P1.14 Penetration of titanium dioxide microparticles into follicular orifice

J. Lademann, N. Otberg, H. Richter, U. Jacobi, U. Blume-Peytavi, H. Schaefer, W. Sterry

Center of Experimental and Applied Cutaneous Physiology, Department of Dermatology and Allergology, Charité - Universitätsmedizin, Berlin, Germany

Coated titanium dioxide microparticles are commonly used as a UV filter substance in commercial sunscreen products. The penetration of coated titanium dioxide microparticles into the stratum corneum and into hair follicles was investigated in vivo by tape stripping and biopsies in combination with spectroscopic measurements. Small amounts of microparticles were found in deeper parts of the stratum corneum after long-term application of a sunscreen containing titanium dioxide. These small amounts were clearly located in the follicle orifices while the surrounding corneocytes were free of TiO₂ in these parts of the horny layer. The biopsy sections were analyzed by X-ray fluorescence measurements using an ESM 2000 electron microscope (Carl Zeiss Germany), and a TN5525 X-ray spectrometer (Tracor Northern). The electron microscope was used to reveal the structure of the biopsy section and to position the electron measuring spot for X-ray excitation to the site of a follicular orifice. The analysis of biopsy sections containing hair follicle channels showed that small amounts of TiO₂ microparticles penetrated into the acroinfundibulum of follicles without reaching the viable cells. Microparticles were only found in 1 out of 10 hair follicles. „Active“ and „inactive” hair follicles could be distinguished in relation to their penetration characteristics.