Recently, Yanagisawa et al. reported that the transdermal exposure (mimicking skin-barrier dysfunction or defect) of NC/Nga mice to TiO₂ NPs (15, 50, or 100 nm), in combination with allergen, aggravated atopic dermatitis-like lesions through a T-helper type 2 (Th2) dominant immune response. The study also indicated that TiO₂ NPs can play a role in the initiation and/or progression of skin diseases, since histamine was released, even in the absence of allergen.