Xanthan gum is a thickening and stabilizing agent that's used widely in packaged foods and other goods (such as ice cream, salad dressings, cosmetics and medicines). The substance helps salad dressing pour easily from the bottle, makes ice cream taste creamier and allows liquid cosmetics to stay blended while on the shelf.
Xanthan gum is a naturally occurring substance — sometimes seen as a black goop that forms on rotting vegetables — though it's also produced commercially in factories. To make xanthan gum, the bacterium Xanthomonas campestris is added to a liquid solution containing plant materials such as corn, soy or wheat. Fermentation occurs naturally, and the bacteria create xanthan gum as a byproduct.
Of course, the slime excreted by Xanthomonas campestris looks nothing like the finely ground, powdered version of xanthan gum you'll find in supermarket foods. To create this consumer-friendly product, the substance is first removed from fermenting vats, and then dried and milled.
While the U.S. Food and Drug Administration considers xanthan gum safe, there are certain groups of people that should avoid consuming this additive. In 2011, the FDA determined that premature babies should not consume thickening products containing xanthan gum because they may be linked with a life-threatening condition called necrotizing enterocolitis (NEC), in which part or all of a baby's intestinal tissue is destroyed.
The FDA also requires over-the-counter medications containing the substance to bear choking-hazard labels, as these medicines may cause asphyxiation if not taken with enough water.
People with certain food allergies and sensitivities may also react negatively to xanthan gum, which can cause migraines, skin irritation, flatulence and diarrhea.