Opposing effects of glycerol on the protective function of the horny layer against irritants and on the penetration of hexyl nicotinate

Moisturizer therapy in prevention of atopic dermatitis and food allergy: To use or disuse?

OBJECTIVE

To critically appraise the evidence for the role of regular moisturizer application in early life to prevent atopic dermatitis (AD) and food allergy (FA).

DATA SOURCES

Primary peer-reviewed literature.

STUDY SELECTIONS

Original research articles based on systematic reviews, interventional studies, retrospective studies, case-control studies, and cohort studies related to the subject matter.

RESULTS

There is good evidence to show that epicutaneous sensitization through a defective skin barrier is important in the development of AD and FA. This supports moisturizer use in prevention because some of them have been proven to restore skin barrier with clear benefits in AD, whereas there is some limited evidence that these products may reduce allergic sensitization. However, moisturizers have varied effects depending on ingredients and formulation, some of which are paradoxical, such as increasing transepidermal water loss and enhancing penetration of substances in the skin. These effects may be responsible for some of the conflicting outcomes of prevention studies, some of which suggest that moisturizers are not useful in prevention of AD and FA, whereas others show a positive trend. Interestingly, there is some suggestion that moisturizers may increase the risk for allergy development perhaps through these paradoxical effects.

CONCLUSION

Although moisturizer use is beneficial in the management of AD, current evidence suggests that it may be ineffective in prevention of AD and FA. Further studies are needed to determine the effects of moisturization on allergic sensitization and inflammation and to investigate whether moisturizer type, frequency, duration, and age of application substantially affect the prevention and development of these allergies.

Enhancement of stratum corneum lipid structure improves skin barrier function and protects against irritation in adults with dry, eczema-prone, skin

BACKGROUND

The skin of atopic dermatitis (AD) patients is characterised by abnormal stratum corneum (SC) lipid levels. Consequently, the lamellar matrices are disrupted and skin barrier function is diminished, increasing skin sensitivity to irritants and allergens.

OBJECTIVE

To determine whether a cream containing ceramides, triglycerides and cholesterol in a multi-vesicular emulsion can reinforce the skin barrier, and protect against skin irritation.

METHODS

A randomized observer-blind intrasubject-controlled study in 34 adults with dry, eczema-prone, skin was conducted. Each participant underwent 4 weeks treatment with the test cream on one forearm and lower leg and a reference emollient cream on the other. Skin properties were determined before and after treatment. Lipid structure was assessed by FTIR spectroscopy using a novel interface.

RESULTS

Skin barrier integrity was greater at sites treated with the Test cream (effect size -161.9 area-under-the-TEWL-curve, 95% CI -205.5, -118.3), and skin sensitivity to sodium lauryl sulfate reduced (-0.5 points [97.57% CI -1.00, -0.25] visual redness and -15.34 g/m² /h [95% CI -20.28, -10.40] TEWL) compared to the reference. Sites treated with the test cream displayed enhanced lipid chain ordering, which was significantly associated with skin barrier integrity (r0.606). Compared to the reference, treatment with the Test cream increased hydration (8.61 capacitance units, 95% CI 6.61 to 10.60) and decreased signs of dryness.

CONCLUSION

The Test cream facilitates skin barrier restoration and protects the skin from dryness and irritation. Compared to a commonly prescribed emollient in the UK, the Test cream is highly suited to the management of dry, sensitive, skin.

Multi parametric biophysical assessment of treatment effects on xerotic skin

Background

Topical moisturizing products are widely used to alleviate the problems associated with xerotic skin. Their use affects many properties of the stratum corneum (SC) in a complex and interrelated manner. The range of measurement techniques available to the researcher has increased in recent years. However, few studies have looked for correlations between the different techniques for assessing how aspects of xerotic skin change over time as a result of topical moisturizer usage.

Objectives

A 3‐week in vivo study using an oil‐in‐water based moisturizing product and an untreated site was conducted to determine the clinical significance of and any correlations between a range of different approaches for the measurement of skin lipid content and also skin hydration and visual grading of dry skin.

