Prenatal Exposure to Vaping Ingredients Alters Skull Development in Mice

A new study conducted on mice has revealed that in utero exposure to two common ingredients found in e-cigarette liquids, excluding nicotine, can influence the shape of a fetus's skull during development.

In experiments involving pregnant mice exposed to combinations of liquids used for vaping effects, researchers found that offspring exhibited narrower facial features and shortened skulls compared to control groups. These changes occurred even though no nicotine was present in the mixtures tested.

The findings were unexpected because the specific chemical ratio known to produce these defects was marketed by the e-cigarette industry as a "safer" alternative to earlier product formulations, according to lead author James Cray, professor of anatomy at The Ohio State University College of Medicine.

"We did not expect to see any developmental changes since there was no nicotine involved," said Cray. The study has been recently published in PLOS One journal.

The developmental biology team at Ohio State has long investigated the impacts of nicotine on head and facial development, previously finding that exposure to nicotine through breastmilk led to skull defects in mice. About 3% of infants worldwide are born with birth defects annually, including issues like cleft lip or palate.

In this study aimed at serving as a control model, pregnant mice were exposed to either clean air or two types of humectants—propylene glycol and glycerol—used as carriers in e-cigarettes. These substances were tested at varying concentrations: 50% each of propylene glycol and glycerol (50/50 mix) and another group with a 30/70 ratio.

While many companies are shifting towards higher glycerol contents to market them as safer, Cray's team observed that mice exposed to the presumed safer 30/70 PG/VG mixture actually displayed more significant alterations. "What we see is a consistent narrowing of all of the facial features and a shorter head shape," said Cray. "These animals weighed less but remained within normal growth parameters."

These outcomes were consistent across multiple litters and both sexes.

The Food and Drug Administration started regulating e-cigarettes in 2016, facing various legal challenges from e-cigarette companies. Researchers continue to study the health impacts of these products as their use grows, especially among young adults and teenagers—many of whom may not realize they are pregnant during critical development stages.

"This small study suggests that nicotine-free vaping might not be safe, signaling we need further research into non-nicotine components," Cray concluded. This collaborative work included researchers from Ohio State University, Nationwide Children's Hospital, the University of Pittsburgh, and UT Health San Antonio.