Have you ever read the ingredients on your makeup?
I do, every single time I buy some. There are a few makeup companies that only produce gluten-free makeup, and those are really the ones I trust anymore.
It may not seem like a big deal, but my skin reacts to even trace amounts of gluten, and any gluten in lip products can be downright dangerous. So I buy gluten-free lip balm, foundation, lipstick, mascara, everything. It's just safer that way.