Fukuoka, Japan—Electronic cigarettes (e-cigarettes), widely marketed as a safer alternative to traditional cigarettes, are now hooking younger generations. World Health Organization data from 2025 show that at least 15 million adolescents aged 13–15 now vape. As colorful, fruit-flavored devices become a new social norm on playgrounds and campuses, we must rethink whether they are truly harmless as advertised.
A recent study from Kyushu University, with collaborators from Hong Kong and Taiwan, published in Science of The Total Environment , offers biological insights into the potential health risks of vaping. Using a zebrafish model, the researchers show that exposure to e-cigarettes alters gut microbiota composition and affects neurobehavior.
"The gut microbiome is sensitive to environmental exposure, and its balance and stability are closely linked to overall health," notes Tse Ka Fai William , Associate Professor at Kyushu University's Faculty of Agriculture . "We therefore investigated how e-cigarette vapor changes bacterial communities and what that might mean for the organism."
The researchers turned to zebrafish, a commonly used model in toxicology and biomedical research that shares approximately 80% of human disease-causing genes. They designed a water-based exposure system, bubbling e-cigarette liquid—with and without nicotine—into fish tanks over seven days. Doses and device settings mimicked typical vaping conditions, with unexposed tanks used as controls.
Chemical analysis revealed that heating e-cigarette liquids produced harmful byproducts, including formaldehyde and acetaldehyde, which are classified as carcinogens and can cause respiratory and skin irritation.
Following exposure, the researchers found disruptions in the zebrafish gut microbiome, with reduced microbial network stability and altered community composition.
"Some bacteria become dominant and replace others, forming a new microbial community," explains the paper's first author Thi Ngoc Mai Dong, a master's student at Kyushu University's Graduate School of Bioresource and Bioenvironmental Sciences . "The changes suggest that the fish, or rather the bacteria, can 'feel' the toxic substances in the water and want to adapt to the new environment."
For instance, in nicotine-exposed fish, Fusobacteriaceae, key contributors to gut health and mucosal integrity declined significantly, while Sphingomonadaceae, bacteria that known for their ability to degrade xenobiotic compounds, became dominant. In nicotine-free vapor exposures, Shewanellaceae and Barnesiellaceae were enriched, potentially reflecting responses to environmental stresses and altered immune regulation. Bioinformatics analysis further showed enrichment of microbial pathways involved in xenobiotic degradation and oxidative stress responses, suggesting both direct chemical metabolism and secondary stress adaptation.
"We also see that the microbiome is actively breaking down flavoring chemicals in vaping liquids," adds Carl Andersen Macaraeg Tan, an undergraduate student who joined the dual-degree program at Kyushu University's School of Agriculture and the second author. The researchers expressed concern that the chemical compositions of many e-cigarette flavors are not fully disclosed, limiting evidence-based risk assessment.
Given that gut microbial metabolites may influence neurological function, the team further studied zebrafish behavior. They found that regardless of nicotine content, e-cigarette exposure caused behavioral changes and impaired escape responses. The team is now exploring the underlying biological mechanisms and, drawing on its expertise in developmental biology, plans to examine whether vaping exposure of adult fish may affect the health of their offspring.
While based on an animal model and cannot be directly extrapolated to humans, the study aims to raise awareness among the public, educators, and policymakers of the need for further investigation of the potential risks posed by vaping.
"This research was partly motivated by our international students, who noticed e-cigarette use becoming more common among their peers, not only in Japan but worldwide," says Tse. Through the English-taught International Undergraduate Program at the Faculty of Agriculture, Kyushu University provides young students with early research opportunities, and students from diverse cultural backgrounds bring fresh perspectives to global health concerns.
"We hope these findings can make consumers aware that e-cigarettes produce harmful substances, and support more transparent risk communication and regulation," Tse concludes.
