Synthetic cooling ingredients added to e-cigarettes can trigger irregular heartbeats and increase cardiovascular risk, according to a study published today in Circulation: Arrhythmia and Electrophysiology, a peer-reviewed journal of the American Heart Association. The findings, based on experiments in mice and lab-grown human heart cells, suggest that popular coolants like WS-3 and WS-23 may pose a hidden danger to heart health.
Researchers found that when mice inhaled aerosols from e-cigarettes containing nicotine plus synthetic coolants, they experienced more premature heartbeats compared to those exposed to nicotine alone. WS-23 tripled the number of premature beats, while both coolants disrupted heart rate variability—a marker of stress that increases risk for hypertension and arrhythmias. In human heart cells stressed with hormones, coolants slowed the rhythm and altered electrical recharge timing, mimicking conditions that can lead to sudden cardiac arrest.
“Because synthetic coolants create a chilling sensation without flavor, they fall outside of e-cigarette restrictions that focus on ‘characterizing flavors,’” said Alex Carll, Ph.D., M.S.P.H., principal investigator and associate professor at the University of Louisville. “Coolants are added to e-cigarettes at very high levels, often more than nicotine or any other flavoring.” The study is the first to show that these agents may independently harm the heart, separate from nicotine.
The U.S. restricts many flavored e-cigarettes but exempts menthol and cooling agents. Sales of e-cigarettes with synthetic coolants surged 872.1% between 2020 and 2023, according to a 2024 report from the CDC Foundation and Truth Initiative. Meanwhile, menthol-flavored e-cigarette sales rose 175.8% from 2019 to 2023. “This research is timely since menthol and cooling flavors are becoming more popular,” said Jason J. Rose, M.D., M.B.A., of the University of Maryland School of Medicine, who was not involved in the study.
Carll emphasized that policymakers should reconsider regulations: “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.” The study’s limitations include use of male mice only and simplified e-liquids; real-world products often contain additional flavorings. “It’s still unclear how coolants affect people with higher risk for heart conditions, including pregnant women and those with hypertension, heart disease, or diabetes,” Carll noted.
The American Heart Association’s 2023 scientific statement on Cardiopulmonary Impact of Electronic Cigarettes and Vaping Products called for more long-term research. “While the FDA authorizes some flavored e-cigarettes for adults, this does not mean they are safe,” Rose said. “It is important for parents to talk with their children to make sure they understand that no vaping or tobacco product is safe or risk-free.”
E-cigarettes are battery-operated devices that heat a liquid solution into an aerosol inhaled into the lungs. Most contain nicotine, solvents, and often cooling agents and flavors. The study tested e-liquids with 2.5% nicotine benzoate alone or with menthol, WS-3, or WS-23. Mice were exposed while cardiac responses were monitored, and human heart cells were tested with coolants and noradrenaline to mimic nicotine’s stress effects. Coolants did not significantly increase nicotine absorption in mice, but the small blood sample size limits conclusions.
“Together, these findings suggest coolants could cause arrhythmias by making the heart electrically ready too soon or too late for the next beat,” Carll said. “Tobacco-flavored vapes do not disrupt cardiac conduction as much as those with menthol or synthetic coolants. Coolants, especially WS-23, intensified the cardiovascular effects, causing more mistimed heartbeats and greater signs of fight-or-flight stress responses, which increase the risk of dangerous arrhythmias and sudden cardiac arrest.”
