Researchers from the University of Rochester suggest the harm begins when the e-cigarette's heating element is activated.
The heating element is designed to turn a liquid solution (known as an e-liquid or "juice") into an aerosol that mimics cigarette smoke.
The inhaled vapours contain heavy metals and other possible carcinogens in the form of nanoparticles - tiny particulate matter that can reach farther into lung tissue, cell systems, and blood stream.
Irfan Rahman, professor of Environmental Medicine at the UR School of Medicine and Dentistry, led the research which also found that some flavoured e-juices (particularly cinnamon) create more stress and toxicity on lung tissue.
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Mice exposed to e-cigarettes with classic tobacco flavouring also demonstrated signs of pulmonary inflammation.
"Several leading medical groups, organisations, and scientists are concerned about the lack of restrictions and regulations for e-cigarettes," Rahman said.
"Our research affirms that e-cigarettes may pose significant health risks and should be investigated further. It seems that every day a new e-cigarette product is launched without knowing the harmful health effects of these products," he said.
The study is published in the journal PLOS ONE.