Menthol in e-cigarettes may be harmful to respiratory health, according to a new study by a team of experts at the University of Hawaii at Manoa. The findings come amid rising e-cigarette use among Hawaiian youth.

Izoe, UH Mānoa Professor of Mechanical Engineering and Adjunct Professor of Pediatrics, has invented a groundbreaking method to study the health effects of e-cigarette aerosols. The breakthrough study, published in June 2022 in the American Journal of Physiology—Pulmonary Cell and Molecular Physiology, found that menthol in e-cigarettes caused biophysical inhibition of lung surfactant.

Zuo's research found that the flavorings used in e-cigarettes, especially menthol, damage the lipoprotein membranes on the air-water surface of the lungs. This film is called a pulmonary surfactant. It plays a central role in maintaining the normal respiratory mechanics of the lungs. Therefore, zuo's research suggests that menthol in e-cigarette aerosols may have adverse effects on the respiratory health of users.

"E-cigarettes were first promoted in the mid-2000s as a healthier and safer alternative to traditional smoking," Zuo said. "However, a growing body of research evidence, especially long-term (over 10 years) toxicology data that has only emerged in recent years, suggests that e-cigarettes are not as safe as originally promised."

 E-cigarette use is on the rise among Hawaiian youth, according to a youth behavioral risk survey by the UH Mānoa Institute of Education. From 2015 to 2019, survey respondents who used e-cigarettes or vaping products at least one day in the 30 days preceding the survey increased from 25.1% to 30.6%. In the 30 days before being surveyed, that percentage increased from 3.6 percent in 2015 to 10.4 percent in 2019.

Flavor is the main attraction for e-cigarette users, especially young people. As of 2018, there are over 15,000 different e-cigarette flavor blends on the market to choose from. Although most flavoring agents used in e-cigarettes are food-grade additives and flavors, their safety and health effects on the respiratory system (at the levels inhaled by e-cigarette users) have so far been largely unknown .

Menthol is a substance found in peppermint, spearmint, and other peppermint plants. It gives a cooling and soothing feeling and is used to relieve minor pain and irritation. Menthol is added as a flavoring agent to products including cough drops, beverages, chewing gum and candy.

However, none of these products can be smoked or inhaled while in use. By contrast, e-cigarette companies add menthol to their products to make them more appealing to use and appear less harmful.

Zuo hopes the research findings will contribute to a better understanding of the health effects of e-cigarettes, especially on teens, and better regulation of vaping products.

The research was carried out by Zuo's lab in collaboration with Professors Ellinor Haglund and Rui Sun in the UH Mānoa Department of Chemistry. This research was supported by a National Science Foundation Award and the Hawaii Community Foundation's George F. Straub Trust and Robert C. Perry Fund.