Which is more harmful: secondhand vapor from an electronic cigarette, or the smoke from a stick of incense?

The vapour from an e-cig or personal vapouriser (PV) is mostly water (steam/mist/fog) that has been turned into a mist to inhale and exhale.   It contains much less than any countries minimum allowed levels of all contaminants, plus a tiny amount of the optional nicotine and flavourings.  It does not contain any of the known dangerous products of combustion including tar. An incense stick burns, produces many products of this combustion, maybe some carcinogens (to date I have not found an analysis of this smoke - still looking, and will add edit at bottom if found).        ** See above - awaiting responses, will add at end in edit later. TL:DR The Incense Stick is probably much more dangerous to your health than an e-cig, although less than smoking a cigarette yourself. Edit:- http://www.clinicalmolecularallergy.com/content/6/1/3 Nasty stuff actually... https://e-cigs-board.quora.com/Peering-through-the-mist-What-does-the-chemistry-of-contaminants-in-electronic-cigarettes-tell-us-about-health-risks

Excellent answer by Miles, and I would add this: Temples in which incense is burned can have close to fifty times the concentrations of polycyclic aromatic hydrocarbon (PAH) carcinogens such as benzopyrene as homes where people regularly smoke.  See : http://drbenkim.com/burning-incense-cancer.html for more information. Since electronic cigarette vapor is generally thought to be far less of a threat than tobacco smoke, the comparison with incense would be even more intense. - MJM

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