Methods

A range of traditional and more recently developed skin measurement techniques have been used to examine a variety of SC properties in normal and xerotic skin during topical moisturizer usage.

Results

In vivo confocal Raman spectroscopy and analysis of SC lipids from tape strips both showed an increase in SC lipid level and organization after 3 weeks of moisturizer usage on xerotic skin. Hydration, measured both optically and electrically, also increased and skin barrier function improved, with strong correlations between the different measures of dryness being observed.

Conclusions

Strong correlations were observed between the skin measurements for lipid assessment and skin hydration with regard to the assessment of xerotic skin, providing valuable new information for future in vivo clinical research into dry and atopic skin.

Keywords

biophysical assessment, skin barrier, skin hydration, topical moisturizers, Xerosis

A high-emollient liquid cleanser for very dry and atopic-prone skin: Results of an in-use tolerance and efficacy study conducted under dermatological, pediatric, and ophthalmological supervision

BACKGROUND

Emollients play a key role in the treatment of eczematous lesions and xerosis such as in atopic dermatitis. However, studies that show the actual benefits of cleansers are few and far between.

AIMS

This study aims to evaluate the tolerance and efficacy of a high-emollient liquid cleanser (HELC) designed for very dry and atopic-prone skin, in the absence of any additional skin care. The product is a soap-free and fragrance-free liquid cleanser, containing mild surfactants and a ternary system of selected emollients: glycerin, vaseline, and paraffin.

METHODS

In-use study was conducted under dermatological, pediatric, and ophthalmological supervision in 50 subjects (infants, children, and adults) with "dry to very dry and atopic-prone" skin. The primary objective of this monocentric, open, and intra-individual study was to assess the dermatological and ophthalmological tolerance of HELC after 21 days of using it at least once a day on the face and body. The secondary objectives were to evaluate its efficacy based on a clinical score (SCORAD), assess its short- and long-term moisturizing effect by measuring hydration rates (Corneometer^® ), and ascertain its cosmetic acceptability through a subjective evaluation questionnaire.

RESULTS

The study validates the good dermatological and ophthalmological tolerance of HELC. Its efficacy was demonstrated by improvements in the SCORAD and moisturizing scores. Furthermore, the product was very well accepted by the subjects.

CONCLUSION

The fragrance-free HELC tested in this study for 21 days on "dry to very dry and atopic-prone skin" improves skin dryness and pruritus while ensuring good tolerance.

3-O-ethyl-l-ascorbic acid: Characterisation and investigation of single solvent systems for delivery to the skin

l-ascorbic acid (AA), commonly known as vitamin C, has been widely used in topical formulations for many years as an antioxidant and anti-aging ingredient. However, the physicochemical properties of AA are not optimal for skin uptake and the molecule is also unstable, readily undergoing oxidation on exposure to air. The compound 3-o-ethyl-l-ascorbic acid (EA) has been developed as a stable vitamin C derivative and has been used in topical products. The aims of this work were to conduct a comprehensive characterisation of physicochemical properties of EA as well as to investigate the influence of various neat solvents on EA skin delivery. Nuclear magnetic resonance (NMR), mass spectroscopy, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to characterise the molecule. The pK_a of the compound and the partition coefficient logP_(o/w) were experimentally determined. A new HPLC method for analysis of the molecule was also developed and validated. A number of solvents for topical preparations were selected based on their wide use as excipients in topical formulations, their potential to act as skin penetration enhancers and their favourable safety profiles. The solubility and stability of EA was examined. Skin permeation of the molecule in full thickness porcine skin in vitro was investigated using Franz-type diffusion cells. The melting point, log P_(o/w) value and pK_a value of EA were determined to be 114.39 ± 0.5 °C, −1.07 ± 0.03 and 7.72 ± 0.01 respectively. Skin penetration of EA was evident for the following vehicles 1,2 hexanediol (HEX), glycerol (GLY), propylene glycol (PG), 1,2 pentanediol (1-2P), isopropyl alcohol (IPA), propylene glycol monolaurate (PGML) and propylene glycol monocaprylate (PGMC). Skin uptake but no permeation through the skin was observed for Transcutol® (TC) and dipropylene glycol (DiPG), while no penetration was observed for the solvents 1,5 pentanediol (1-5P) and tripropylene glycol (TriPG). The findings of the permeation experiments confirm the potential of simple formulations to deliver EA to the skin. Studies are ongoing to identify complex vehicles for synergistic enhancement of EA skin penetration. To our knowledge this is the first study to conduct a comprehensive characterization of EA and examine its skin uptake and permeation properties in porcine skin.

