Vaping is a fairly new phenomenon. Electronic cigarettes have only been available in the U.S. and Europe for about a decade, and that means we don’t fully understand the long-term effects of vaping on users. However, we do know enough about the likely health risks of vaping — based on the safety profiles of the chemicals involved — to understand that vaping is highly unlikely to pose risks to users as great as those of combustible cigarettes. And we actually know more about the risks of vaping to bystanders. That’s because there are standards for measuring “environmental exposure” (the risk of breathing chemicals in the air) that can be applied to e-cig vapor. Based on government standards for workplace exposure to inhaled chemicals and metals, scientists can estimate whether the toxic constituents present in “second hand vapor” might make vaping harmful to others. And so far, there’s no evidence that second hand vaping is a serious threat to the health of non-vaping bystanders.

What is second hand vapor?

Second hand vapor is the vapor (which is technically aerosol) exhaled into the atmosphere by a vaper. Like second hand smoke, it lingers in the air long enough that anyone in the same room, assuming it’s small enough, is likely to inhale some of the exhaled aerosol. As the name indicates, the bystanders are not inhaling second hand smoke — because second hand e-cigarette vapor simply isn’t smoke. Smoke is a product of combustion. Burning any substance with fire — including wood, leaves, a building, or tobacco — produces volatile gasses, carcinogenic particles, carbon monoxide, and a mixture of dangerous byproducts that in cigarette smoke are called tar. Second hand smoke isn’t as dangerous as inhaling directly from a cigarette, but prolonged exposure to it is considered a serious hazard. Vapers produce clouds of vapor by heating e-liquid with an atomizer that houses a small metal coil, which turns it into the vapor you see. The vapor from e-cigs doesn’t have any carbon monoxide or tar. Dangerous chemicals and metals are found in vapor, but in very small amounts. The levels of toxicants are tiny compared to those in smoke, which means the dangers of second hand vaping are even less significant.

What’s in second hand vapor?

If you encounter people vaping inside a house, all of the second hand vapor you see comes out of the lungs and mouths of the vapers in the room. There is no side stream “vape smoke,” like there is with cigarettes — no constant emission of vapor pouring from the device. The vaper has to inhale to produce vapor. And by the time they exhale, there’s a lot less of all the substances found in the vapor, because the users absorb most of it in their lungs, throats, and mouths. Vaping second hand isn’t really a thing, because the bystanders are getting so little of the contents of the vape. Aside from propylene glycol and glycerin — the two glycols that together make the base of all e-liquids — what vapers exhale into the air doesn’t contain high levels of anything. According to Drexel University toxicology expert Igor Burstyn, while the contents of e-cig vapor inhaled by users “justifies surveillance,” there is so little contamination in exhaled vapor that there is unlikely to be any risk. What isn’t inhaled falls to the ground. Those concerned with “third-hand nicotine” — the unabsorbed nicotine that lands on floors and furniture — might make a case for not vaping around kids or pets who might lick the surfaces. But there’s not much nicotine left in the settled residue. According to a 2016 University of California-San Francisco study, 93.8 percent of the inhaled nicotine is retained by the user, and is not part of the exhaled vapor. “Nicotine from exhaled vapour can be deposited on surfaces, but at such low levels that there is no plausible mechanism by which such deposits could enter the body at doses that would cause physical harm,” said the Royal College of Physicians in its 2016 review of e-cigarette science. Particles from vaping, which are liquid rather than solid like smoke particles, don’t seem to affect air quality at all. In a 2017 University of California-San Diego study that studied the air in 193 low-income family homes, the researchers found that smoking tobacco or marijuana, cooking, and burning candles all affected particle counts in the homes. But vaping (which happened in 43 of the homes) had no measurable effect on the indoor air quality. Even second hand vape studies of the air in vape shops have shown that levels of toxicants are below occupational exposure limits. In fact, the National Institute for Occupational Safety and Health (NIOSH — a CDC agency) found that even in a shop where 13 customers vaped during the day, the flavoring chemicals and formaldehyde were all below the limits allowed. And nicotine was practically absent from NIOSH’s samples.

Is second hand vapor dangerous?

Looking at the vaping studies mentioned above and others, Public Health England’s 264-page review of available evidence of vaping risks concluded that “to date there have been no identified health risks of passive vaping to bystanders.” Igor Burstyn’s study of the dangers of second hand vaping attempted to “estimate potential exposures from aerosols produced by electronic cigarettes and compare those potential exposures to occupational exposure standards.” He concluded that “Exposures of bystanders are likely to be orders of magnitude less, and thus pose no apparent concern.” Orders of magnitude are multiples of 10 — so, 10-100-1,000-10,000 and so on. What Burstyn means is that the exposure to toxic chemicals in second hand vapor is so slight as to pose no real threat. Whatever the risk to the vaper, it is 10 times, or 100 times, or even 1,000 or 10,000 times lower for the bystander. Does that necessarily mean that vapers should feel free to vape everywhere without regard to the wishes of others? No! Even if second hand vaping can’t be proven harmful to others, the concerns of family and friends need to be respected. Obviously, if a spouse or visitor objects, vapers should be courteous and thoughtful, and take the vape outside. Clearly, if a resident of the home has asthma, second hand vape is best avoided, since we know PG and some flavorings can irritate the airways. And, of course, children don’t get to make an informed choice about what they breathe, so vapers should use their best judgement and probably be more cautious than they would around adults. There are no second hand vapor studies that specifically measure the lung functions of babies or young children after heavy daily vape inhalation. Vapers shouldn’t experiment on their kids.