Study of the influence of alcohol on the photostability of four UV filters

OBJECTIVE

Spray formulations are currently under development in the field of topical photoprotection. Such forms are characterized by their high fluidity, a property that is obtained by the presence of alcohol in the formula. The purpose of this work was to study the influence of ethanol in sunscreens on the photoprotective efficacy as well as the photostability of UV filters.

MATERIALS AND METHODS

The filters tested were octyl methoxycinnamate (OMC), PEG-25 PABA, octyl salicylate and butyl methoxydibenzoylmethane (BMDBM) at their maximum concentration authorized by European regulations and in the presence of increasing amounts of alcohol, up to 15% (w/w).

RESULTS

The effect of the presence of alcohol on the efficacy of the filters and their photostability varies depending on the molecule considered. Alcohol has no effect on octyl salicylate, either on its efficacy or its photostability. However, filter stabilization is seen for BMDBM and PEG-25 PABA.

CONCLUSIONS

Although these differences are significant, they are not great enough to justify large-scale use of ethanol in sunscreen products due to some of its properties, such as flammability.

Study of the influence of substrate and spectrophotometer characteristics on the in vitro measurement of sunscreens efficiency

All the methods used for the in vitro measurement of the SPF, the universal indicator of sunscreens efficiency, rely on a spectrophotometric analysis. What can vary about the experimental protocol used is mainly the substrate and the type of spectrophotometer chosen. We decided to work with polymethylmetacrylate plates that we analyzed using two spectrophotometers equipped with integrating spheres, the UV1000S and the UV2000 apparatus. Two marketed products were such tested, after spreading 2 mg/cm² on the plates, using one apparatus after another. We applied a non-parametric Wilcoxon test for paired data to the measures realized on 10 plates (as we systematically used the 2 apparatus), in order to compare the series of measures obtained with the two machines. This way, we were able to show a significant difference between the SPF values respectively obtained with the UV1000S and the UV2000 spectrophotometers. This difference could be explained by the decrease of the stray light in the case of the UV2000 apparatus.

Comparison of two in vitro methods to evaluate the water resistance of sunscreens

For a long time, the water resistance of sunscreens has been determined in vivo, according to Colipa's (Comité de Liaison des Industries de la Parfumerie) procedure. This method is not so ethical as healthy volunteers are irradiated, and can be replaced by an in vitro method which is easy and quick to perform. The objective of this work was to correlate the experimental device proposed by Choquenet et al. and the dissolutest (Sotax AT6). This equipment is used in the pharmaceutical industry to control the tablets. The experimental conditions have been fixed to correlate the results obtained with both methods. The stirring speed for the dissolutest was fixed at 75 rpm, which is the speed value recommended by the European Pharmacopeia to study the dissolution over time of tablets.

Interest of external photoprotection by means of clothing and sunscreen products in young children

BACKGROUND

Protecting young children is a major public health issue.

OBJECTIVE

We tested children's clothing and sunscreen products that are specially designed for children.

METHODS

The effectiveness of the different types of clothing and sunscreen products was determined using spectrophotometer equipped with an integrating sphere A measure of transmittance carried out, respectively, between 290 and 400 nm and between 320 and 400 nm, allowed us to assess the photoprotective properties in the UVB and UVA range respectively.

RESULTS

Although the photoprotective effect varies according to the type of clothing (UV-protection factor [UPF] of approximately 10 for a cotton T-shirt and 500 for a pair of jeans), the effect is constant for any one type of clothing. Placing fabrics in layers is essential and this enables the protective effect to be greatly increased. Moreover, the authors wished to answer the question, 'what makes a good sun cream?' by analysing the formula of each product tested. It turns out that only creams containing both organic filters and inorganic filters have an sun protection factor (SPF) that is the same as the one stated on the product.

CONCLUSION

Concerning townwear, the jeans, tracksuits, sweatshirts, pullovers and tights turned out to be very photoprotective. They enable, in effect, to reach a UPF higher than 500. The mere presence of titanium dioxide and/or zinc dioxide does not mean that the product will have a high SPF. Products containing alcohol can be eliminated from the possible choices by carefully reading the label.

