Penetration of titanium dioxide microparticles in a sunscreen formulation into the horny layer and the follicular orifice

Coated titanium dioxide (TiO2) microparticles are commonly used as UV filte r substances in commercial sunscreen products. The penetration of these mic roparticles into the horny layer and the orifice of the hairfollicle was in vestigated. The distribution of the microparticles in the horny layer was a nalyzed using the method of tape stripping in combination with spectroscopi c measurements. Deeper layers of the stratum corneum were devoid of TiO2 ev en after repetitive application of sunscreen preparation when analyzing int erfollicular areas. Only in the areas of the pilosebaceous orifices could m icroparticles be identified. The penetration of TiO2 was investigated in hi stological skin sections. A biopsy was taken from a skin area from which th e horny layer had been removed by tape stripping. In isolated areas, a pene tration of coated TiO2 into the open part of the follicle was observed. The amount of TiO2 found in a given follicle was less than 1% of the applied t otal amount of sunscreens. A penetration of microparticles into viable skin tissue could not be detected.