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Notes: In order to help clarify the controversially discussed dermal uptake properties of micronized titanium dioxide (TiO 〈inlineGraphic alt="inline image" href="urn:x-wiley:01425463:ICS211924:ICS_211924_mu1" location="equation/ICS_211924_mu1.gif" extraInfo="missing"/〉), we conducted extensive in vitro dermal absorption studies with ’Franz-type’ diffusion cells on excised porcine skin. After biopsies and chemical fixation, the overall localization of TiO 〈inlineGraphic alt="inline image" href="urn:x-wiley:01425463:ICS211924:ICS_211924_mu2" location="equation/ICS_211924_mu2.gif" extraInfo="missing"/〉 in the skin was analyzed by means of transmission electron microscopy (TEM). The lateral and vertical distribution of TiO 〈inlineGraphic alt="inline image" href="urn:x-wiley:01425463:ICS211924:ICS_211924_mu3" location="equation/ICS_211924_mu3.gif" extraInfo="missing"/〉 within the stratum corneum (SC) was investigated by tape stripping and subsequent scanning electron microscopy (SEM) in combination with energy dispersive X-ray analysis (EDXA).TiO 〈inlineGraphic alt="inline image" href="urn:x-wiley:01425463:ICS211924:ICS_211924_mu4" location="equation/ICS_211924_mu4.gif" extraInfo="missing"/〉 was found exclusively on the outermost SC layer. The surface deposit, as displayed by TEM, featured clearly distinguishable agglomerates as well as single particles with a characteristic cubic shape and a primary particle size of about 20–50 nm. Concurrently, SEM/EDXA micrographs first showed an even distribution of TiO 〈inlineGraphic alt="inline image" href="urn:x-wiley:01425463:ICS211924:ICS_211924_mu5" location="equation/ICS_211924_mu5.gif" extraInfo="missing"/〉 on the skin surface. After 10-fold stripping, however, TiO 〈inlineGraphic alt="inline image" href="urn:x-wiley:01425463:ICS211924:ICS_211924_mu6" location="equation/ICS_211924_mu6.gif" extraInfo="missing"/〉 was found to be localized only in the furrows and not on the partially removed ridges of the skin surface. SEM/EDXA micrographs of the adhesive tape strips revealed a characteristic pattern of stripped material and free regions. This pattern was an imprint of the skin’s topography. Hence, tape stripping initially removed TiO 〈inlineGraphic alt="inline image" href="urn:x-wiley:01425463:ICS211924:ICS_211924_mu7" location="equation/ICS_211924_mu7.gif" extraInfo="missing"/〉 and SC layers only from the ridges and not from the deeper furrows. Continued stripping increasingly yielded material from the deeper contours of the SC surface. TiO 〈inlineGraphic alt="inline image" href="urn:x-wiley:01425463:ICS211924:ICS_211924_mu8" location="equation/ICS_211924_mu8.gif" extraInfo="missing"/〉 was found only in traces in the upper part of the follicle without any evidence of uptake into the follicular epithelium. This indicates that there is not any relevant penetration via the follicular route.We conclude that due to the microtopography of the skin, the strip number normally does not reflect the SC layer number. Accordingly, tape stripping results should always be interpreted with care, especially in the case of topically applied particles, as even higher numbers of subsequent strips may still sample material from the outermost SC layer of the deeper furrows, which could be interpreted falsely as penetrated material. Our results clearly demonstrate that TiO 〈inlineGraphic alt="inline image" href="urn:x-wiley:01425463:ICS211924:ICS_211924_mu9" location="equation/ICS_211924_mu9.gif" extraInfo="missing"/〉 homogeneously and completely covers the outermost SC layer. It is neither delivered to the SC nor to the underlying skin layers when applied topically to porcine skin in vitro in the cosmetic vehicle used here. These findings underscore the safety of this micronized inorganic UV filter.