Broad spectrum bioactive sunscreens

It is well established that sun exposure is the main cause for the development of skin cancer. Chronic continuous UV radiation is believed to induce malignant melanoma, whereas intermittent high-dose UV exposure contributes to the occurrence of actinic keratosis as precursor lesions of squamous cell carcinoma as well as basal cell carcinoma. Not only photocarcinogenesis but also the mechanisms of photoaging have recently become apparent. In this respect the use of sunscreens seemed to prove to be more and more important and popular within the last decades. However, there is still inconsistency about the usefulness of sunscreens. Several studies show that inadequate use and incomplete UV spectrum efficacy may compromise protection more than previously expected. The sunscreen market is crowded by numerous products. Inorganic sunscreens such as zinc oxide and titanium oxide have a wide spectral range of activity compared to most of the organic sunscreen products. It is not uncommon for organic sunscreens to cause photocontact allergy, but their cosmetic acceptability is still superior to the one given by inorganic sunscreens. Recently, modern galenic approaches such as micronization and encapsulation allow the development of high-quality inorganic sunscreens. The potential systemic toxicity of organic sunscreens has lately primarily been discussed controversially in public, and several studies show contradictory results. Although a matter of debate, at present the sun protection factor (SPF) is the most reliable information for the consumer as a measure of sunscreen filter efficacy. In this context additional tests have been introduced for the evaluation of not only the protective effect against erythema but also protection against UV-induced immunological and mutational effects. Recently, combinations of UV filters with agents active in DNA repair have been introduced in order to improve photoprotection. This article reviews the efficacy of sunscreens in the prevention of epithelial and nonepithelial skin cancer, the effect on immunosuppression and the value of the SPF as well as new developments on the sunscreen market.

/pdf/sunscreens-which-and-what-for-23673wyfsk.pdf

Sunscreens - which and what for?

The UVA-attenuating properties of the three UVA filters butyl methoxy dibenzoyl methane (BMDBM), methylene bis-benzotriazolyl tetramethylbutylphenol (MBBT), and microfine zinc oxide (ZnO), are compared. For this purpose persistent pigment darkening (PPD) as an in vivo method as well as different in vitro approaches like the UVA/UVB ratio, the critical wavelength, and the Australian standard have been used. For the case of the UVA/UVB ratio and the critical wavelength the behaviour was also assessed after irradiation with 10 minimal erythemal doses (MED). Sunscreen formulations were manufactured containing either one of these UVA filters or combinations of one UVA filter and a constant amount of UVB filter. The concentration of the respective UVA filter was varied. BMDBM was dissolved in the oil phase of the formulations. MBBT, which is produced as particulate organic UVA-filter dispersion with average particle size smaller than 200 nm, was added to the aqueous phase. The microfine ZnO was incorporated into the oil phase. If no additional UVB filters were present, UVA/UVB ratio and critical wavelength stayed almost constant, independent of UVA-filter content. With constant levels of additional UVB filters these parameters increased with UVA-filter concentration. In contrast to the behaviour of the UVA/UVB ratio, which appeared to be a sensitive measure for the UVA protection in relation to UVB protection in almost the whole ranges of UVA-filter concentrations, the critical wavelength approached saturation already at low UVA-filter levels. The UVA-protection factors (UVA-PF) obtained from the in vivo studies increased with the concentration of the UVA filter in the formulations. Formulations, which showed UVA-PFs > or = 4 in most cases met also the conditions of the Australian Standard. An irradiation dose of 2.5 kJ m(-2) (10 MED) induced significant decreases of UVA/UVB ratio or critical wavelength only with some BMDBM formulations, indicating a loss of UVA protection in those cases.

