If you have a 3D printer, you need to make sure it’s in a well-ventilated area–and maybe keep it out of a child’s room–because across the board, 3D printers release tiny, undetectable materials that could be toxic and embed themselves into your body permanently.

This advice comes courtesy of Georgia Tech professor Dr. Rodney Weber, who recently oversaw a landmark study on the emissions of 3D printers that was published in Aerosol Science and Technology. Part of a broader collection of research four years in the making, the study sought to standardize the way we measure the particulates put out by 3D printers so that we might one day certify some 3D printers and their components as healthier than others on the market.

Numerous studies have already confirmed that when 3D printers melt down plastic filaments to shape objects, they release nasty stuff into the air–particles as small as 100 microns (meaning they’re roughly 1/10 the diameter of a single bacterium, or 1/1000th the width of a human hair). But as Weber explains, just how much of this stuff went airborne was hard to measure, because every study was looking at a different combination of machines and filaments, with the emissions being measured in different conditions.

“There was no standard, so you can’t really compare the results,” says Weber. Instead of developing yet another methodology, Weber’s team started with a standard we already developed for laser printers–yes, the 2D printers featured in offices everywhere. It basically involves putting a printer in an airtight chamber, and taking measurements while pumping in more air at a precisely controlled rate.

From the new research, Weber’s team discovered a few things. For one, there is no such thing as a 3D printer that doesn’t emit concerning microparticles into the air. Even industrial models that appear sealed, complete with fans and filters, put out measurable particulates.

“We found that helps a little bit but not a lot,” says Weber. “It’s like people in China wearing face masks for the pollution. It doesn’t do much because the particles are so small they go through the cracks.”

Another discovery was that because filaments are actually mixtures of many chemicals–think of them as plastic cocktails. Designed to satisfy all sorts of material and aesthetic properties, the chemicals they released varied wildly from one brand or model to another. And even if a chemical is only a tiny component of the filament, it can still be released in significant amounts into the air.