Kinetics of swelling-breakdown of a W/O/W multiple emulsion: possible mechanisms for the lipophilic surfactant effect.

The properties and behavior of a W/O/W multiple emulsion formulation were analyzed during a swelling-breakdown process. Various experimental analyses, such as granulometry, rheology and conductimetry were performed, as well as a micropipette aspiration method. The predominant role of the lipophilic surfactant during the swelling phase confirmed. Two different mechanism can be proposed. Both imply the migration of the lipophilic surfactant from one interface to another and probably take place successively. The lipophilic surfactant could diffuse from the first to the second interface, thus rigidifying the membrane, or from the oily phase to the first interface, resulting in delayed coalescence of the aqueous droplets during swelling.

New ex-vivo method for evaluating the photoprotective efficacy of sunscreens.

Synopsis The photoprotective efficacy of some topical sunscreens was determined ex-vivo by spectrophotometric assay using an irradiation monochromator and a diffuse reflectance sphere. Transmission scans were run from 400 to 290 nm through human epidermis samples before and after application of products and protection factors (PF) were calculated. The results are also expressed as the percentage of the radiation stopped by the products in each spectral range (UVB, short UVA and long UVA). All the formulations contained two chemical filters: butyl methoxy dibenzoyl methane and octyl methoxycinnamate in a range of concentrations. Estimates of the effectiveness of all products were higher than results in humans when calculated by this ex-vivo technique. Due to its high discriminant power, this method constitutes a useful tool in the formulation of sunscreens.

Sunscreens' photochemical behaviour: in vivo evaluation by the stripping method.

This study shows the influence of a water-in-oil emulsion and an oil-in-water emulsion on the photochemical behaviour of four sunscreen preparations containing various amounts of three UV filters: octyl methoxycinnamate, butyl methoxydibenzoylmethane, and 4-methylbenzylidene camphor. With the stripping method in vivo, skin-product interactions were evaluated after topical application and ultra-violet exposure. Evaluations were also made under the same operating conditions as in determining sun protection factor in vivo. Results showed that each sunscreen preparation has a particular photochemical behaviour related to filter mixture and emulsion type. When developing a sunscreen preparation the choice of the emulsion type and filters is relevant for achieving optimum efficacy and spectral stability.