July 23, 2015 -- The smallest ingredients found in certain food products are raising concerns among some scientists and food safety advocates.

Known as nanoparticles, these tiny additives -- most often used to make foods more visually appealing -- have an unknown impact on human health. Some studies suggest that eating them may cause inflammation of the digestive tract, damage DNA, and harm cells. These studies have been done in mice or in a lab, though, often using massive amounts of particles that we wouldn’t eat in real life.

Titanium dioxide, the most common nanoparticle in food, helps make candy such as gummy bears opaque, and it enhances colors. Most often, though, it’s used to add a brilliant whitening effect to foods such as powdered doughnuts. It does not add any nutrition.

The FDA has classified titanium dioxide as "GRAS," or generally regarded as safe.

But food manufacturers and suppliers of titanium dioxide are introducing potential risks for no good reason, says Danielle Fugere, president and chief counsel of As You Sow. The advocacy organization promotes environmental and corporate social responsibility, and it pushed Dunkin’ Donuts to phase out the ingredient. The company agreed to do so earlier this year.

“What are the benefits versus the potential downside? The benefits are not particularly compelling,” Fugere says. “We can deal with a slightly less bright doughnut.”

The concern over nanoparticles, as with many other additives, points to a fundamental problem: Critics say ingredients aren’t adequately tested for safety before they're added to processed foods.

In the meantime, we're eating more nanoparticles. One study estimated that between 150 and 600 foods with nanoparticles are on the market, with hundreds, perhaps thousands more, in development.

“We’re quite a long way away” from fully understanding the potential impact, says Andrew Maynard, PhD, professor of environmental sciences and director of the Risk Science Center at the University of Michigan. “It’s been under-investigated.”

Harvard School of Public Health research associate Georgios Pyrgiotakis, PhD, says their microscopic size can drastically change the way the particles move and interact with human cells.