Three years ago, researchers at Portland State University in Oregon conducted a study that found previously unknown forms of formaldehyde in the vapor of electronic cigarettes (e-cigarettes).
Following criticism of their work, the researchers revisited their investigation. Their findings are published in the journal Scientific Reports.
This time, they concluded that the risk posed by the formaldehyde content of e-cigarettes is, in fact, greater than they had originally believed.
Formaldehyde is a naturally occurring chemical that is used in the manufacture of building materials and many household products. Industrially, formaldehyde is used as a disinfectant, and as a preservative in medical laboratories and mortuaries.
As well as building materials and cleaning products, formaldehyde can also be found in the smoke from cigarettes, unvented gas stoves, wood-burning stoves, and kerosene heaters.
Since the early 1980s, doctors have suspected that formaldehyde is a carcinogen — a substance capable of causing cancer in living tissue.
And finally, in 2011, after many studies, the Department of Health and Human Services' National Toxicology Program officially confirmed that formaldehyde is a human carcinogen.
What did the original study report?
The original 2015 study that investigated formaldehyde and e-cigarettes was led by David Peyton, Robert Strongin, and James Pankow. It identified new forms of formaldehyde in e-cigarette vapor that were at levels five to 15 times higher than those in normal cigarettes.
The study also found that these new formaldehyde compounds could be drawn much more deeply into the lungs than the "gaseous" formaldehyde in cigarette smoke, because the new compounds bound to particles in the e-cigarette aerosols.
The researchers discovered the formaldehyde compounds when the vaping device in their study was set at a high heat setting. This proved controversial, as some advocates for e-cigarettes argued that most e-cigarette users would not use such a high setting.
This claim was supported by other scientists in 2017 when they attempted to replicate the Portland team's results with the device at a lower heat setting.
What did the new study find?
The Portland team argued that the 2017 reinvestigation of their work was flawed because it ignored the new formaldehyde compounds discovered in the 2015 paper.
Instead, the authors of the replication study simply stated that the more common "gaseous" form of formaldehyde would not affect e-cigarette users at intermediate heats.
In their latest study, Peyton, Strongin, and Pankow used an intermediate power setting that was chosen to represent "normal" vaping conditions. They also claim that they used an improved method to collect samples compared with the original 2015 investigation.
Their new study reports that not only are the new formaldehyde types identified in the 2015 study present when e-cigarettes are used at lower, more "normal" heat settings, but also that gaseous formaldehyde is also present in the vapor at dangerous levels.
As the researchers explain, one limitation of the study is that they did not use human subjects, so we do not know how humans would be affected by the formaldehyde in e-cigarettes.
However, Strongin remains concerned about the public health implications of their findings, saying, "In 2016, more than 9 million Americans were current e-cigarette users, including more than 2 million United States middle and high school students."
"It is thus concerning if even a minority of users cannot properly control e-cigarette-derived intake of formaldehyde and related toxins."