Association of glycerol and paraffin in the treatment of ichthyosis in children: an international, multicentric, randomized, controlled, double-blind study

BACKGROUND

Efficacy and tolerance should be considered in topical treatments of chronicle affections with impaired skin barrier function such as ichthyosis.

OBJECTIVES

To demonstrate the efficacy of Dexeryl in reducing severity of ichthyosis.

METHODS

A prospective, multicentre, randomized, placebo controlled study was performed with patients under 18 years suffering from a non-bullous form of ichthyosis. A double-blind period using Dexeryl (an emollient cream containing glycerol 15% and paraffin 10%) or placebo (its vehicle) during 4 weeks followed by an open label period with all patients treated by Dexeryl for 8 weeks. Improvement of ichthyosis was assessed by cutaneous xerosis evolution (SRRC score): the percentage of patients with 50% reduction of the SRRC score at D28 was the primary criterion. The assessment of pruritus [visual analogue scale (VAS)], global evaluation and safety were secondary.

RESULTS

The percentage of patients with at least 50% reduction of SRRC score at D28 was significantly higher in Dexeryl group (60.3%) vs. vehicle group (43.5%; P = 0.008). Reduction of pruritus on VAS was significantly higher at D28 with Dexeryl (-2.16) compared to that in placebo (-1.49), P < 0.05. The improvement continues through the open label period: at D84 we observed -2.5 of SRRC score in the Dexeryl group vs.-1.8 for the group previously treated by vehicle. Investigators found Dexeryl efficacy as satisfying for about 80% of treated patients vs. 50% with vehicle. Concerning safety, most of the adverse events were not related to treatment.

CONCLUSIONS

Dexeryl showed a significant improvement of xerosis and related symptoms in children with ichthyosis and was well tolerated.

Measuring the effects of topical moisturizers on changes in stratum corneum thickness, water gradients and hydration in vivo

BACKGROUND

Moisturizers are the most commonly used topically applied product for the treatment of dry skin conditions. They affect many properties and functions of the stratum corneum but some moisturizers have been reported to be detrimental to barrier function. Stratum corneum barrier function is a composite of its total structure and thickness but few studies have taken this into account. As a biosensor, the stratum corneum (SC) will change its structure in response to treatment and a swelling effect has been clearly demonstrated by skin hydration. Recently several moisturizing agents have been shown to have an effect on SC swelling behaviour with conflicting results. However, there is a paucity of data reported for measuring the effects of long-term usage of moisturizers on SC thickness in vivo as, until recently, traditional techniques did not have the resolution to measure the effects of moisturizers on nonpalmoplantar body sites. The development of confocal Raman spectroscopy for use in human subjects provides noninvasive, real-time, in vivo measurement of SC water concentration profiles and we have also used this state of the art equipment to measure the effect of the long-term use of moisturizers on SC thickness for the first time.

OBJECTIVES

To validate the use of confocal Raman spectroscopy (CRS) to measure SC thickness and then use it to investigate the short- and long-term effects of moisturizers (one of which is known to improve SC barrier function) on SC thickness, water gradients and hydration.

METHODS

Two studies were conducted: (i) to validate the use of CRS for measuring SC thickness through comparison with optical coherence tomography (OCT); and (ii) once validated to use CRS to measure the long-term effects of three commercially available moisturizers (A, B, C) on SC thickness and water gradients, together with total hydration, over a 3-week period (2 weeks of treatment and 1 week regression) and compare the spectroscopy-derived hydration value with instrumentally derived capacitance hydration values.

