Solid lipid nanoparticles (SLN)--a novel carrier for UV blockers.

The formulation of safe sunscreen products is of high importance due to their increasing use because of the diminishing ozone layer. Solid lipid nanoparticles (SLN) are introduced as the new generation of carriers for cosmetics, especially for UV blockers for the use on human skin and/or hair and production thereof is described. The crystalline cetylpalmitate SLN particles have the ability of reflecting and scattering UV radiation on their own thus leading to photoprotection without the need for molecular sunscreens. An in vitro assay showed that a placebo cetyl palmitate SLN formulation is twice to three times as potent in absorbing UV radiation as a conventional emulsion. Incorporation of sunscreens into SLN lead to a synergistic photoprotection, i.e. higher than the additive effect of UV scattering caused by the SLN and UV absorption by the sunscreen. The photoprotective effect after incorporation of the molecular sunscreen 2-hydroxy-4-methoxybenzophenone (Eusolex 4360) into the SLN dispersion was observed to be increased threefold compared to a reference emulsion. Further, film formation on the skin was investigated by scanning electron microscopy, showing particle fusion due to water evaporation and formation of a dense film.