I play paintball, if you wear a mask, they're only set for 340 FPS, so if you go to an airsoft field pinging 400-500, say good by to those eyeballs of yours, unless you buy one and stress test it. To my knowledge, it's a bad Idea, but I could be wrong.
To an addition to what Gunny said, you can buy special fog proof wax, there's a guy on youtube named Dre_Wolf, or something of the sorts, he has guide on that stuff, there are masks that have fans as well. Most masks aren't aqua proof, so if you sweat, it'll get all over your goggles, which can severely disorient your sight, especially if you're hopped into a building and being supressed, you'll sweat like a pig.
In my opinion (which is what I'm about to do seeing that I'm fresh to the sport) just get a pair o'these:
http://www.armyissue.com/store/index...c-goggles.html