Objectives: Electronic cigarettes (ECs) have recently become popular around the world, and their safety is being widely discussed in the scientific literature. Previous studies have examined the chemicals in e-liquids and vapour, and demonstrated that the aerosol from ECs can contain toxic chemicals that are harmful to health. However, little is known about the potential adverse health effects of passive exposure to EC vapour. The aim of this paper is to summarise and review all studies that have examined potential adverse health effects of passive exposure from inhaling EC vapour. Specifically, our research objectives were to describe 1) the absolute impact of passive exposure from inhaling vapour when compared with background, and 2) the relative impact of passive exposure from inhaling vapour when compared with passive exposure from inhaling conventional cigarette smoke.

Methods: A systematic review was conducted to identify articles published from 1996 to 10 September 2015 from Embase, Ovid MEDLINE and PreMEDLINE. Papers eligible for inclusion had to be written in English, study health effects from passive exposure to EC vapour in animals or humans, test or analyse the EC vapour directly or in the ambient air (with an inference made about passive or second-hand vapour exposure). The review was conducted using the PRISMA guidelines for reporting on systematic reviews. We identified 312 studies, and 16 were relevant for inclusion in our review.

Results: A variety of study designs were used to investigate potential health risks from passive exposure to EC vapour. These included direct exposure studies involving humans and animals, and indirect exposure studies using volunteer EC users or smoking machines. The majority of studies determined that passive exposure to EC vapour may pose a health risk to bystanders. All papers encountered a number of limitations.

Conclusion: Our review found that the absolute impact from passive exposure to EC vapour has the potential to lead to adverse health effects. The risk from being passively exposed to EC vapour is likely to be less than the risk from passive exposure to conventional cigarette smoke.