of the five areas on both arms (0.010 mL/cm2) using a cotted finger and rubbed in for 60 seconds. The positive control (white petrolatum) was applied to the sixth site and the remaining site remained untreated. The test articles were applied in accordance with the protocol’s randomization schedule and all sites were left exposed to the air for an additional 30 minutes.
A single initial measurement was recorded at each site on the left arm 30 minutes after test article application and air exposure using the Chromameter®. Subjects then were asked to submerge all test sites in a water bath set at 32° C for 10 minutes, after which arms were blotted dry using a towelette. A final set of colorimetric readings was taken.
Data analysis.
All data were acquired and analyzed and are now maintained by Hill-Top Research (US).
Phase 1. Following grading (see Table 4) by a trained scorer, the mean irritancy grading score for all volunteers at each time point and for each product was calculated and compared using a two-sample significance test.
Phase 2. After recording the TEWL and conductance measurements, the mean for both measurements between all volunteers at each time point and for each product was calculated and compared using ANOVA techniques followed by multiple comparisons utilizing Dunnett’s test.
Phase 3. Between-treatment analysis was performed for each of the test articles, comparing them with the control site at each time point. Within-treatment analysis was performed to determine color changes from baseline for all time points. Data analysis was calculated and compared using a two-sample significance test.
Chromameter® assessments of skin color (L*a*b*system). Using a spreadsheet, the color difference between the skin color, product application, and color after washing can be calculated using the following equation:
ΔEab = √[(ΔL*)2 + (Δa*)2 + (Δb*)2]
Where ΔL = difference in L Light – Dark
Δa = difference in a Green – Red
Δb = difference in b Blue – Yellow
Results
All testing was carried out independently by Hill-Top Research, including all statistical analyses. Hill-Top has all raw data on file; for the purpose of this report, in most cases only ANOVA data are provided.
Phase 1: Barrier effectiveness against irritants. The most effective barriers were those that contained zinc oxide, followed by water-in-oil and non-aqueous based formulations. The least effective barrier product to the insult was the oil-in-water based formulation. Specifically, for Product D, a highest grading of 1.50 was observed on day 3, with a lowest grading of 0.53 on day 2 (see Figure 1). Comparison of the mean scores indicated statistically significant differences in irritation grading compared to theuntreated site for Products A (0.031), B (0.000), C (0.594), and E (0.000) for day 2. Significant differences in irritation grading compared to the untreated site also were recorded on day 3 for Products C (0.594) and E (0.281) (see Table 5 for P values).
Phase 2: TEWL and skin hydration. Over a 6-hour period, the glycerin-treated site was significantly improved (P <0.0001, 95% confidence level) compared to the untreated site, supporting the ability of glycerin to hydrate the skin. For up to 4 hours, the oil-in-water and non-aqueous based product (Products B and D) sites were significantly better than the untreated sites, owing to their ability to moisturize the skin (P <0.0001). The petrolatum and water-in-oil based product (Product A) increased skin hydration for up to 1 hour. The products containing zinc oxide (Products C and E), irrespective of their base formulation, were comparable to the untreated site over 6 hours (see Figures 2 and 3 and Tables 6 and 7).
Phase 3. When left on the skin for Phase 3, a number of products appeared to be more efficacious when compared to the data generated for TEWL in Phase 2 when the products were removed from the skin. Both Product A and petrolatum demonstrated significant increases in barrier function (P <0.005 each) compared to the untreated site within Phase 3. Within Phase 2, however, barrier function was not significant compared to the untreated site. This is due to product removal required for Phase 2 before measurements were taken. Data indicate that emulsion type and water affinity may play a role in a product’s ability to maintain a barrier function against maceration. The water-in-oil emulsion type (Product A) effectively maintained 80% of the dye on the skin, compared to the oil-in-water emulsion type (Product F), which did not exhibit any increased effectiveness compared to the untreated site (39% dye retention on the skin) (see Figure 4 and Table 8).
Discussion
The purpose of this study was to assess the barrier and skin hydration properties of currently available skin protectants used in the care of patients with incontinence. The primary purpose of these products is to protect the skin from breakdown due to moisture and irritants from urinary and fecal incontinence while maintaining a natural moisture balance. Because skin protectants are applied to at-risk or compromised skin, both the skin hydration and skin barrier protection properties of these products are important.
Phases 1 and 2 of the study examined how the products modify the properties of the stratum corneum. All measurements were taken after the products were removed to assess the manner in which the products perform either by absorption into the skin or by providing an occlusive barrier on the skin surface. Further investigations that examine these properties while the product remains on the skin surface would provide a greater knowledge of performance in vivo.
