Search

Photodegradation of 2.6 x 10(-5) M aqueous solutions of sodium usnate at various pH was studied. Photodegradation appeared to follow first-order kinetics and was found to be pH dependent. The degradation rate constant was calculated to be 9.20 x 10(-4) min-1, 5.93 x 10(-4) min-1, 9.69 x 10(-4) min-1, and 9.88 x 10(-4) min-1 at pH 6, pH 7, pH 8, and pH 9, respectively.

The authors quantified the abrasiveness of toothpastes found on the market by using a profilometric technique. This technique is based on the study of the surface state of polymethacrylate plates submitted to a brushing simulation. The study of the profiles obtained experimentaly allowed determination of two values: one (A) that gives the total quantity eroded and one (a) that gives the quality, which means the regularity of this abrasion. Depending on the values of A and a obtained, it is possible to classify the toothpastes as: very slightly abrasive, slightly abrasive, abrasive, and very abrasive.

The use of sunscreens with sun protective cloths is the photoprotection way mostly used by Occidentals. During sweating or a bath, those products should be still efficient. As the emulsion is the mostly used type of product format, it is essential that the scientist knows how to formulate an emulsion which will be water resistant. The HLB (hydrophilic-lipophilic balance) of a formulation has high influence on this characteristic.

Water is the most important molecule contained in the skin and is bound to the intracellular hygroscopic substances called natural moisturizing factors (NMF). The clinical characteristic of xerosis is rough and/or coarse skin. This anaesthetic alteration necessitates cosmetic products application. In this study, we tested the efficiency of urea incorporated into six different emulsions (O/W) and 10 different gels. Skin of 10 healthy women (20 to 45 years) was treated using 50 mg of emulsion or gel containing 5% of urea. A skin surface of 16 cm(2) was chosen in the area of the forearm. The gain in moisturizing was performed measuring the skin electrical capacity using a corneometer (Courage & Khazaka, model CM 825), one hour after treatment. Sodium carboxymethyl cellulose gel has the least moisturizing effect. On the other hand, the mixture of polyacrylamide and C13-14 isoparaffin polysorbate 85 can be a good vehicle in the treatment of skin dehydration. Adding various oils (6%) or collagen in aqueous solution does not improve the efficiency of the tested products. Moisturizing effect of gels (polyacrylamine with C13-14 isoparaffin polysorbate 85) is higher than the one of emulsions (L/H).