Many people assume e-cigarettes are a healthier – or less unhealthy, at least – option than regular cigarettes, resulting in a rapid uptake in recent years. While the long-term effects of e-cigarettes are still unknown, research out of Johns Hopkins University has found that e-cigs may deliver a false sense of security along with their nicotine hit.

The research team from Johns Hopkins Bloomberg School of Public Health found that the vapor from e-cigarettes damages the immune systems of mice and also contains free radical chemicals previously thought to only exist in the smoke from tobacco and air pollutants, albeit at much lower levels – one percent of the 1014 free radicals found per puff in cigarette smoke.

"We were surprised by how high that number was, considering that e-cigarettes do not produce combustion products," says Thomas Sussan, PhD, lead author of the study. "Granted, it’s 100 times lower than cigarette smoke, but it’s still a high number of free radicals that can potentially damage cells."

For the Johns Hopkins study, mice were split into two groups. The first was put into an inhalation chamber and exposed to an amount of the vapor for two weeks that scientists say approximated human inhalation over that time. The other was the control group. After the fortnight, both were divided again into three groups and one from each received, via nasal drops, the bacteria responsible for pneumonia and sinusitis in humans, the second were dosed with Influenza A, while the third received nothing.

They found that the mice exposed to the bacteria or the virus were at a significantly higher risk of exhibiting a compromised immune response if they had been exposed to e-cigarette vapor. In some cases, mice exposed to the vapor and the virus died as a result.

"E-cigarette vapor alone produced mild effects on the lungs, including inflammation and protein damage," says Sussan. "However, when this exposure was followed by a bacterial or viral infection, the harmful effects of e-cigarette exposure became even more pronounced. The e-cigarette exposure inhibited the ability of mice to clear the bacteria from their lungs, and the viral infection led to increased weight loss and death indicative of an impaired immune response."

The study's findings are a concern given that, as the study also points out, although first marketed as a quitting aid (their vapor does contain nicotine even if it does smell like dime-store perfume), e-cigarettes are now gaining popularity with a teen market that has never previously smoked.

The e-cig market in 2013 in the United States was worth US$1.7 billion after they were first legalized in 2007 and is estimated to surpass tobacco in another decade. Many people with chronic obstructive pulmonary disease (COPD) have also made the switch to "vaping" believing it to be a healthier alternative, which may indeed be the case.

But considering the size of the industry and the concern expressed by the Food and Drug Administration (FDA), the World Health Organisation (which made headlines by suggesting the products were not safe) and the European Respiratory Society, it is surprising that no in vivo animal studies have been done before.

The human studies, says the researchers, "are limited to very short-term responses". However, researchers from the University of California, Riverside, published a study in 2010 that came to a similar conclusion: e-cigarettes can cause health problems. If they cause the same number of health problems as regular cigarettes does seem unlikely given the toxic cocktail found in cigarette smoke, but more research obviously needs to be done in this area. Of course, the safest course of action would be to abstain from both regular and e-cigarettes.

The Johns Hopkins research was published in the journal PLOS ONE on February 4