Blueeyedgrl73, I am not sure exactly what is meant by "hidden." GF-folks have to read every label and hunt for the offenders as the word gluten will not be listed. We are very fortunate if a label says "gluten free" and mostly these products are found in speciality stores or the speciality isle at the supermarket.
There are scads of terms to watch for....and it gets disheartening. My all time favorite is "vinegar", if it does not give the source of the vinegar, then GF folks must pass that product by. Some products will say, "apple cider vinegar." Yeah! Some GF folks shop with their cell phones and will call the manufacturer right from the isle and ask their questions. It is so time-consuming, I have done that once.
There are too numerous terms to mention here, there are websites that will have the info listed.
I was diagnosed with celiac disease last year, but had been basically on a wheat free diet to help the symptoms of CFS/FMS. I was very ill. Raised the level of my diet to hunt out and eliminate the gluten and I did get better.
Many medications, OTC and prescription also have gluten in them.
Alcohol is extremely tricky. Imported or domestic. It's not just the grain-derived spirits. Fortified wines can have barley mash ferment added. Regular wines can have gluten "gum" used to seal casks or some form of gluten used during processing. And it's really difficult to get info on wine processing, not required by law to be listed or available to consumer.
And then there's beer -- unless it's a GF beer, it's off limits.
Sauces, esp. oriental sauces with "soy sauce" usually have wheat unless the sauce is specifically GF. Spice blends can be "cut" with flour or wheat starch -- celiacs are much better off with pure spices unless a blend is guaranteed GF.
Most people don't think about their makeup & HABA products, but wheat/wheat protein are increasingly used. Lipstick gets eaten. Some people also react to hair products & makeup that is simply applied, not eaten.
Other nonedibles -- some drywall spackle uses wheat ingredients & in crafts, some glues & of course traditional papier mache.
Some charcoal briquets are bound with gluten and/or wheat starch. Barbeque grills in general are easily cross-contaminated with nonGF sauces or marinades.
Some paper towels/ TP may have wheat starch glues/stiffeners used. The name-brand product manufacturers can tell you whether or not their product uses grain glue.
Which brings me to "air." There's often a minute quantity of gluten in the air we breathe. I'm talking ppb -- a very minute amt. However in some circumstances, like a bakery, or a nondedicated home kitchen, that minute amt can be enough to trigger serious reactions in some very sensitive gluten intolerant folks. If you've ever spent time observing operations in a large commercial kitchen, or even seen what happens when someone makes bread with a KitchenAid type mixer, it's easy to see how gluten becomes airborne.
Celiac disease is more common among professional bakers, who have regular airborne gluten exposure, than it is in the general population. While traditional medical dogma is that gluten must be ingested to cause intestinal damage, there's been some intriguing research done the last few years on the immune/autoimmune response generated by the body when gluten is inhaled.
Another route of airborne gluten exposure is through raw grain during harvest/seeding seasons, as well as animal feed, including some pet food.