The H2O2-mediated oxidation of zero-valent silver nanoparticles (AgNPs) under acidic conditions (pHs 3.0, 3.5 and 4.0) is investigated here as is the associated production of hydroxyl radicals (HO center dot). Citrate-stabilized AgNPs initially react with H2O2 to form reactive intermediates with these species subsequently (i) reacting with an additional molecule of H2O2 to form surface-associated Ag(I) and O-2(center dot-) with subsequent reduction of a portion of the Ag(I) species to Ag-0 via electron charging-discharging processes, and (ii) decomposing with the aid of protons to produce HO center dot. The combined generation of HO center dot and release of Ag+ from AgNPs under acidic conditions may synergistically affect the viability of cells and tissues. As such, the safety of topical exposure to AgNP-containing commercial products which can access skin or internal organs such as the stomach warrants further investigation with regard to the impact of HO center dot generated by the AgNP-mediated decomposition of H2O2. (C) 2014 Elsevier Inc. All rights reserved.