Adaptation of the protocol for determining in vitro the sun protection factor of anti-solar sticks

Apart from the protection offered by clothing, the application of sunscreen products suited to each type of skin constitutes one way for decreasing the frequency of skin cancers nowadays. After having adapted an in vitro method for determining the efficacy of sunscreens in emulsion form, we wished to transpose this technique by adapting it for the anti-solar sticks for the evaluation of sun protection factor (SPF) using a spectrophotometer equipped with an integrating sphere. To do this, we tested 14 products in the market as well as sticks that we ourselves fabricated in the laboratory. In a base common to all of these sticks, we added organic (13 filters tested) and inorganic (two filters tested, titanium dioxide and zinc oxide) to their maximum permitted concentration in the European Union. In parallel, emulsions containing the same filters at the same percentage of use were studied; to be in keeping with the results on the products packaging on the one hand, and with the results obtained for the emulsion form on the other hand, we were able to determine the optimal mass which needed to be placed on the support used the in vitro test to determine the SPF.

Development of an in vitro test to determine the water-resistance of sunscreens

The aim of this work was to develop an in vitro method for testing the water resistance of sun products. For comparison, we used the in vivo method put forward by the Colipa. Standards and commercial products were successive baths. The Sun protection factor of these different creams was determined in vitro both before and after the baths. The result was that two successive baths of 20 min in moderately shaken distilled water, at 29 +/- 2 degrees C and may substitute the in vivo test.

Mineral filters in sunscreen products--comparison of the efficacy of zinc oxide and titanium dioxide by in vitro method

European legislation currently authorizes 26 sun filters among which, there is only one mineral filter: titanium dioxide. In the United States, two mineral filters are authorized: titanium dioxide in a maximum dose of 25% and zinc oxide. Zinc oxide is authorized in Europe, but its concentration level is not limited. A large number of commercial products are containing one of these mineral filters. The difference between these products lies in the percentage of the active substance, the way they are incorporated into the final product and the size of the primary particles. Depending on the ingredient used, there is a large variation in efficacy. The efficacy of the products tested was determined by an in vitro method using a spectrophotometer equipped with an integration sphere. Titanium dioxide was thus seen to be much more effective than zinc oxide; indeed no commercial form of zinc oxide tested can give a sun protection factor (SPF) higher than 10 at its maximum dose of use, unlike titanium dioxide which in its coated form (coated with alumina and with stearic acid, amongst others) gives a SPF of 38. This study has also allowed us to dispel the theory that talc--a raw material which has been used empirically for years in foundation in the belief that it has photoprotective effects--has an effect against sun rays. Talc proved to be particularly ineffective, as when it is used at a level of 25%, it only gives a totally negligible SPF of one unit.

Effect of the combination of organic and inorganic filters on the Sun Protection Factor (SPF) determined by in vitro method

This paper describes the effect on Sun Protection Factor (SPF) of the combination of inorganic and organic filters in sunscreen products as determined by an in vitro method. O/W emulsions containing inorganic filters, such as titanium dioxide and zinc oxide, combined with 18 EU-authorized UV-B organic filters were tested. SPF measurements were carried out using a spectrophotometer equipped with an integrating sphere. This study observed a synergic effect when titanium dioxide was combined with either anisotriazine or octyldimethylPABA. The combination of zinc oxide with 11 UV-B organic filters also exhibited a similar synergy; however, the measured SPF was systematically lower than the protection factor achieved with titanium dioxide.

Study of the efficacy of 18 sun filters authorized in European Union tested in vitro

In this work, the authors study the influence of filter concentration on the SPF in a topical product measured in vitro. Firstly, the method was adapted by determining that a mass of 15 mg of product must be applied on the PMMA (polymethylmethacrylate) plate in order to have the best correlation with results obtained in vivo. By using the highest concentration allowed by European legislation, the following ranking was drawn up in ascending order of efficacy: 3-Benzylidene camphor (1.66) < oxybenzone (3.01) < octylsalicylate (3.12) < PABA (3.36) < polysilicone 15 (3.64) < methylene bis-benzotriazolyl tetramethylbutylphenol (3.68) < PEG25 PABA (3.81) < benzophenone-4 (3.85) < 4-methylbenzylidene camphor (4.22) < homosalate (4.33) < octyltriazone (7.80) < phenylbenzimidazole sulfonic acid (8.31) < octyldimethyl PABA (8.71) < octocrylene (10.41) < octylmethoxycinnamate (10.42) < diethylhexylbutamidotriazone (12.58) <isoamylparamethoxycinnamate (15.14) < anisotriazine (20.0).