Researchers from Roswell Park Cancer Institute in the US also confirmed an earlier finding that increasing the battery output voltage of these devices significantly increases toxicity.
"Although many of the flavourings used in e-cigarette liquids have been certified as safe for eating, little is known about their effects when heated and inhaled in e-cigarettes," said Maciej Goniewicz, Assistant Professor at Roswell Park.
"This study suggests that various characteristics of e-cigarettes, including any flavourings, may induce inhalation toxicity and therefore, caution should be used with these products until more comprehensive studies are performed," said Goniewicz.
They evaluated six types of e-cigarette devices filled with liquids of different flavors - tobacco, pina colada, menthol, coffee and strawberry - at several battery output voltages.
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Their findings suggest that the power of the e-cigarette device, as well as the addition of any flavourings, significantly affect the toxicity of e-cigarette aerosol, with strawberry flavourings being the most toxic to users.
"Our study demonstrates that e-cigarette products differ significantly in the degree of their cellular toxicity to bronchial epithelial cells," said Goniewicz.
"Additionally, users may want to reduce their potential harm by choosing products with lower toxicity profile and operating their devices at lower power settings," Goniewicz added.
The study appears in the journal Tobacco Control.