Companies have added thousands of ingredients to foods with little to no government oversight. That’s thanks to a loophole in a decades-old law that allows them to deem an additive to be “generally recognized as safe” — or GRAS — without the U.S. Food and Drug Administration’s blessing, or even its knowledge.
The loophole was originally intended to allow manufacturers of common ingredients like vinegar and table salt — when added to processed foods — to bypass the FDA’s lengthy safety-review process. But over time, companies have found that it’s far more efficient to 
take advantage of the exemption to get their products on shelves quickly. Some of these products contain additives that the FDA has found to pose dangers. And even ingredients the agency has agreed are GRAS are now drawing scrutiny from scientists and consumer groups 
that dispute their safety.
Critics of the system say the biggest concern, however, is that companies regularly introduce new additives without ever informing the FDA. That means people are consuming foods with added flavors, preservatives and other ingredients that are not reviewed at all by regulators for immediate dangers or long-term health effects.
Source: NPR