RESULTS

(i) A strong, positive correlation in SC thickness was obtained between CRS and OCT (OCT-derived thickness = 0.96 x CRS-derived thickness, r(2) = 0.93; P <0.0001). OCT was shown, however, to have a lower resolution than CRS in distinguishing SC thickness on thinner nonpalmoplantar body sites. Using the CRS method, differences in SC thickness were readily apparent on different body sites (cheek 12.8 +/- 0.9 microm, volar forearm 18.0 +/- 3.9 microm, leg 22.0 +/- 6.9 microm). (ii) Examining the effects of moisturizers in a blinded, randomized 3-week study in human volunteers (n = 14) demonstrated that only one commercially available formulation (A) changed SC water gradients, thickness and hydration as measured by CRS. These hydration data did not directly correlate with capacitance hydration values.

CONCLUSIONS

(i) In vivo CRS was validated as a technique to measure SC thickness on both palmoplantar and, particularly, on nonpalmoplantar skin sites. (ii) Moisturizers improve skin moisturization but in this study only formulation A improved SC thickness, water gradients and hydration as measured by CRS. We hypothesize that this was due to compositional differences between the products. We believe that niacinamide (nicotinamide, vitamin B(3)) is probably contributing significantly to this effect, as it has been proven to increase epidermal lipogenesis and SC barrier function in other studies. These results show that by using CRS, we were able for the first time to determine the effect of moisturizer on multiple SC barrier endpoints including SC thickness, and water content as a function of depth and total SC water content.

Glycerol and the skin: holistic approach to its origin and functions

Glycerol is a trihydroxy alcohol that has been included for many years in topical dermatological preparations. In addition, endogenous glycerol plays a role in skin hydration, cutaneous elasticity and epidermal barrier repair. The aquaporin-3 transport channel and lipid metabolism in the pilosebaceous unit have been evidenced as potential pathways for endogenous delivery of glycerol and for its metabolism in the skin. Multiple effects of glycerol on the skin have been reported. The diverse actions of the polyol glycerol on the epidermis include improvement of stratum corneum hydration, skin barrier function and skin mechanical properties, inhibition of the stratum corneum lipid phase transition, protection against irritating stimuli, enhancement of desmosomal degradation, and acceleration of wound-healing processes. Even an antimicrobial effect has been demonstrated. Topical application of glycerol-containing products improves skin properties in diseases characterized by xerosis and impaired epidermal barrier function, such as atopic dermatitis. The increase of epidermal hydration by glycerol is critical in skin conditions aggravated by dry and cold environmental conditions, e.g. winter xerosis. This paper provides a review on effects of glycerol on the skin, the mechanisms of its action, and the potential applications of glycerol in dermatology.

Assessment of topical corticosteroid activity using the vasoconstriction assay in healthy volunteers

OBJECTIVE AND DESIGN

The aim of the study was to evaluate the vasoconstrictive activity of four new galenic preparations of hydrocortisone and to compare it with concentration-equivalent reference preparations. The study comprised two study phases: the pilot study phase and the main study phase. During open, nonrandomized pilot study, the optimal administration period was tested. The main study was performed in a randomized, double-blind intraindividual comparative design.

SUBJECTS

Twenty male and female volunteers with healthy skin who responded to topically applied clobetasol-17-propionate before entering the trial participated in this study.

TREATMENT

All subjects received the same treatments. The test preparations new galenic formulation (NGF) hydrocortisone 0.25% cream, NGF hydrocortisone acetate 0.25% cream, NGF hydrocortisone 0.5% cream, and NGF hydrocortisone 1.0% cream were compared with the respective reference preparations Soventol hydrocortisone (hydrocortisone acetate 0.25%), Hydroderm HC 0.5% cream (hydrocortisone 0.5%), Hydrogalen cream (hydrocortisone 1.0%) and placebo (vehicle of test preparations).

