Influence of climatic conditions on antiperspirant efficacy determined at different test areas.

BACKGROUND: The efficacy of antiperspirants is a current topic among the developers of cosmetic products. According to the Food and Drug Administration (FDA) for the US market, efficacy testing performed in the axilla of human volunteers is mandatory. Another method is yet available, which enables comparison of more than one antiperspirant formula in a single study by performing the test on the backs of volunteers. However, how reproducible are these methods, comparing between the back and axilla? Do they differ as a result of seasonal variation? Is a correlation between the results of the two methods possible? METHODS: To answer these questions, the antiperspirant efficacy of aluminium chlorohydrate (ACH) aqueous solutions was investigated in the axilla and on the backs of volunteers, in four separate clinical studies covering cold and warm seasons. Four days of product application were followed by thermal sweat induction on the fifth day, using a sauna. The amount of sweat recovered by weighing cotton pads before and after sweat induction was used to calculate sweat reduction. Testing in the axilla and on the back was performed on the same volunteers simultaneously to achieve the best comparable data. For this reason, the FDA guideline was slightly modified to thermal stimulation in a sauna instead of in a hot room. RESULTS: Increasing concentrations of ACH in aqueous solutions on the backs of volunteers showed a saturation for 8% ACH with a sweat reduction of approximately 50%. The antiperspirant efficacy of solutions containing 4%, 8% or 12% ACH was repeatedly found at the same levels, when tested on the backs during summer, autumn and winter time. Axilla tests, with an 8% ACH aqueous solution, showed strongly varying results for summer and winter time, represented by sweat reduction values of -2% to 25%. As an assumption, these high variations might result from reduced gel formation in cold seasons due to low humidity in the axillae during the application phase. On the back, this effect was avoided by applying occlusive foils after product application. To gain further insight, a study, during which summer conditions were artificially simulated by thermal stimulation during the application phase, again showed decreased antiperspirant efficacy in the axilla for winter conditions with sweat reduction values of 2%, compared with 25% under simulated summer conditions. CONCLUSION: These strongly varying values of sweat reduction in the axilla under summer and winter conditions make comparisons between antiperspirant products difficult and a statement about correlation between the two test sites back and axilla impossible. A standardization of the application phase, comparable to the simulated summer conditions described here, could be a solution to reduce the high variation of results in the axilla. Consequently, testing on the back is not only a more cost-effective method to investigate the antiperspirant efficacy of more than one formulation, but a reproducible method more independent of climatic influences during test implementation than the axilla test method. It could, therefore, be regarded as the method of choice for discriminating antiperspirant efficacy between several products during development of new antiperspirant formulations.

Non-invasive evaluation techniques to quantify the efficacy of cosmetic anti-cellulite products.

BACKGROUND: The majority of women suffer from the unattractive sight of dimpling skin on the thighs and buttocks, globally known as cellulite. Cellulite can be regarded as the most investigated non-disease, because, from the cosmetic viewpoint, most women desire a reduction in cellulite severity. Despite investigations made, cellulite is still not well understood at the cellular level, which leads to controversy regarding the investigative methods for cellulite reduction as well as the development of products to treat cellulite skin. OBJECTIVE: The aim of our work was to improve the set up of macrophotography for making images of dimpled skin and to automatize image analysis of 20 MHz ultrasound imaging - these two methods being just two of a variety of available methods for investigating cellulite skin. METHODS: Macrophotography was standardized on the aspects of volunteer's positioning, skin illumination, background used, and camera position. It was performed before, during and after a 3-month-treatment of a cosmetic product. Scoring assessments of the generated images were made by the volunteers themselves as well as by six trained experts. Ultrasound imaging was performed at the baseline visit in order to correlate the newly developed analysis with the visually rated cellulite score. A second study is also presented showing a variety of parameters that can be used for cosmetic testing of cellulite products: skin firmness, blood circulation and circumferential thigh measurements. RESULTS: Standardization of macrophotography minimized differences in image features between assessment times, therefore, enabling follow-up rating assessments of the images. A custom-made rating program simplified the scoring procedure by presenting images as blind and randomized, and by implementing computer-based analysis using an online rating scale. Volunteers and experts scored significant improvement of skin appearance over the course of a 3-month cosmetic treatment. Image analysis of ultrasound imaging was automatized, and a modification of the commonly known roughness parameter Ra was implemented to characterize cellulite severity. Comparison with the visually rated cellulite score showed an existing correlation between the score and the modified parameter Ra(m). Further parameters investigated in an exemplary study, as mentioned above, demonstrated a significant improvement of skin appearance after treatment with a cosmetic product. CONCLUSIONS: Macrophotography and ultrasound imaging can be regarded as important tools for determining and quantifying the aspects of cellulite. With a gold standard missing for investigating cellulite severity, these two methods may not determine cellulite at the cellular level, but they do characterize the skin appearance so typical for cellulite. Combined with a variety of other methods, macrophotography and ultrasound imaging can very well define cellulite-reducing efficacy from the cosmetic point of view.

Role of taurine accumulation in keratinocyte hydration.

Epidermal keratinocytes are exposed to a low water concentration at the stratum corneum-stratum granulosum interface. When epithelial tissues are osmotically perturbed, cellular protection and cell volume regulation is mediated by accumulation of organic osmolytes such as taurine. Previous studies reported the presence of taurine in the epidermis of several animal species. Therefore, we analyzed human skin for the presence of the taurine transporter (TAUT) and studied the accumulation of taurine as one potential mechanism protecting epidermal keratinocytes from dehydration. According to our results, TAUT is expressed as a 69 kDa protein in human epidermis but not in the dermis. For the epidermis a gradient was evident with maximal levels of TAUT in the outermost granular keratinocyte layer and lower levels in the stratum spinosum. No TAUT was found in the basal layer or in the stratum corneum. Keratinocyte accumulation of taurine was induced by experimental induction of skin dryness via application of silica gel to human skin. Cultured human keratinocytes accumulated taurine in a concentration- and osmolarity-dependent manner. TAUT mRNA levels were increased after exposure of human keratinocytes to hyperosmotic culture medium, indicating osmosensitive TAUT mRNA expression as part of the adaptation of keratinocytes to hyperosmotic stress. Keratinocyte uptake of taurine was inhibited by beta-alanine but not by other osmolytes such as betaine, inositol, or sorbitol. Accumulation of taurine protected cultured human keratinocytes from both osmotically induced and ultraviolet-induced apoptosis. Our data indicate that taurine is an important epidermal osmolyte required to maintain keratinocyte hydration in a dry environment.