If you’ve ever trailed someone vaping on a crowded street, you can probably relate just a little to Christine in the boat scene of “The Phantom of the Opera.” Following a mysterious stranger, you suddenly become engulfed in a dense, smelly fog with no escape in sight.

Turns out, your experience isn’t so far from the Broadway spectacle as you might think.

Fog machines and vape fluids contain the same ingredients: glycerin and water. Both sometimes use propylene glycol as well (though exceptions exist), and both heat these ingredients to a boiling point to produce vapor.

The only differentiating ingredient between the two vapors is the addition of nicotine or cannabis in vapes.

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But while vape pens are often marketed as a “discreet” and “safe” method of consuming cannabis or nicotine, theatres with fog machines usually advise those with lung conditions to sit far away from the stage. Some also warn of worrisome effects the vapor can have on those without respiratory issues, such as headaches and dizziness, which can arise even from short term exposure.

In sum: even though the ingredients are virtually the same, indirect inhalation of fog machine vapor can mess you up, but secondhand vape exposure is harmless, according to manufacturers. Sound fishy?

Dr. Panagis Galiatsatos, Assistant Professor of Pulmonary and Critical Care Medicine at Johns Hopkins University, thought so. That’s why, when a patient of his was struggling to find relief from hypersensitivity pneumonitis (an immune system disorder in which the lungs become inflamed as a reaction to environmental elements), he and his colleagues tried asking the patient’s husband to stop vaping. Almost immediately after he stopped, the patient began recovering.

“The husband’s vaping was the only thing we removed from the patient’s environment,” Galiatsatos said. “So we knew for certain that the secondhand vape exposure was the cause.”

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The case, published last year, became the first to prove a person’s health can be affected by secondhand vape exposure. Galiatsatos said that many doctors had suspected it in the past, but none had been able to prove it.

“Consuming secondhand vapor from vape pens is consuming toxins – there’s no other way to spin it,” Galiatsatos said. “They can house tons of bacteria in them and are triggering for people with asthma – just the same as fog machines, which we know are irritant to the airways. I believe we will see more long-term health consequences resulting from this (secondhand exposure to vaping) in the future.”

Galiatsatos said his findings led him to believe vaping legislation should parallel that of alcohol in the U.S., with well-known regulations and restrictions for the youth. His alarm, he said, primarily results from the implications of secondhand vape exposure for children, the elderly, and those with underlying respiratory issues.

“Everyone should be avoiding this – everyone, and especially kids,” Galiatsatos said. “Children’s lungs continue forming until ages eight to 12, so vaping around them could rob them of their potential lung capacity. We know smoking tobacco around them does, so we assume vaping is the same.”

Those ages 65 and older are at particular risk when exposed to cannabis vapes. A growing amount of research is showing many cardiac issues senior citizens experience can be directly associated with cannabis exposure.

Even so, vapes don’t seem to be in any rush to leave. The industry, though mostly illicit, is booming around the country, even in states where marijuana is completely illegal, and teens are its most avid consumers.

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We asked Heather Despres, Director of Patient Focused Certification at Americans for Safe Access, a cannabis advocacy organization, what the future of vape regulation might look like in light of the danger of secondhand exposure. Her answer was that states should be testing vapes to ensure these tiny fog machines are, at least, not harboring pesticides and heavy metals that could cause fatal illnesses.

“There are states, particularly Colorado, that are going to begin requiring testing on vape pen vapors, looking specifically at heavy metals content,” Despres said. “California also requires vape pen testing for Vitamin E acetate. My hope is that we will see a lot more testing and regulation of these products in the future.”

If you’re worried about vaping, or your partner’s vaping, edibles are one of the safer ways to consume your cannabis.

Elissa Esher is Assistant Editor at GreenState. Her work has also appeared in The Boston Guardian, Brooklyn Paper, Religion Unplugged, and Iridescent Women. Send inquiries and tips to elli.esher@hearst.com.