You may have heard e-cigarettes are better for you than traditional cigarettes—and to some extent, that’s true: They contain fewer toxic chemicals than regular smokes, according to Hopkins Medicine. But that doesn’t mean e-cigarettes are actually healthy.

And now there’s a new reason to avoid them: The flavoring (called “e-liquid”) may up your risk of heart disease, according to a new study in the Journal of the American College of Cardiology. Researchers at the Stanford University School of Medicine found that e-liquids harm the endothelial cells that line blood vessels and the heart. Along with causing increased DNA damage and cell death, the liquids also appear to interfere with blood vessel growth.

The study tested six popular flavors: tobacco, menthol, fruit, sweet tobacco with caramel and vanilla, sweet butterscotch, and cinnamon. Menthol and cinnamon were found to be the most harmful.

“Until now, we had no data about how these e-liquids affect human endothelial cells,” said senior study author Joseph Wu, M.D., Ph.D., director of the Stanford Cardiovascular Institute and professor of cardiovascular medicine and of radiology. “This study clearly shows that e-cigarettes are not a safe alternative to traditional cigarettes. When we exposed the cells to six different flavors of e-liquid with varying levels of nicotine, we saw significant damage… Continue reading.