The study shows that e-cigarette vapor can do harm although it is not certain it will do harm.
E-cigarettes don't proceed tar or carbon monoxide; two of the main toxins in cigarette smoke, said the NHS.
They extracted immune cells from lung tissue samples provided by eight non-smokers who had never suffered from asthma or COPD and exposed them to varying levels of e-cigarette fluid and condensed vapour.
Some of the effects appear to be similar to effects seen in people with chronic obstructive pulmonary disease (COPD).
He also advised that further research is required to fully understand the long-term health impact of vaping.
Earlier this year, an independent review concluded that e-cigarettes should be available on prescription due to the fact that there is "overwhelming evidence" that they are better for you than smoking.
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While e-cigarettes are safer than traditional cigarettes, they may still be harmful in the long term, Thickett explained as the current body of research is in its infancy and not able to answer that question yet. "And there are some early studies that suggest that people using e-cigarettes have more respiratory symptoms, such as coughing and wheezing, than those using nothing at all".
Previous studies have focused on the chemical make-up of e-cigarette liquid before it is vaped, the researchers said.
In an accompanying podcast, Professor Thickett said the tobacco giants, who have bought up numerous e-cigarette companies, have an agenda to portray e-cigarettes as safe.
After 24 hours of exposure the total number of viable cells exposed to the vaped condensate was significantly reduced compared to the untreated cells, and condensate containing nicotine exaggerated this effect.
Professor John Britton, director of the UK Centre for Tobacco and Alcohol Studies at the University of Nottingham, said: "This [study] indicates that long-term use of electronic cigarettes is likely to have adverse effects, as is widely recognised by leading health authorities in the UK, including the Royal College of Physicians and Public Health England".
Alarmingly, the condensate was found to be more harmful than standard e-cigarette fluid, with the effects worsening as the dose increased. Treatment with an antioxidant, however, restored that ability and helped reduce other damage caused by e-cigarette fluid, Thickett's team found.