In addition to the soy lecithin problem, and aspartame, (which many of us react to), most gum contains one or more of the sugar alcohols, xylitol, manitol, maltitol, or sorbitol. Many of us, (including me), react to the sugar alcohols, and soy lecithins are a problem for anyone who is sensitive to soy. Then there is the persistent claim that most gum manufacturers dust their conveyor belts with wheat flour, to prevent the gum from sticking. Probably, many of them use corn flour, instead, but it's almost impossible to track down the details on issues such as this. I just don't chew gum, anymore.
That said, Trident states on their website that all their products are gluten-free, and Glee gum not only makes that claim, but also includes a link that will allow you to buy a kit that you can use to make your own gum, (so that you will know
exactly what's in it). Except for people sensitive to corn, the ingredients should be safe for virtually anyone else, (CONFECTIONER’S SUGAR (SUGAR, CORN STARCH), CHEWING GUM BASE, CORN SYRUP, NATURAL CINNAMON FLAVOR, NATURAL CHERRY FLAVOR).
http://www.gleegum.com/make-gum-kit.htm
Wrigley, for example, states on their website that all of their products are wheat free, but they don't mention barley or rye, which leaves me suspicious.
Tex