On the Detection and Scope of "Third-Hand Vaping": A Critical Review of the Literature.

Background: "Third-hand" exposure produced by "second-hand" environmental vaping aerosol (EVA) has been reported as a parallel analogue of "third-hand smoke" (THS) produced by residues of environmental tobacco smoke (ETS). Methods: To assess the plausibility and scope of "third-hand" vaping exposure, we examine the available evidence on THS phenomenology and the physicochemical properties of EVA. We also evaluate daily intake doses from direct dermal exposure to nicotine under simplified but minimally realistic scenarios for vaping and smoking. Results: The only THS phenomenology fully reproduced in EVA is the adsorption of nicotine and its byproducts on indoor surfaces. Unlike significant, measurable THS exposures in normal environments (homes, hospitality venues, cars), third-hand exposures from vaping have only been found under special conditions: laboratory-generated aerosols or in vape shops where excessively abnormal and intense vaping activity takes place. Conclusions: The physicochemical properties of EVA are incompatible with an aging process leading to a THS analogue under the environmental conditions in which vaping normally takes place. However, objectively and rigorously evaluating the risks of dermal exposure from smoking and vaping remains an open issue.