The skin of an adult person is, in most places, covered with a relatively thick (∼10 μm) barrier of keratinised dead cells. One of the main questions is still whether TiO2 NPs are able to penetrate into the deeper layers of the skin. The majority of studies suggest that TiO2 NPs, neither uncoated nor coated (SiO2, Al2O3 and SiO2/Al2O3) of different crystalline structures, penetrate normal animal or human skin. However, in most of these studies the exposures were short term (up to 48 h); only few long-term or repeated exposure studies have been published. Wu et al.83 have shown that dermal application of nano-TiO2 of different crystal structures and sizes (4–90 nm) to pig ears for 30 days did not result in penetration of NPs beyond deep epidermis. On the other hand, in the same study the authors reported dermal penetration of TiO2 NPs with subsequent appearance of lesions in multiple organs in hairless mice, that were dermal exposed to nano-TiO2 for 60 days. However, the relevance of this study for human exposure is not conclusive because hairless mice skin has abnormal hair follicles, and mice stratum corneum has higher lipid content than human stratum corneum, which may contribute to different penetration. Recently Sadrieh et al. performed a 4 week dermal exposure to three different TiO2 particles (uncoated submicron-sized, uncoated nano-sized and coated nano-sized) in 5 % sunscreen formulation with minipigs. They found elevated titanium levels in epidermis, dermis and in inguinal lymph nodes, but not in precapsular and submandibular lymph nodes and in liver. With the energy dispersive X-ray spectrometry and transmission electron microscopy (TEM) analysis the authors confirmed presence of few TiO2 particles in dermis and calculated that uncoated nano-sized TiO2 particles observed in dermis represented only 0.00008 % of the total applied amount of TiO2 particles. Based on the same assumptions used by the authors in their calculations it can be calculated that the total number of particles applied was 1.8 × 1013 /cm2 and of these 1.4 x107/cm2 penetrated. The surface area of skin in humans is around 1.8 m2 and for sun protection the cream is applied over whole body, which would mean that 4 week usage of such cream with 5 % TiO2 would result in penetration of totally 2.6 × 1010 particles. Although Sadrieh et al.concluded that there was no significant penetration of TiO2 NPs through intact normal epidermis, the results are not completely confirmative.
Titanium dioxide can be both safe and unsafe, depending on its use. When inhaled, titanium dioxide is considered possibly carcinogenic to humans. This means that in products that contain powdered titanium dioxide like loose powders, pressed powders, eyeshadows, and blushes in which the makeup is in powder form, titanium dioxide can be inhaled. Titanium dioxide is also an occupational chemical of concern, as workers might inhale titanium dioxide when manufacturing products.
2. The preparation of the lining powder: The above-mentioned final immersion liquid 1000 ml in a 2000 ml beaker, heated to 98 ° C, and then added 4 g of ammonium persulfate with a magnetic stirrer stirring 0. 5h, after the oxidation of the solution, adding polyacrylamide 02%。 The solution, the volume of the solution is 0.02%. After lh filtration, the obtained filtrate is subjected to sulfurization and impurity removal, and zinc powder is substituted to obtain a zinc sulfate ammonia refining complex liquid. 122. 9g of antimony sulfide (without water) and 21. 7g of sodium sulfide (without water) are mixed and dissolved in distilled water to obtain a metathesis reaction solution, and a nonionic surfactant 0P-10 (for nonylphenol and epoxy) is added to the solution. The condensate of acetamidine) 0. 2g, the reaction temperature is 40 ° C, the stirring speed is 15m / s, stir well for 40min, then slowly added to 1000ml zinc sulfate ammonia refining complex, continue to stir for 30min and then add quality The fractionation is 30% 3⁄40 2 of desulfurization bleaching, and after bleaching, the nZnS-BaS0 4 crystal filter cake is separated by filtration.