You have to be really careful when looking for gluten-free facial products for several reasons. Facial skin is extremely sensitive, so you'll want to take plenty of precaution with the cleansers you use. Because facial masks, like exfoliating sponges, are deep-cleaning and penetrate the skin to extract built-up oil and grime from your pores, a bad reaction to masks that contain gluten could be extremely uncomfortable. Also, facial masks are applied close to the mouth, a dangerous area for people who can't consume foods that contain gluten. People with celiac disease and dermatitis herpetiformis can have extremely negative reactions to consuming even trace amounts of the protein.
Luckily, there are several gluten-free facial masks available, and if you look hard enough, you'll most likely be able to find one at your local store. However, as is the case with most skin cleansing products, not all gluten-free facial masks advertise themselves as such, so be sure to check the ingredients. If you're still not sure, don't be afraid to contact the manufacturer.