There is some evidence that SOME celiacs, who suffer from a skin disorder known as dermatitis herpetiformis should avoid skin contact with items containing gluten.
For the rest of us, the reaction occurs when the gluten is ingested, and it occurs in the small intestine. Therefore, the rule of thumb I personally use is "am I likely to ingest this?" I wouldn't put a lotion with wheat on my hands, and then eat finger food. I've also skipped on shampoos with "wheat protein" because I've been known to put my hair in my mouth. I don't however, make it a habit to check all cosmetic products, as the liklihood of ingesting mascara is pretty much nil.
That's just my take on it
Gwen