A new study published today in Circulation: Arrhythmia and Electrophysiology, a peer-reviewed journal of the American Heart Association, has found that synthetic cooling agents added to e-cigarettes can cause abnormal heartbeats and increase cardiovascular risk in mice and lab-grown human heart cells. The findings raise concerns that people who use these products may have an increased risk of irregular heart rhythm and possibly sudden cardiac arrest, though these results need to be confirmed by research in people.
The study is the first to show that synthetic cooling agents in e-cigarettes may negatively affect heart health. Synthetic coolants such as WS-3 and WS-23 have become popular in vapes because they reduce harshness and make inhalation feel smoother. Unlike menthol, these coolants create a chilling sensation without flavor, allowing them to fall outside e-cigarette restrictions that focus on characterizing flavors.
According to the study, adding synthetic coolants to e-cigarettes already containing nicotine and solvents increased irregular heartbeats in mice. Specifically, WS-23 tripled the number of premature heartbeats compared to e-cigarettes containing just nicotine and solvents. In human heart cells, the coolants did not change normal resting heart rhythm but, when hormonally stressed, slowed their rhythm and sped up the recharge between heartbeats—effects that could make the heart electrically ready too soon or too late for the next beat, increasing arrhythmia risk.
“Coolants, especially WS-23, intensified the cardiovascular effects of e-cigarette exposures in the mice, causing more mistimed heartbeats and greater signs in heart rhythm of fight-or-flight stress responses, which in turn increase the risk of dangerous mis-timed heartbeats and sudden cardiac arrest,” said Alex Carll, Ph.D., M.S.P.H., principal investigator of the study and an associate professor at the University of Louisville School of Medicine.
Sales of e-cigarettes with synthetic cooling ingredients increased 872.1% between 2020 and 2023 in the U.S., according to a 2024 report from the CDC Foundation and Truth Initiative. The study suggests that coolant levels in vapes should be considered for regulation, especially if further studies confirm that they increase the harmful effects of vaping on the heart. “Because synthetic coolants create a chilling sensation without flavor, they fall outside of e-cigarette restrictions that focus on ‘characterizing flavors,’” Carll noted.
Jason J. Rose, M.D., M.B.A., an associate professor at the University of Maryland School of Medicine who was not involved in the research, commented, “This research is timely since menthol and cooling flavors are becoming more popular. The study results are not surprising because ingredients in e-cigarettes, particularly synthetic flavoring agents, independently carry health risks. We just don’t know the long-term impact of vaping.”
The study leaves several open questions, including how coolants affect people with pre-existing heart conditions, pregnant women, and those with hypertension, heart disease, obesity, or Type 2 diabetes. The authors emphasize that more research is needed, particularly on long-term exposure effects.
The findings underscore the importance of ongoing questions about how flavorings, cooling agents, and product design affect cardiovascular health. As the FDA continues to authorize certain flavored e-cigarettes for adults, this research highlights potential risks that warrant further scrutiny and possibly regulatory action.
