The rapid emergence of nanotechnology suggests that size does, indeed, matter. It turns out that if you break common substances like silver and nickel into really, really tiny particles—measured in nanometers, which are billionths of a meter—they behave in radically different ways. For example, regular silver, the stuff of fancy tableware, doesn't have any obvious place in sock production. But nano-size silver particles apparently do. According to boosters, when embedded in the fabric of socks, microscopic silver particles are "strongly antibacterial to a wide range of pathogens, absorb sweat, and by killing bacteria help eliminate unpleasant foot odor." (By most definitions, a particle qualifies as "nano" when it's 100 nanometers wide or less. By contrast, a human hair clocks in at about 80,000 nanometers in diameter.)

According to the Project on Emerging Nanotechnologies (PEN)—a joint venture of Virginia Tech and the Wilson Center—there are more than 1,600 nanotechnology-based consumer products on the market today. If SmartSilver Anti-Odor Nanotechnology Underwear sounds like a rather intimate application for this novel technology, consider that the PEN database lists 96 food items currently on US grocery shelves that contain unlabeled nano ingredients. Examples include Dannon Greek Plain Yogurt, Silk Original Soy Milk, Rice Dream Rice Drink, Hershey's Bliss Dark Chocolate, and Kraft's iconic American Cheese Singles, all of which now contain nano-size titanium dioxide. As recently as 2008, only eight US food products were known to contain nanoparticles, according to a recent analysis from Friends of the Earth—a more than tenfold increase in just six years.

All of which raises the question of safety. Radically miniaturized particles are attractive to the food and textile industries for their novel properties. Nano-size titanium dioxide, for example, is used as a color enhancer—it makes white foods like yogurt and soy milk whiter, and brightens dark products like chocolate. But what unintended effects might it have?

That's where the nano story gets murky. Remarkably, the US Food and Drug Administration, which oversees the safety of the food supply, both 1) acknowledges that nanoparticles pose risks that are substantially different from those of their regular-sized counterparts, and 2) has done nothing to slow down their rapid move into the food supply.

Back in 2012, the FDA released a draft, pending public comment, of a proposed new framework for bringing nano materials into food. The document reveals plenty of reason for concern. For example: "so-called nano-engineered food substances can have significantly altered bioavailability and may, therefore, raise new safety issues that have not been seen in their traditionally manufactured counterparts." The report went on to note that "particle size, surface area, aggregation/agglomeration, or shape may impact absorption, distribution, metabolism and excretion (ADME) and potentially the safety of the nano-engineered food substance."

What FDA is saying here is obvious: If nanoparticles didn't behave differently, the industry wouldn't be using them in the first place.

So what's the remedy? Rather than require rigorous safety studies before companies can lace food with nanoparticles, the FDA's policy draft proposes "nonbinding recommendations" for such research. Even that rather porous safety net doesn't yet exist—the agency still hasn't implemented the draft proposal it released more than two years ago.

Meanwhile, according to the Friends of the Earth report, nano-laced food products are "entering the market at a rate of three to four per week." And there's real evidence that the small stuff poses significantly higher health risks. For example, in 2011, the National Institute for Occupational Safety and Health (NIOSH) looked at the lung cancer risk faced by workers exposed to air containing various forms of titanium dioxide dust. The agency recommended sharply lower exposure limits for titanium dioxide in its nano form—the stuff they're putting in yogurt and soy milk—reflecting "greater concern for the potential carcinogenicity" of the nano particles, because "as particle size decreases, the surface area increases (for equal mass), and the tumor potency increases per mass unit of dose."

Of course, breathing in nano-size titanium dioxide isn't the same as ingesting it in yogurt. But making stuff really tiny changes the way it behaves in our bodies—and the FDA should respond to its own concerns by making the food industry sweat the safety of the small stuff, before they feed it to us.