METHOD

The topical preparations were applied occlusively for 2 h (pilot study) or 24 h (main study) on outlined areas (5 x 5 cm with a distance of 3 cm) of both forearms (4 areas for each). Assessment of vasoconstriction was performed before treatment, and 0.5, 4, 6 and 24 h after treatment (observation period) using a subjective rating scale (OLSEN vasoconstriction score) and measuring the colorimetric parameter a* (redness) by use of the Chroma-Meter (Minolta company, Ahrensburg, Germany).

RESULTS

A significant vasoconstriction (positive blanching effect) was measured by use of chromametry for test preparations hydrocortisone 0.25% cream, hydrocortisone 0.5% cream, hydrocortisone 1.0% cream and for the reference preparation Hydrogalen cream compared to placebo 30 min after the end of treatment. In contrast, the reference preparations Soventol hydrocortisone and Hydroderm HC 0.5% did not differ significantly from placebo 30 min after treatment. No statistically significant effect of all formulations was observed 4-24 h after treatment in comparison with placebo.

CONCLUSIONS

The vasoconstrictive efficacy of test preparations was mostly stronger than the concentration-equivalent reference preparations. This effect was achieved by use of new galenics of test preparations resulting in enhanced skin penetration and improved efficiency. No unwanted side effects were observed during the course of the study despite increased efficacy of the topically applied test preparations.

Anti-irritants I: dose–response in acute irritation

The term 'anti-irritant' (AI) was coined in 1965 by Goldemberg to describe a diverse group of topical product ingredients, which were able to reduce the irritation potential of other more irritating ingredients in the same product. 'AIs' are being added to cosmetic formulations in order, allegedly, to benefit tolerability of the products and allow claims such as 'soothing' and 'healing' ingredients. Limited documentation in favour of the efficacy of AIs is published. We studied the dose-related effect of 4 alleged AIs (nifedipine, (-)-alpha-bisabolol, canola oil and glycerol) on experimentally induced acute irritation in healthy volunteers. Each AI was used in 3 concentrations. Acute irritation was induced by occlusive tests with 1% sodium lauryl sulfate and 20% nonanoic acid in N-propanol. The irritant reactions were treated twice daily with AI-containing formulations from the time of removal of the patches. Evaluation of skin irritation and efficacy of treatments were performed daily for 4 days using clinical scoring, evaporimetry (transepidermal water loss), hydration measurement and colourimetry. Only glycerol showed dose-response and effects potentially better than no treatment. There was no significant effect and no difference between the three other AIs.

Transcutaneous penetration of toluene in rat skin a microdialysis study

Percutaneous absorption of lipophilic substances has major implications for therapeutical use or toxicological effects. We, therefore, using dermal microdialysis, measured local toluene concentrations and assessed the effects of duration of exposure, skin barrier disruption and the use of skin-care products. Three microdialysis membranes (3000 kDa) were inserted intradermally at a length of 2 cm in the abdominal skin of 82 anaesthetized male Wistar rats. They were perfused with albumin solution (5%) at 10 microl/min. A skin area of 1.5 x 0.6 cm above the membranes was exposed to toluene (100%, 200 microl) for 15 or 240 min. Dialysate was sampled at 20-min intervals. Using GC-FPD (gas charomotography flame photometric detector), it was analysed for toluene. In addition, the effects of tape stripping and pretreatment with topical products were assessed. In each of the 12 permutations of exposure time, pretreatments and tape stripping, five to eight animals were investigated. Maximum toluene concentrations were reached at 60 min after exposure (3.07 +/- 0.40 microg/ml, 15 min; 5.38 +/- 0.92 microg/ml, 240 min). In 15-min exposure experiments, dermal toluene concentrations decreased slowly to reach baseline values after 240 min. After 240-min exposure, a plateau of approximately 6 microg/ml was reached after 60 min. Neither tape stripping nor the pretreatment with barrier cream induced a significant change on dermal toluene concentrations. The slow kinetics of toluene penetration results in a steep concentration gradient in the skin with very-high local toluene concentrations and a delayed wash out, which might be relevant not only toxicologically, but also therapeutically.

