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Titanium dioxide nanoparticles (TiO2NPs) suspensions (concentration 1.0 g/L) in synthetic sweat solution were applied on Franz cells for 24 h using intact and needle-abraded human skin. Titanium content into skin and receiving phases was determined. Cytotoxicity (MTT, AlamarBlue® and propidium iodide, PI, uptake assays) was evaluated on HaCat keratinocytes after 24 h, 48 h, and seven days of exposure. After 24 h of exposure, no titanium was detectable in receiving solutions for both intact and damaged skin. Titanium was found in the epidermal layer after 24 h of exposure (0.47 ± 0.33 μg/cm2) while in the dermal layer, the concentration was below the limit of detection. Damaged skin, in its whole, has shown a similar concentration (0.53 ± 0.26 μg/cm2). Cytotoxicity studies on HaCaT cells demonstrated that TiO2NPs induced cytotoxic effects only at very high concentrations, reducing cell viability after seven days of exposure with EC50s of 8.8 × 10−4 M (MTT assay), 3.8 × 10−5 M (AlamarBlue® assay), and 7.6 × 10−4 M (PI uptake, index of a necrotic cell death). Our study demonstrated that TiO2NPs cannot permeate intact and damaged skin and can be found only in the stratum corneum and epidermis. Moreover, the low cytotoxic effect observed on human HaCaT keratinocytes suggests that these nano-compounds have a potential toxic effect at the skin level only after long-term exposure.

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Background: Hairdressers are at high risk of contact dermatitis (CD) due to skin exposure to numerous irritants and haptens in hair products in combination with frequent wet work. Objectives: To investigate the characteristics and incidence of CD among hairdressers in northeastern Italy. Methods: A total of 324 hairdressers who had been examined and patch tested in northeastern Italy from 1996 to 2016 were retrospectively identified, and compared with 9669 matched controls. Sensitization to allergens of the hairdressing series was analysed among hairdressers attending an occupational medicine clinic in Trieste, Italy. Incidence data were calculated from 1999 to 2016. Results: Sensitization to p-phenylenediamine, thiuram mix, and N-isopropyl-N'-phenylp-phenylenediamine was significantly associated with hairdressing and with hand/forearms dermatitis. Frequent sensitizers from hairdressing series were ammonium persulfate, toluene-2,5-diamine, and p-aminobenzene. The overall incidence of CD declined from 2003 (31.7 cases/10 000 workers) to 2016 (20.8 cases/10 000 workers). Conclusions: Sensitization to several haptens was significantly associated with hairdressing. The incidence of CD among hairdressers in northeastern Italy has declined in recent years, but is still high. Preventive efforts are needed to reduce the burden of CD in this professional group.

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