Those plastics tends to emit styrene, a possible carcinogen, at levels much higher than recommended by California's Office of Environmental Health Hazard Assessment (OEHHA). As a result, the team advised that "caution should be used when operating many printer and filament combinations in enclosed or poorly ventilated spaces or without the aid of gas and particle filtration systems."

PLA users don't have much to worry about, however. Printing with that plastic tends to produce a substance called lactide, which is considered to be non-toxic. The printer itself doesn't matter much, as the researchers saw little difference in fume levels from model to model. Given that, they recommended that manufacturers focus on designing new types of low-emission, PLA-like filament materials, or design printers with built-in gas and particle filtration. They plan to carry out more detailed, real-world studies in the future.