Effect of topically applied lipids on surfactant-irritated skin

New innovation of moisturizers containing non-steroidal anti-inflammatory agents for atopic dermatitis

Atopic dermatitis is a chronic, relapsing and extremely pruritic eczematous disease which commonly affects children. The standard management consists of a combination of anti-inflammatory drugs in adjunctive with skin care management particular moisturizer application. A concern for the side effects associated with long term use of corticosteroids has also been considered. There has been an emerging interest in moisturizer containing non-steroidal anti-inflammatory agents such as herbal extracts, vitamins, mineral and lipids. The in vitro and the in vivo studies of each agent were reviewed. The clinical study on the efficacy of moisturizers containing these agents were also demonstrated including the author’s studies and clinical experience. These moisturizers might be considered as an alternative treatment in acute flare of mild to moderate atopic dermatitis.

Do moisturizers work?

Moisturizers are used on large body surfaces to maintain the smoothness of the skin and to break the dry-skin cycle. Many healthcare professionals and patients overlook the importance of moisturizers and do not consider them to be 'active' treatments. However, evidence from clinical and experimental studies shows that moisturizers enhance both the smoothness and hydration of skin. Different moisturizers have different ingredients, and each may have a different mode of action. Some smooth the skin, others affect barrier function. Some enhance barrier function in both diseased and normal skin. Others impair barrier function in both diseased and normal skin. Defective barrier function may trigger the development of eczema. The composition of a particular moisturizer should reflect its desired therapeutic effect, i.e. a moisturizer to diminish dryness may need different ingredients from those required to improve barrier function. The content of excipients, such as emulsifiers, chelating agents and antioxidants, may have greater impact than is commonly believed. Greater tailoring of moisturizers will improve their efficacy. Confidence in the therapeutic effects of moisturizers will be enhanced by well-designed randomized controlled trials.

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.

The hairless guinea-pig as a model for treatment of acute irritation in humans

BACKGROUND

The effect of six skin care formulations on experimentally induced acute irritation was studied in hairless guinea-pigs (HLGP) and in human volunteers (HV). The formulations were a basic cream, a carbomer cream and four modifications of the carbomer cream, containing either 10% isopropyl palmitate (IPP cream), 10% glycerol (glycerol cream), 19.5% canola oil (canola oil cream) or 0.5% (-)-alpha-bisabolol (bisabolol cream).

METHODS

Acute irritation was induced by occlusive tests with 1% sodium lauryl sulfate aq. in both HLGP and HV, and in HV also by using nonanoic acid in n-propanol (NON) 20%. The irritant reactions were treated twice daily with the formulations from the time of removal of the patches. Evaluation of skin irritation and efficacy of treatments was performed daily for 4 days using clinical scoring, evaporimetry (transepidermal water loss), hydration measurement and colorimetry.

RESULTS

The glycerol cream was the only product showing effects potentially better than no treatment in HV.

CONCLUSION

The HLGP was too sensitive an animal model as a predictor for effect in humans. There was no difference in efficacy of the formulations against the two different irritants in HV.

Transepidermal water loss reflects permeability barrier status: validation in human and rodent in vivo and ex vivo models

Permeability barrier function is measured with instruments that assess transepidermal water loss (TEWL), either with closed- or open-loop systems. Yet, the validity of TEWL as a measure of barrier status has been questioned recently. Hence, we tested the validity of this measure by comparing TEWL across a wide range of perturbations, with a variety of methods, and in a variety of models. TEWL rates with two closed-chamber systems (VapoMeter and H4300) and one closed-loop system (MEECO) under different experimental in vivo conditions were compared with data from four open-loop instruments, i.e. TM 210, TM 300, DermaLab and EP 1. The instruments were compared in vivo both in humans and hairless mice skin subjected to different degrees of acute barrier disruption. The values obtained with bioengineering systems were correlated with absolute water loss rates, determined gravimetrically. Measurements with both closed and open systems correlated not only with each other, but each method detected different degrees of barrier dysfunction. Although all instruments differentiated among gradations in TEWL in the mid-range of barrier disruption in vivo, differences in very low and very high levels of disruption were less accurately measured with the H4300 and DermaLab systems. Nevertheless, a high Pearson correlation coefficient (r) was calculated for data from all instruments vs. gravimetrically assessed TEWL. Together, these results verify the utility of TEWL as a measure of permeability barrier status. Moreover, all tested instruments are reliable tools for the assessment of variations in permeability barrier function.