How do dermatological vehicles influence the horny layer?

Emulsifying agents in aqueous solution lead to dehydration of the horny layer of the epidermis and damage to the barrier. This is only partly true if emulsifying agents are constituents of emulsions. Water-in-oil (W/O) emulsions cause an improvement in the hydration of the horny layer and barrier function. In the case of an additional effect of wash solutions, a partial or complete abolition of the drying out and barrier-damaging effect of the wash solution results. Oil-in-water (O/W) emulsions without glycerol have no effect on the moisture of the horny layer or indeed increase it, but they lead to considerable damage to the barrier and irritation. In wash tests, they do not induce any protective effect. With micro-emulsions this is still more the case and, moreover, they can also lead to exsiccation. As a result of the addition of glycerol, the barrier-damaging effect can be abolished. Also in stress tests with wash solutions, the damage to the horny layer is reduced by glycerol-containing O/W emulsions. Whereas the penetration-promoting effect of O/W emulsions without glycerol is best, only W/O emulsions or glycerol-containing O/W emulsions are suitable for atopic dermatitis. A hydrating effect on the stratum corneum was also found in a propylene glycol ointment.

[Effects of emulsions on the stratum corneum barrier and hydration]

The appearance of the skin depends greatly on the hydration of the stratum corneum which is regulated by water binding substances of the corneocytes and also by the quality of the stratum corneum lipids. Furthermore these lipids are responsible for the barrier function. In patients with atopic dermatitis, the water binding capacity and the barrier function of the stratum corneum are reduced even in clinically healthy skin areas. Emollients can damage the stratum corneum and lead to desiccation and a disturbance of the barrier. This effect is a result of an increased permeability of the barrier lipids and direct damage to the keratinocytes and corneocytes. The degree of damage of the barrier caused by emollients in dermatological vehicles has not been sufficiently investigated. As suggested by hypothetical considerations, such an effect is not expected and cannot be demonstrated in water-in-oil-emulsions. Oil-in-water-emulsions without glycerol as well as lipophilic and hydrophilic microemulsions do damage the barrier function. Both types of microemulsions additionally lead to a dehydration of the stratum corneum. The damaging effect of oil-in-water-emulsions can be reduced by the addition of glycerol and urea.

Modern skin cleansers

The course of development of skin cleansers has been one of continual improvement. Soap-based products, used since antiquity, offered improved cleansing over mechanical methods or water alone but could irritate and dry skin. Bars based on synthetic detergents that offer improved skin compatibility compared with soap have become available over the past several decades. Body washes have been growing in consumer popularity. Some of the first body washes introduced into the market offered a moisturization benefit in addition to mildness. Some second-generation body washes that are now on the market use even more sophisticated formulation schemes, such as coacervate technology, to deliver emulsified petrolatum to the skin during washing, providing mild cleansing and a significant dry skin improvement benefit. Consumer demand and the formulation possibilities provided by new product formats, new technologies, and new ingredients will undoubtedly lead to the delivery of even greater skin benefits in the future.

Effects of four detergents on the in-vitro barrier function of human skin

The key to promoting percutaneous penetration is to alter the properties of the dermal barrier function. Mechanisms for changing the barrier function vary. Thus, some enhancers induce reversible conformational changes, whereas others cause prolonged barrier disruption. Discrimination between the influences of detergents on the barrier function may enable the use of those detergents affecting the overall integrity of the skin the least. In an experimental setup using in-vitro static diffusion cells mounted with human skin, the effects of four extensively used detergents on dermal barrier function were evaluated. Three of the detergents (lutensol AP10, nonyl phenyl ethoxylate, ethanol) apparently enhance percutaneous penetration without compromising the overall integrity of the skin barrier. SLS, on the other hand, acts through a time-and-dose-dependent deterioration of the dermal barrier function. The present experimental approach allows discrimination between detergents that act through different mechanisms to enhance percutaneous penetration.