October 9, 2025

expert reaction to study on the health of the offspring of rats exposed to e-cigarette vapour

A study published in the Journal of Physiology looks at the health of the offspring of rats exposed to e-cigarette vapour. 

Prof Michael Ussher, Professor of Behavioural Medicine, University of Stirling, said:

“Like most animal studies, this one found that vaping during pregnancy can be harmful. However, it’s unclear how well these results apply to humans since our bodies, and the way people actually vape, are different from animals. For example, unlike human vapers the animals in this study had no previous experience of nicotine (e.g., most human vapers are likely to be ex-smokers) and they went from no vaping to forced chronic high doses of vaping which is likely to be different than the variable doses and frequencies of vaping which are self-administered in humans.

“The research has the strength that it includes rigorous assessments of the effects on the offspring and includes multiple groups, with and without nicotine.  It has the limitation that it does not include animals that were exposed to smoking, therefore we don’t know the relative effects compared with smoking among this group of animals.

“Most human studies so far suggest that vaping is less risky than smoking during pregnancy. More rigorous studies in humans, especially ones that track children over time, are still needed.”

Prof Caitlin Notley, Professor of Addiction Sciences, Norwich Medical School, University of East Anglia (UEA), said:

“This study exposed laboratory rats to different amounts of e-cigarette vapour during pregnancy to assess health impacts on their offspring. The study randomised rats to the experimental condition and included a control group who were not exposed to any vapour, which is very important to be able to comparatively assess potential health impacts. They also examined high and low wattage exposure and exposure with or without nicotine. The authors conclude that ‘in utero exposure to ecigs from maternal vaping during pregnancy adversely affects the brain development and health of offspring that persist into adult life’. These findings were not related to nicotine, which supports previous research understanding that nicotine is not the most harmful component of either vaping or tobacco smoking.

“This preclinical data is useful in helping us to assess the potential harms of vaping during pregnancy, but is only one piece of the ‘puzzle’. In the real world, pregnant people who are vaping will likely be doing so as a way of quitting smoking, or staying smokefree (relapse prevention). Although there are clearly some potential health risks of vaping to both mothers and babies, the magnitude of those risks is likely to be very much lower than smoking tobacco. It is vital that preclinical (animal) studies are cautiously reported so that pregnant people who smoke are not scared to use reduced harm products, and do not feel stigmatised for doing so, as the alternative of continuing to smoke has very severe health consequences that are much more concerning. Inhalation of burnt tobacco smoke affects oxygen flow through the placenta to the developing baby, directly contributing to low birth weight and other immediate poor birth outcomes.

“The authors say that e-cigarette use has been promoted as ‘safer’ than smoking, but no-one credible has ever claimed they are 100% ‘safe’.  There is likely no ‘safe’ level of exposure to any chemical inhaled into the lung whether you’re pregnant or not, but the important thing is that ecigs are much less harmful in comparison to tobacco, which is why they are supported in England as a harm reduction approach to support people to quit smoking.

“When reviewing the literature on harms of vaping exposure the authors appear to have selected specific studies which support their position.  They do not cite opposing evidence, nor any evidence from more relevant human studies, which would give a much more balanced and objective overview of the current evidence. For example, the authors state that the effect of exposure to e-cigarette vapour ‘are similar to traditional tobacco smoke’. This is simply not the case. We have decades of human studies, including  longitudinal and cohort studies, demonstrating clear causal associations between tobacco smoke and harmful health outcomes such as lung cancer, COPD and cardiovascular disease. We do not have this clear evidence from human clinical studies for e-cigarette vaping, so it is inaccurate and misleading to suggest that tobacco smoking and vaping are almost similar in this way.

“In essence, the findings of this study, if accurately and objectively reported, support the public health approach to vaping in pregnancy adopted in England – that vaping in pregnancy is unlikely to be ‘safe’ or ‘risk-free’, but is likely to be very much less harmful than continuing to smoke tobacco. So, if a pregnant person is struggling to quit smoking, she should be supported to switch to vaping as a reduced harm alternative, if that helps her to quit smoking.”

Dr Jasmine Khouja, Lecturer in Psychology, University of Bath, said:

“Although the study findings hint towards issues that may occur when humans vape in pregnancy, we don’t know that this will happen in humans as we are very different from rats. If we assumed all animal studies translated well to humans, chocolate would be banned because it’s toxic to dogs.

“There are studies in humans that have not shown any indication that vaping in pregnancy is harmful when looking at serious outcomes that can result from smoking in pregnancy, like still births¹. There could be some harm resulting from vaping in pregnancy, but the available evidence suggests that the overall harm would be less than if a person continued to smoke during pregnancy.

“The authors’ claim that nicotine has been blamed for the harmful effects of smoking in pregnancy is true, but actually the evidence to suggest that nicotine is responsible for some of these effects is weak. Nicotine replacement therapies (that contain nicotine) are routinely offered to pregnant people who smoke in the UK. The use of nicotine replacement therapies has been judged to be safe for use in pregnancy, after rigorous studies explored the effects.

“There are some substantial limitations of this study. The rats were exposed to nicotine in a whole-body chamber, which is quite different from how humans vape, so the effects seen may differ to the effects of human use. To avoid harmful emissions, e-cigarette/vape coils should be regularly changed every 1- 2 weeks. If the coils were not changed regularly enough, this could explain why there were poor health outcomes in the vaping groups exposed to nicotine and not exposed to nicotine. I couldn’t see any mention of how regularly these were changed in the study. It’s important to note that there was no group exposed to cigarette smoke to compare to here, so it’s not clear if switching from smoking to vaping may reduce the risk of the harmful effects reported in this study.

“Smoking in pregnancy is known to cause many poor health effects in offspring. Those who are concerned that they may struggle to stop smoking during pregnancy should consult with medical professionals and/or their local stop smoking service to find the right smoking cessation option for them. For those who cannot go cold turkey or use nicotine replacement therapies, vaping may be their best option to have a smoke-free pregnancy.”

¹ https://www.nature.com/articles/s41591-022-01808-0

‘Nicotine influence on cerebrovascular and neurocognitive function with in utero electronic cigarette exposure’ by Amber Mills et al. was published in The Journal of Physiology at 10am UK time Thursday 9 October 2025. 

DOI: https://doi.org/10.1101/2025.02.13.638202

Declared interests

Michael Ussher: “None to declare”

Caitlin Notley: “No conflicts of interest to declare”

Jasmine Khouja: “I have no conflicts of interest to declare.”