The proteins that make up gluten are found in wheat, barley, and rye. A protein in oats is so similar that it can also trigger an immune response in a person with coeliac disease.

Besides the obvious flours and starches that come from glutenous grains, there are other baking and cooking products contain gluten. Things like simple and complex sugars made from starch; malted and sugar syrups; products that are "grown" in gluten bases; and the list goes on ..

With icing and frosting ingredients, it is ingredients like Dextrin, Maltodextrin and Dextrose may be sourced from wheat or barley .. or the manufacturing plant may be cross-contaminated with flour, starch sugars, etc ...

1. Powdered sugar contains a component of starch .. in the US, it is usually cornstarch BUT not always .. imported products may contain wheat starch.
2. the main ingredient of confectioner's sugar is sugar but not always sucrose ..

Things to think about ..

Great onfo, auzzie...obviously my knowledge of this issue is really limited. Good thing I don't need to cook/bake gluten-free. This makes me wonder about how gluten-free baked goods really are. I believe this is the first time I've read anything about sugars possibly containing gluten.