Some of the most popular electronic cigarette brands sold in the US are contaminated with bacterial and fungal toxins that can result in health problems, including asthma, reduced lung function, and inflammation, according to a recent study.

One-in-five US teens use e-cigarette products, exceeding the reported use of cigarettes, chewing tobacco, cigars, or hookahs. Though previous research has examined the environmental and physiological impacts of e-cigarette use in teens, researchers say this is the first study examining the potential for microbial contamination.  

Publishing their work in Environmental Health Perspectives, Harvard researchers examined 75 popular e-cigarette products that were either single-use cartridges or refillable e-liquids. Altogether, 37 cartridges and 38 e-liquid products used to refill them were screened for the presence of endotoxin and glucan, including flavors such as tobacco, menthol, fruit, and “others” like java jolt, pina colada, and vivid vanilla.  

They found that more than one-quarter of these products contained traces of endotoxin (or lipopolysaccharide), a toxin found inside bacterial cells that are released when the cell disintegrates. Clinical trials show that when endotoxin is given in small amounts to humans, it triggers a set of responses similar to those seen in true bacterial infections, including respiratory problems. Alarmingly, 81 percent of these products contained glucan – naturally occurring sugars found in the cell walls of most fungi, plants, and certain bacteria and fungi – and has been linked to lung inflammation in smokers.

"Airborne Gram-negative bacterial endotoxin and fungal-derived glucans have been shown to cause acute and chronic respiratory effects in occupational and environmental settings," said David Christiani, senior author of the study, in a statement. "Finding these toxins in e-cigarette products adds to the growing concerns about the potential for adverse respiratory effects in users."

Typically found in agricultural products, endotoxin levels were higher in fruit-flavored products, indicating raw material used in the production of fruity flavors might be a source of contamination. Meanwhile, glucan was more often seen in tobacco and menthol flavors, while cartridge samples were shown to have glucan concentrations that were three times higher than e-liquids. The researchers are quick to note that the contamination of the products could have happened at any point in the production line, or even after the e-cigarette was finished. One hypothesis is that cotton wicks used in cartridges may be a source of contamination as endotoxin and glucan are known contaminants in cotton fibers.

E-cigarette use has skyrocketed in recent years, particularly among high school and middle school students. Estimates suggest that more than 3 million high school students used e-cigarettes last year – a 13-fold increase from 2011.

Limitations of the study include the relatively small sample size. Researchers say that further studies with larger representative product samples are needed to confirm the findings, as well as to identify sources and routes of contamination and to evaluate the health effects associated with contaminated products.