0614 GMT February 17, 2020
An investigation by Harvard University found that more than one in four of the increasingly popular products harbored bugs known to cause asthma, inflammation and reduced lung function.
In addition, the study revealed that sweet fruity flavors, which are particularly popular among teens, were most likely to carry the toxins, telegraph.co.uk wrote.
Previous research has shown that chemicals linked to severe respiratory disease are found in common e-cigarette flavors.
However, this is the first time scientists have found potentially harmful biological substances in the devices.
Public Health England (PHE) campaigns strongly for cigarette smokers to switch to e-cigarettes, arguing the products are, at worse, only five percent as harmful as traditional smoking.
This stance is coming under mounting criticism, however, from scientists who say it is too early to know the true dangers of vaping.
The Harvard team examined 75 popular e-cigarette products, namely single-use cartridges and e-liquids for refillable devices.
They found that 27 percent contained traces of endotoxin, a microbial agent in agricultural and industrial settings, and that 81 percent contained traces of glucan, which exist in the cell walls of most fungi.
Professor David Christiani, an environmental genetics expert and the study’s senior author, said: “Airborne Gram-negative bacterial endotoxin and fungal-derived glucans have been shown to cause acute and chronic respiratory effects in occupational and environmental settings.
“Finding these toxins in e-cigarette products adds to the growing concerns about the potential for adverse respiratory effects in users.”
Published in the journal Environmental Health Perspectives, the study found that cartridge samples had 3.2 times higher concentrations of glucan than the e-liquid samples.
Glucan concentrations were also significantly higher in tobacco and menthol-flavored products than in fruit-flavored products.
However, endotoxin concentrations were higher in fruit-flavored products.
The research team said this indicates that raw materials used in the production of flavors may be a source of the microbial contamination.
They said the contamination of the products could have occurred at any point during the production process of either the ingredients or the final e-cigarette product.
But they believe that for e-cigarettes using single-use cartridges, the most likely source could the cotton wicks, as both endotoxin and glucan are known contaminants of cotton fibers.
PHE figures show the number of UK children and teenagers trying vaping has doubled in recent years.
Approximately 16 percent of children aged 11 to 18 reported having tried vaping, according to 2018 data, a rise from 8.1 percent in 2014.
The proportion who said they had never tried e-cigarettes fell from 91.5 percent in 2014 to 83.4 percent in 2018.
Last month a Daily Telegraph investigation revealed that Instagram is promoting vaping products to children as young as 13 using cartoons.
The Royal College of Pediatrics and Child Care Health has called for improved restrictions banning e-cigarette adverts from being targeted at minors.
Since 2016 it has been illegal to sell e-cigarettes to under 18s in the UK.
The Advertising Standards Authority said that vaping adverts must not be ‘directed at’ or ‘likely to appeal’ to people under 18 and should also avoid ‘reflecting or being associated with youth culture’.