Phase 1. Phase 1 of the study assessed the barrier properties of the products against a known irritant, SLS. It was observed that skin damage increased in response to the insult up to day 4, followed by skin improvement at day 5. Two products (A and D) showed an improvement in skin condition between days 3 and 4 (see Figure 1).
Although the positive control (petrolatum) is known to be an effective skin barrier, evidence of erythema in this case suggested that the control may enhance the penetration of some substances (such as drugs and the surfactant SLS) due to its lipophilic occlusive property. This is more pronounced under occlusive patches. In such cases a surfactant, under a patch, can “emulsify” the petrolatum — it resides on the surface of the skin and within the upper layers of the stratum corneum and will penetrate deeper within the skin barrier at a slow rate. Enhanced penetration of emulsified SLS-petrolatum also occurs because of patch occlusion14; thus, increasing the rate of irritation responses.14,15 However, the other emulsion-based products tested in this study that were likely to have penetrated the skin at a faster rate than the petrolatum enabled a “within” stratum corneum barrier to be formed (less product on the skin surface), reducing the effect of the applied SLS within that same time frame. More research is required to support this hypothesis. Lanolin (present in some of the products tested) has a chemical composition that closely mimics some of the natural skin barrier stratum corneum lipid components and has excellent barrier properties and repair function. It has been shown more effective than petrolatum in barrier function recovery and protection against barrier insult.16
Within a good protocol of care aimed at protecting the patient with incontinence from skin breakdown, skin protectants are removed from the skin during cleansing after each incontinence episode. The skin protectant is then re-applied. In the clinical setting, skin protectants are removed and re-applied at least once within every 24 hours. Therefore, for phase 1 testing, it was appropriate to evaluate the results after 24 hours, which may be deemed a worst-case scenario. At 24 hours, sites of four test products exhibited no signs of irritation (Products A [P = 0.006], B [P = 0.005], C [P = 0.005], and E [P = 0.005]). The remaining three test product sites (Product D and petrolatum and untreated area) exhibited signs of slight erythema and/or dryness.
Phase 2. Phase 2 assessed skin hydration potential and TEWL following product application. In this phase, all measurements were taken after the products were removed to allow each product to be assessed on its ability to repair the skin’s natural barrier. For both skin hydration and TEWL measurements, the time from initial application of the products to the first measurement was 1 hour.
An advantage of the capacitance measurement method, compared to other methods, is that products applied to the skin only have minimal influence on the result obtained. The capacitance instrument is able to detect even slight changes in the hydration level of the skin.
Different skin hydration profiles were obtained for each of the test products (see Figure 2). Glycerin, the positive control, is a humectant, a substance that binds to water and incorporates into products to promote retention of moisture. Both Product D, which contains glycerin, and Product B, which contains propylene glycol (which may be considered a humectant), are shown to hydrate the skin. Petrolatum hydrates the skin by creating an occlusive barrier over the stratum corneum, preventing water loss and hydrating the skin from within. Product A may work in a similar manner due to its high petrolatum content. The decrease in hydration following 1-hour application is due to the removal of the product, allowing the trapped moisture to escape via TEWL.
The two products containing zinc oxide (Products C and E) exhibited no skin hydration potential. Product C is an oil-in-water based formulation containing petrolatum. Although this product may be expected to act in a similar way to petrolatum, zinc oxide particulates within the formulation may attract the moisture away from the skin but not sufficiently to dry the skin. Product E is an ointment-based product; in this product, zinc oxide particulates within the formulation may disrupt the occlusive nature of the formulation, limiting skin hydration potential. However, this product showed a small increase in hydration at 1 hour, suggesting that if the product were allowed to remain on the skin surface, hydration measurements may have increased. Further study is required to support this observation.
Products A and E and petrolatum (see Figure 3) all showed increases in TEWL at 1 hour, probably due to the build up of moisture within the skin (see Figure 2). After 2, 4, and 6 hours, no statistical difference was noted between these products and the untreated test site — most likely because the amount of product left on the skin was minimal. These results suggest that a minimal amount of product is absorbed into the stratum corneum within 1 hour and that these products influence TEWL by forming a physical occlusive barrier on the surface of the skin.
No statistical difference was found at the 95% confidence level in TEWL between Product D and the untreated site. Product D offers good skin hydration, indicating that the product is absorbed to some extent into the skin but does not affect TEWL.