The hairless guinea-pig as a model for treatment of cumulative irritation in humans

BACKGROUND

The effect of six skin-care formulations (SCFs) on experimentally induced cumulative irritation was studied in hairless guinea-pigs (HLGPs) and in human volunteers (HVs). The formulations were a basic cream, a carbomer cream and four modifications of the carbomer cream, containing either 10% isopropyl palmitate (IPP cream), 10% glycerol (glycerol cream), 19.5% canola oil (canola oil cream) or 0.5% (-)-alpha-bisabolol (bisabolol cream).

METHODS

In HLGP, irritant dermatitis was induced with 30 min daily exposure for 4 days to 0.5% sodium lauryl sulfate aq. (SLS). In HVs, irritant dermatitis was induced with 10 min daily exposure for 5+4 days (no irritation on weekends) to 3% SLS aq. on the right and 30% nonanoic acid (NON) in n-propanol on the left volar forearm. Clinical scoring was performed daily; evaporimetry (total epidermal water loss (TEWL)), hydration and colorimetry were measured at baseline (day 0) in the middle and at the end of treatment. Treatments were applied twice daily. The basic cream and the IPP cream were excluded from testing in HLGP because they were known from previous studies to be irritant in HLGP, while all formulations were known to be equally and well tolerated locally in humans.

RESULTS

All formulations worsened the skin irritation in HLGP: the glycerol cream the least, the canola oil cream the most, while the bisabolol cream and the carbomer cream were indistinguishable. In humans, the glycerol cream was better than 'No Treatment' after cumulative irritation with both SLS and NON. The basic cream was better tolerated in humans than was expected from previous testing in HLGPs.

CONCLUSION

In conclusion, the results from the studies in HLGPs and HVs are in agreement with regard to ranking of the SCFs. Further, the glycerol cream showed a positive treatment effect on both SLS- and NON-irritated skin in HVs.

The clinical benefit of moisturizers

Moisturizing creams marketed to consumers often contain trendy ingredients and are accompanied by exciting names and attractive claims. Moisturizers are also an important part of the dermatologist's armamentarium to treat dry skin conditions and maintain healthy skin. The products can be regarded as cosmetics, but may also be regulated as medicinal products if they are marketed against dry skin diseases, such as atopic dermatitis and ichthyosis. When moisturizers are used on the so-called dry skin, many distinct disorders that manifest themselves with the generally recognized symptoms of dryness are treated. Dryness is not a single entity, but is characterized by differences in chemistry and morphology in the epidermis depending on the internal and external stressors of the skin. Patients and the society expect dermatologists and pharmacists to be able to recommend treatment for various dry skin conditions upon evidence-based medicine.

LEARNING OBJECTIVE

Upon completing this paper, the reader should be aware of different types of moisturizers and their major constituents. Furthermore, s/he will know more about the relief of dryness symptoms and the functional changes of the skin induced by moisturizers.

Comparison between 2 test models in evaluating the effect of a moisturizer on irritated human skin

The purpose of the present study was to compare 2 experimental models of moisturizer efficacy on the recovery of irritated skin on the hands and the volar forearms. 12 healthy volunteers had their hands immersed in sodium lauryl sulfate (SLS) 10 min 2x daily for 2 days, and at the same time the volunteers had patch tests with SLS (0.125%, 0.25% and 0.5%) applied on their forearms for 24 h. After irritation of the skin, the volunteers had a moisturizer applied on one arm/hand 3x daily for the following 9 days. The other arm/hand served as untreated control. Evaluation was done on days (D) 1, 3, 5, 8 and 12 by transepidermal water loss, electrical capacitance, laser Doppler flowmetry and DermaSpectrometry. Both models were found useful, and the moisturizer was found to accelerate regeneration of the skin barrier function in both the hands (D8, p<0.05) and the volar forearms (0.5% SLS, D5 and D8, p<0.01). When the forearm model is used in the present set-up, a relatively high concentration of SLS (>0.25%) should be used and evaluation measurements are best performed on D5-D8. The forearm model proved reliable and easy to handle and we suggest that this model is used in future studies on moisturizer evaluation.