E-cigarette users have been warned of the dangers of not cleaning devices properly over fears harmful bacteria could enter the body from a dirty mouthpiece.
Academic Dr Suzi Gage, who studies recreational drug use, said moisture associated with inhaling vapour may harbour harmful germs.
And if the e-cigarette or vaping device was not cleaned regularly enough it could lead to the user becoming ill, she suggested.
Dr Gage said “surprisingly little” was known about the health risk of nicotine.
She said: “We know what it is about tobacco cigarettes that is so risky to health, it’s the tar, the carbon monoxide, the formaldehyde, the heavy metals and the tens or even hundreds of carcinogens within the tobacco.
“These things either are not present in e-cigarettes, they don’t contain tobacco itself, or they might be present but orders of magnitude lower than in cigarettes.
“Now this doesn’t mean that e-cigarettes are harmless because there might be other aspects of inhaling heated vapour that are risky that we don’t know about yet.
“For example, perhaps the moisture associated with vapour could harbour bacteria, particularly as these devices are re-used rather than single use in the way that cigarettes are.
“If you’re an e-cigarette user, have a little think about how often you clean the mouthpiece that you’re putting in your mouth and inhaling your vapour through.”
Earlier research suggested vaping alters the bacteria in the mouth, making e-cigarette users more prone to inflammation and infection than non-smokers.
It is widely known that traditional tobacco cigarettes increase the risk of gum disease and infection, but there is little knowledge about the impact of e-cigarettes.
It is estimated that 3.6 million people use e-cigarettes in the UK and the Medicines and Healthcare products Regulatory Agency (MHRA) said two people had potentially died from vaping.
In the US, the deaths of 54 people had been linked to the use of vaping illicit liquids containing Vitamin E acetate.
Dr Gage, a psychologist and epidemiologist at the University of Liverpool, said: “This is something that’s known to be toxic or very, very harmful if inhaled.
“Individuals have been using unregulated e-cigarette liquids often containing cannabis or more, usually THC extracted from cannabis, often obtained on the black market and absolutely not a regulated product.
“The outbreak of illnesses and deaths was of course extremely worrying but it led to some countries calling for e-cigarettes to be banned.
“Now, in my opinion, this is akin to someone going blind after drinking bathtub moonshine and suggesting this means we should ban gin and tonics.
“It’s not e-cigarettes themselves that were causing the harm. It was unregulated products being used in any cigarette device.”
Dr Gage, who was speaking at an event at the digital Cheltenham Science Festival, said non-smokers would be “foolish” to start vaping or use an e-cigarette.
“However, for the many thousands or more of individuals who currently smoke and are struggling to stop, e-cigarettes could represent a way to reduce harm,” she said.
