Xanthan gum was discovered in the 1960's by researchers in the US Department of Agriculture. It is a microbial polysaccharide that results from using the bacterium Xanthomonax campestris in the natural fermentation of glucose or sucrose (typically sugar from corn or cabbage).
Due to its ability to greatly increase the viscosity of foods, xanthan gum plays an invaluable role in gluten-free baking. Just a very small amount provides a ‘stickiness' and structure to the dough, which, without gluten, could end up a flat crumbly mess.
Other products that commonly use xanthan gum are salad dressings, ice creams, sauces, toothpaste, cosmetics and Fake Blood!
Since the glucose used in the fermentation is often corn derived, some people severely allergic to corn may also react to it; however, the protein is not in the glucose, so usually xanthan gum will not provoke a reaction in somebody with a corn intolerance.