The Marini study demonstrates that electronic cigarettes do lead to a reduction in exhaled nitric oxide, which suggests that they have a mild respiratory irritant effect and induce some inflammation in the airways. This is a finding which has been reported previously in a number of studies. It is not surprising because propylene glycol is known to be a mild respiratory irritant.

Jacob Sullum provides an of the literature on this topic, pointing out that there is very strong data to demonstrate that the flavors are what attract many smokers to try to quit using electronic cigarettes. You have to read his whole column, but to summarize:

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