Vaping or smoking e-cigarettes continues to be popular, especially among young adults. However, new risks keep popping up. The latest comes in a study at the University of California Riverside where researchers found that two toxic chemicals can form when the main ingredient in most e-cigarettes, propylene gycol, is heated. These chemicals, in turn, cause changes in the cells in human lungs. These changes are signs of stress and injury that could contribute to long-term health problems as a result of vaping. Methylglyoxal and acetaldehyde are already recognized as harmful in other settings, their impact during vaping had not been well understood until now. Details are in the journal Frontiers in Toxicology.