Vaping aerosols contain thousands of unknown chemicals and substances not disclosed by manufacturers, including industrial chemicals and caffeine, Johns Hopkins University researchers found.

According to a report published on Johns Hopkins University’s website, the study is the first to apply to vaping liquids and aerosols an advanced fingerprinting technique used to identify chemicals in food and wastewater. Carsten Prasse, an assistant professor of environmental health and engineering, and his team were the first researchers to test vape samples with chromatography/high-resolution mass spectrometry, a chemical fingerprinting technique more commonly used to identify organic compounds in wastewater, food, and blood. Although it's possible to buy vaping products in hundreds of flavours, for consistency they tested only tobacco-flavored liquids sold by four popular brands – Mi-Salt, Vuse, Juul, and Blu. They found nearly 2,000 of unknown chemicals in the liquid, and the number of compounds increased significantly in the aerosol.
Of those the team could identify, six substances were potentially harmful, including three chemicals never previously found in e-cigarettes. Besides caffeine, the team found three industrial chemicals, a pesticide, and two flavourings linked with possible toxic effects and respiratory irritation.
The results are published in Chemical Research in Toxicology.