In vivo and in vitro assessment of UVA protection by sunscreen formulations containing either butyl methoxy dibenzoyl methane, methylene bis-benzotriazolyl tetramethylbutylphenol, or microfine ZnO

An extensive study on the sun protection factors (SPF) of sun care products was carried out using the COLIPA (The European Cosmetic Toiletry and Perfumery Association) method, which relates to in vivo experiments. Furthermore, in vitro methods were tested with sunscreen formulations that were prepared as films on surface-roughened plates of polymethyl methacrylate (PMMA). One of the in vitro methods, i.e. using the sunscreen tester, has been recently developed, whereas the second has been defined by a pure spectroscopic approach, which is based on spectral transmission measurements of sunscreen films. Altogether 58 different sunscreen formulations, with manufacturer declared SPF values ranging from 4 to 60 and currently available on the European market, were investigated. The quality of correlations with results from the individual products based on the different in vitro methods versus the COLIPA values that were considered as generally accepted standard values was assessed. In this context, also variations because of sample preparation and spectral measurement were discussed. For sunscreen products with in vivo SPF values larger 25, the spectral transmittance within the UVA/UVB range is rapidly decreasing, which is experienced even for products with reduced amounts reaching 0.5 mg cm(-2) and still leading to unsatisfactory correlation of the spectroscopically derived SPF values versus the results from the alternative assays. Opposite to these small amounts, a sunscreen product spread of 2 mg cm(-2) is standard for the in vivo COLIPA method, whereas an area-normalized amount of 1 mg cm(-2) is currently routinely used for the sunscreen tester method. Furthermore, an overview of the individual product characteristics, such as their specific critical wavelengths and their UVA/UVB ratios is provided; both parameters can also be calculated from the spectral absorbances of the standardized sunscreen films.

Comparison of sun protection factors determined by an in vivo and different in vitro methodologies: a study with 58 different commercially available sunscreen products.

In the past, several attempts have been made to develop in vitro methods for determining protection against UV radiation. To date however, there is no broadly accepted method. Various known and unknown parameters influence the transmission measurements of scattering films, such as the multifaceted compositions of sunscreens, the technical limitations of measurement devices as well as the difficulty to apply very thin films of sunscreen in a reproducible manner throughout different laboratories. In vitro data were measured in this multicenter study to compare possible methodologies and strategies for an in vitro approach to the sun protection factor (SPF). This publication will not present a final in vitro SPF test method, but it will point out which technical side effects may influence such a method. Influential factors such as the quality of spectrophotometer used, the amount of product applied, pretreatment of samples, time and temperature of equilibration, size of the measured surface, the application process or the calculation on the basis of standardized data are presented and discussed. Finally, a reduction of the standard deviations within single laboratories could be realized for in vitro SPF testing, but no improvement of the interlaboratory comparison was obtained. The development of a valid and reliable SPF in vitro test still remains a challenge, and further work is necessary to develop a satisfactory method.

In vitro Sun Protection Factor: Still a Challenge with No Final Answer

The UVA protection delivered by sunscreens is an issue of increasing importance due to the increasing knowledge about UVA-induced skin damage. In Europe there is no officially accepted method available to determine the degree of UVA protection. Therefore, the objective of the present study was to design a protocol combining the merits of an in vitro model, which are simple and reproducible, with aspects known to be relevant from in vivo studies. The principle is: an UV-transparent support to which the test product is applied, a (pre)irradiation and a transmission measurement. Transpore(R) tape (standard support for SPF determinations) was found to be incompatible with many preparations on prolonged contact times. Roughened quartz was adopted as a suitable alternative. Transmission measurements on this support are not reliable with a layer of 2 mg cm(-2) (standard for SPF) due to detection limitations of spectrophotometers, hence a reduced layer of 0.75 mg cm(-2) was adopted. Overall, it is very difficult to apply products in a reproducible thin layer on appropriate substrates. As a consequence, absolute parameters derived from the transmission profile show relatively large dispersion, whereas relative parameters, such as critical wavelength lambda(c)[1] or UVA/UVB ratio are much less sensitive to unavoidable variations in layer thickness. An increase in deviations was observed when the samples were irradiated before measurement. It is crucial to control the output carefully (spectral distribution and even more importantly, irradiance and dose delivered) of the light source. By doing so and also taking into account the previous learning steps, a protocol was drafted and tested in a ringtest (four samples in six laboratories). The results are encouraging and show that if relative parameters (e.g. lambda(c), UVA/UVB ratio) are considered, the intra- as well as interlaboratory reproducibility is clearly better than can be obtained in vivo. In general, we describe a suitable method, which can be considered in any future official discussions about the methodology to determine UVA protection.

In vitro testing to assess the UVA protection performance of sun care products.

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In vitro testing to assess the UVA protection performance of sun care products.