Introduction: Third-hand e-vaping refers to the residues left behind by vaping, which include nicotine and other chemicals. While e-vaping can adversely affect cognitive functions, research is limited on the effects of third-hand impacts, which formed the aim of this study.

Objective: To measure the changes in short-term memory and anxiety-like behaviours, as well as changes in cell numbers in the hippocampus.

Methods and Results: Balb/c mice (4 weeks, male) were exposed to freshly prepared towels daily for 4 weeks. Towels for the sham group were autoclaved only, while towels for the third-hand e-vaping groups were exposed to e-vapours with (18mg group) or without (0mg group) nicotine for 2 hours before being placed in the mouse cages. Mice exposed to the nicotine-free towels presented reduced short-term memory function during the Novel Objective Recognition Test, and those in the 18mg group spent the least time in the open arm of the elevated plus maze, suggesting increased anxiety. GFAP staining was increased in the cornu ammonis (CA)1, CA2, CA3, and dentate gyrus regions of the hippocampus (p<0.05) in the 18mg group, while hippocampal Iba1 staining was increased in the 0mg group.

Conclusions: Third hand exposure to nicotine and nicotine-free e-cigarettes leads to changes in cognitive function and numbers of astrocytes and microglia in the hippocampus.