Miranda P. Ween, PhD, and Laura E. Crotty Alexander, MD, on the Evolving Landscape of Vaping

Although e-cigarettes were originally marketed as tobacco smoking-cessation devices, the true health effects of e-cigarettes are not clear. And with the emergence of the 2019 vaping epidemic, more evidence was desperately needed.

A research team led by Miranda P. Ween, PhD, and Laura E. Crotty Alexander, MD, performed a systematic review1 of recent evidence to gain more insight on the health effects of e-cigarettes. Pulmonology Consultant reached out to the lead researchers for more information about their review and its findings.

Dr Ween is a senior postdoctoral research fellow the Royal Adelaide Hospital and an affiliate lecturer at the at Adelaide Medical School at the University of Adelaide in Australia, and Dr Crotty Alexander is an associate professor of medicine at the University of California San Diego and a pulmonary critical care specialist and researcher in the VA San Diego Healthcare System in San Diego, California.

PULM CON: Because e-cigarettes are relatively new products in the market, little is known about the long-term health effects of vaping. Therefore, you and your colleagues analyzed current available data on the health effects of e-cigarettes. What harms and/or benefits of vaping did you find for nonsmokers?

Miranda Ween: This is still an area of research in its infancy, but we are seeing more and more studies investigating a wide range of effects. In in-vitro models, we have seen negative implications for infection clearance, altered inflammation response (but the effects on different cells in the lung seemed to vary), and of course varying levels of toxicity. In animal studies, we have seen development of lung cancer and damage to the lungs and other organs from longer-term exposure models. In humans, we see negative implications for cardiovascular health.

Laura Crotty Alexander: Overall the findings published to date suggest that nonsmokers who use e-cigarettes will be at risk for developing both cardiopulmonary and renal disease.

PULM CON: One of the most common arguments used to lobby for less regulations of e-cigarettes is the idea that e-cigarettes are “safer” than smoking tobacco. What did you find regarding the safety of e-cigarettes among smokers?

MW: For smokers, the story is a little murkier due to very few studies having been done, a lack of in-vitro models to represent smokers, and no animal studies yet representing “switchers” and “dual users.” There are a few human studies that suggest cardiovascular health improvements for smokers who switch to e-cigarettes, but unfortunately these studies often did not include smokers who quit using nicotine replacement therapy (NRT) or quit cold turkey, so there is no solid data yet to support the concept that switching to e-cigarettes is as beneficial for your health as quitting smoking. This also means that it is important for patients who have already switched to vaping to be supported in quitting tobacco (e-cigarettes) altogether. 

PULM CON: What are the risks and/or benefits of vaping among patients with respiratory disorders or chronic pulmonary diseases?

MW: This is also an area with very few studies. There are papers that do suggest that patients with asthma who smoke may have improved asthma symptoms if they switch to vaping. However, patients with asthma and chronic obstructive pulmonary disease (COPD) already have an altered lung environment, so it is really important that future studies look at how vaping may affect these groups’ lungs differently than nonsmokers and smokers without existing lung disease. The few studies that have been published show that COPD and asthma cells may experience greater adverse effects from e-cigarettes, thus it is important that patients with these lung diseases who do not currently smoke do not come to perceive e-cigarettes as safe for them to use, and patients who have already switched should be guided to then quit e-cigarettes as well. 

PULM CON: How do different chemical flavorings affect the risk of harm to the lungs? Are some flavorings more dangerous than others?

MW: This is an area of research I, myself, am involved in. The data is becoming increasingly clear that different flavors may not only be more toxic to lung cells (and other cells from outside the lung) but also may affect the function of immune cells. But it is very difficult to compare results from different labs because each banana e-liquid, for example, of the hundreds of banana e-liquids being sold around the globe will have different flavoring chemicals in them (most e-liquids are not just flavored with one flavoring chemical) and the concentration of these chemicals vary massively too. A lot of the research so far has focused on the names of the e-liquids, but we now need to dive deeper into which chemical flavorings can cause what effect, how combinations with other flavoring chemicals could change that, and whether concentration is a factor. A flavoring chemical might be a lot safer if there is a limit to how much can be put into an e-liquid, and if e-liquids are only allowed to contain a single flavoring chemical.

PULM CON: One of the main concerns surrounding the 2019 vaping epidemic was the fact that e-liquids are not regulated—in addition to the fact that youth were buying e-liquids through the internet from unknown sellers. Do you think that regulating e-liquids would reduce the risk of harm?

MW: There is an awful lot of appeal of e-cigarettes for smokers, but the advantage of NRT is the fact that it is regulated by the US Food and Drug Administration, which means quality control and safety testing. Whilst the majority of the e-cigarette or vaping-associated lung injury (EVALI) crisis cases are believed to be linked to counterfeit products, it does raise the point that there are no licensed e-cigarette products and no quality control and safety standards. This puts users at risk because there is no assurance that whatever they inhale into their lungs is safe. E-liquid and vaping device manufacturers are not required to have good manufacturing practice or aseptic technique training. The EVALI epidemic also shows that heating and inhalation of the wrong chemical can results in serious illness and even death. But when it comes to regulation, you have to be careful, particularly with the United States’ proposed flavor ban. Whilst the ban is more about limiting youth uptake by removing the flavors most attractive to them, it can also result in the perception that the permitted flavors to use are safe, and this may not be the case. A more thorough, thoughtful approach may be needed.

LCA: Another consideration is that banning e-cigarettes or flavored e-liquids at this point will likely drive users to buy these from sources outside the country (via online ordering), where there would be even less likelihood of quality control and safety regulations. Instituting a limit as to the nicotine concentration allowed within e-liquids might have a more powerful effect on limiting new users (by decreasing the addiction potential).

PULM CON: What questions are you still looking to answer regarding the effects of vaping among smokers vs nonsmokers?

MW: I think there are a few really big gaps in existing knowledge of e-cigarettes and their health impacts.

  1. How can vaping affect a fetus before and after birth?
  2. Can an already-compromised lung alter how your lungs are affected by e-cigarettes?
  3. Are there any risks/benefits for smokers who switch to e-cigarettes?
  4. Does dual use lead to worse effects than use of either one alone?
  5. How do flavoring chemicals interact with each other, and does this change their safety profile? Is there a concentration factor involved in this?
  6. What effects are there beyond the lungs?



  1. Bozier J, Chivers EK, Chapman DG, Larcombe AN, Bastian N, Masso-Silva JA, Byun MK, McDonald CF, Alexander Crotty LE, Ween MP. The evolving landscape of electronic cigarettes: a systematic review of recent evidence [published online January 29, 2020]. CHEST.