well of course there can be bad air in any cave. But that doesn't necessarily have anything to do with supposed treasures, it's just that caves without ventilation to outside air can develope bad air, gasses, or whatever you want to call it.
As for "treasure in caves" down in Mexico, I'm of the opinion, after chasing many such "certain leads", that they are 99.99999% superstition. I travelled all over remote sections of Durango with a guide (who brought me with him down to Mexico, because he had many "leads" back in his hometowns). Every place we went to, the minute villagers found out that Americans with metal detectors were there, they came to implore us to go hunt their yards, any cave they knew of, ruins they knew of, etc.... In each and every case, they were certain there was a treasure there. Yup, seems that every cave down there people think treasures are buried. Every old yard, every old ruin, etc.... And when you ask them "how do you know that?" It was always "someone who told someone who told someone, who told....." etc.... Or because they'd seen it in a dream, or because they saw sparkly lights in the night, or smoke coming from the mountains, blah blah blah blah.
It became quite apparent early on, that superstition of treasures down there is very deeply rooted. No amount of skeptical thinking could detract them from believing there wasn't treasures where they thought. If the detectors gave absolutely no signals in the floor of a teeny cave, well then to them, it simply meant the detector didn't go deep enough, NOT that treasure wasn't there. It became comical after awhile, and we paid no attention to any more invitations to go running around chasing stories.
