While Juul may not be connected to the acute lung injuries that have sent more than 2,500 to the hospital since August, a new study from Harvard T.H. Chan School of Public Health suggests that the e-cigarette product may not be the harmless smoking cessation device that Americans were promised.

Published in the American Journal of Respiratory and Critical Care Medicine last week, the study analyzed the contents of 54 Juul pods of varying flavors and found that 46 percent tested positive for a microbial toxin called glucan, a soluble fiber found in fungal cell walls. (The researchers also tested the pods for another substance called endotoxin, which was not detected).

Although benign when eaten, long-term studies have shown that exposure to high levels of airborne glucan can cause severe inflammation in the airwaves. Based on research from the University of Southern California, lung inflammation can fuel a host of harmful conditions in otherwise healthy people, including asthma, emphysema, chronic bronchitis and Chronic Obstructive Pulmonary Disease (COPD).

Out of all the Juul pods tested, tobacco and menthol were found to contain the highest levels of glucan.

The news comes just days after the Food and Drug Administration announced a ban on single-use, flavored e-cigarette cartridges, excluding — interestingly — tobacco and menthol. While the FDA’s decision was aimed at discouraging more teens to take up vaping, the new Harvard study is aimed at investigating the potential longterm damage that 5.3 million teens who already vape may face.

David C. Christiani, MD, a professor of environmental genetics at Harvard Medical School as well as the study’s author, says that the danger that glucan poses to the lungs is well-documented. “We see in certain occupational environments such as textiles, soil, and plywood ... [it] causes inflammation in the lungs,” he says. “That's why we looked at it because these occupational papers have been out for over 20 years.”

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A new study from researchers at Harvard has identified two toxins in Juul pod that have the potential to cause longterm lung damage. (Photo: Justin Sullivan/Getty Images)

The analysis, which will be released in print in the coming months, is a follow-up on a similar April study in which the researchers studied 75 different types of e-cigarettes and found traces of glucan in over 80 percent of products. After the report was released, the pro-vaping advocacy group American Vaping Association (AVA) released a scathing statement calling it “disgraceful” to release the study and attacking Harvard for not including Juul. “This data is based on ancient products that were in use six years ago, meaning that modern devices like JUUL were not studied,” the AVA said, according to the Boston Globe.

Christiani says it was this statement that motivated the researchers to do another analysis, specifically on Juul. “We didn’t use Juul the first time so when they made that comment, we went out and bought a whole bunch of Juul pods right away,” says Christiani. “And the majority of products had glucan.”

While most of the research thus far on the health effects comes from working environments with glucan, those aren’t the only place it poses a risk to humans. Cigarettes have been shown to contain glucan as well — likely at far higher levels than e-cigarettes. It’s for this reason that Greg Conley, president of the AVA, takes further issue with Harvard’s new research.

"Microbial contamination is a reality with everything in life, including e-liquids and traditional tobacco products ... “ Conley tells Yahoo Lifestyle. “These authors have identified no actual risk, just that some microorganisms were detected, and they are promoting their findings knowing that many will falsely interpret the paper to mean that vaping could be equally or more hazardous than smoking cigarettes.”

Conley further attacks the authors’ mention of the EVALI cases — the e-cigarette and vaping product-use associated lung injury — and expresses concern that users will blame Juul for these acute lung injuries. But Christiani is clear that the study is drawing no connection between the toxins found in Juul and the hospitalizations that are occurring nationwide for mostly black-market vaping products.

“We don’t think glucan is explaining this acute lung injury epidemic, where a lot of focus is now appropriately on oils like vitamin E acetate,” Christiani says. “We were looking at the bigger picture and the more chronic conditions and we're doing these things several years now before the acute epidemic.” Overall, he stresses that vaping products are not a good idea. “These are not healthy things to be inhaled.”

Juul did not reply to Yahoo Lifestyle’s request for comment.

And while Juul may not be responsible for the short-term lung injuries that have killed more than 50 Americans, the company has been implicated in the spike in vaping use among teens. According to the New England Journal of Medicine, vaping use doubled among 8th to 10th graders from 2017 and 2019, a statistic that the CDC has traced to marketing from companies like Juul.

Juul has taken a major hit as a result, going from a perceived market value of $38 billion in under $20 billion. But the company has repeatedly defended its product, presenting a clinical trial in February which claimed that switching to Juul was as beneficial as quitting smoking entirely. Since then, the Food and Drug Administration has announced that Juul and other e-cigarette companies have until May this year to submit evidence that backs up their health claims — or else risk being removed from the market.

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