Product C, which contains zinc oxide, showed a difference in TEWL compared to the untreated site at 4 and 6 hours. This suggests that some product is absorbed into the skin before excess is removed from the stratum corneum surface at 1 hour. However, the product offers minimal skin hydration, suggesting that although an occlusive barrier is formed, the zinc oxide particulates within the formulation may have adsorbed any available moisture. Glycerin and Product B both showed a reduction in TEWL up to 6 hours.
Phase 3. A good barrier product will prevent a water-soluble dye from being removed from the skin by water. The positive control, petrolatum, was the most effective at maintaining a barrier following water immersion, indicated by 80% retention of the dye in the skin. The petrolatum-containing Product A performed in a similar manner (78% retention, P = 0.715) when compared to petrolatum site. Product C, which also contained petrolatum, was not as effective in preventing dye removal (46% of color retained). This may be related to the concentration of petrolatum or the possible disruptive effect of particulate zinc oxide contained in the formulation. Products B, F, and D (which retained 17%, 39%, and 41% of the dye, respectively), which have dimethicone as the primary barrier, were shown to be less effective in preventing dye removal from the skin. A statistically significant difference was noted between Product B and the untreated test site (P = 0.001, 95% confidence level). The reason for this is as yet unclear, but may be related to product interaction with the dye. No statistical difference was reported between the untreated test site and Products C, D, and F; however, a statistical difference was noted between the untreated area and Products C, D, and F compared to Product A (P <0.005) and the petrolatum control test products.
Overall. Over the 5-day period, the two zinc oxide-based products demonstrated greater efficacy at preventing irritant insult to the skin compared to the other products. Up to day 2, the irritancy grading was zero for these products. The protective barrier effects of zinc oxide on the skin have been previously reported.17,18 The non-aqueous and petrolatum-containing water-in-oil products showed significant barrier properties compared to the untreated sites. After 2 days, the irritancy grading was less than 0.1, in contrast to a grading of 0.6 for the untreated site. In this study, the oil-in-water dimethicone product exhibited no barrier function to SLS insult compared to the untreated site. This finding needs to be further investigated because evidence to suggest that dimethicone-containing lotions have a protective effect for up to 48 hours is limited.19
Glycerin, the positive control, showed greatest efficacy for skin hydration. The oil-in-water dimethicone product containing a humectant also demonstrated good skin hydration potential over 6 hours. Petrolatum-based products showed skin hydration properties over a short time period, while zinc oxide-based products showed minimal hydration of the skin. The TEWL analysis demonstrated the products’ ability to improve or maintain the skin’s natural defense system. All products showed no detrimental effect to the skin natural barrier function at 2, 4, and 6 hours.
It can be concluded that if these products were rubbed off the skin surface during use, Products A, E, B, and C would still offer some protection against irritant insult. Products A, B, and D would offer skin hydration. All study products would maintain the skin’s natural defense against maceration but with no significant modification of the TEWL.
When the product was left on the skin for Phase 3, a number of products appeared to be more efficacious when compared to the data generated for TEWL in Phase 2 when the products were removed from the skin. This suggests that these products work primarily by forming an occlusive layer on the surface of the skin to support skin barrier repair, promote skin hydration, and ultimately establish a physical barrier.
The ability to prevent the water-soluble dye from washing off the skin indicates effective barrier function. The chromameter results suggest that the petrolatum-based products have increased barrier function compared to the dimethicone-based products.
Some evidence was noted of the dye being taken up during the application of water-based products. Although the methodology attempts to compensate for this fact, it appears to differentiate between products that are based on water-in-oil emulsions compared with those that are water-based. However, the results suggest that petrolatum-containing barrier products are more efficacious than dimethicone-based products in protecting skin from insult or maceration.
Conclusion
Each of the products tested offers different skin hydration and skin protection potential (see Table 9). The water-in-oil products containing petrolatum are more efficacious than the oil-in-water products containing dimethicone in protecting the skin from insult or maceration. The dimethicone-containing products, however, offer higher hydration properties compared to the petrolatum-containing products, which in some of the products tested may be due to the higher level of available water. Zinc oxide products protect against irritants most effectively.
Overall, the water-in-oil petrolatum-based product was the only test article shown to be efficacious within all parameters tested — ie, a barrier to irritants, with skin hydration potential and a barrier against maceration.
This study suggests that skin barrier protection involves more than just the inclusion of an “active” barrier ingredient. Clearly, the influence of the emulsion structure and formulation are important for barrier protection. However, achieving a balance to protect against all the elements that may threaten the skin integrity of a patient with incontinence — ie, protecting and hydrating the skin and prevent- ing maceration — is equally important.
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