While all e-cigarettes emit harmful chemicals, factors such as the temperature, type and age of the device play a role in emission levels, a new study says.
The study from Lawrence Berkeley National Laboratory (Berkeley Lab) in the US found that e-cigarettes can lead to emissions of toxic chemicals such as acrolein and formaldehyde.
To test effects due to device ageing, researchers used a single device over nine consecutive 50-puff cycles without cleaning.
Emissions of formaldehyde, acetaldehyde, and acrolein - all either carcinogens or respiratory irritants - increased with usage, showed the findings published in the journal Environmental Science & Technology.
"In some cases we saw aldehyde levels increase 60 per cent between cycles one and nine," said co-author and Berkeley Lab researcher Mohamad Sleiman.
The team of researchers simulated vaping using three types of e-liquids in two different vaporisers operated at various battery power settings.
The researchers used gas and liquid chromatography to determine what was in the vapour, looking at the first puffs as well as later puffs after the device heated up and reached a "steady state."
One finding was that the first and last puffs produce widely varying emissions.
Using a custom-built vaping apparatus emulating realistic vaping habits, researchers drew on the e-cigarette by taking puffs lasting five seconds every 30 seconds.
They found that vapour temperature rose quickly in the first five to 10 minutes until reaching a steady state temperature at around the twentieth puff.
Correspondingly, emissions levels between the first few puffs and the steady state increased by a factor of 10 or more in some cases, depending on the device, the battery voltage, and the emitted compound.
For example, for acrolein, a severe eye and respiratory irritant, a single-coil e-cigarette operated at 3.8 volts emitted 0.46 micrograms per puff in the first five puffs, but at the steady state it emitted 8.7 micrograms per puff, the study said.
The results do not mean that e-cigarettes are safe to use at lower temperatures, the researchers said.
"We found there are emissions of toxic chemicals at any temperature at which you use the device," Berkeley Lab researcher and the study's corresponding author Hugo Destaillats said.
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