I'm currently working on making some changes to an original race of aliens that are very humanoid, as well as the mixed race children they had with Earthlings. For some variety, I was hoping to make it that these aliens breathed something other than oxygen, but I'm having a great deal of trouble figuring out what sort of changes that might make to them physically/if it would really be possible. I've read enough to know that hydrogen would be a bad choice, which is disappointing since it could be distilled from water. They'd probably blow themselves up before they could get it into their lungs. XD So, I thought maybe nitrogen. What would it be like if humanoid creatures breathed nitrogen? The alien body processes do not need to be 100% human-like, but I'd rather not have major changes to their physical appearance. Is it at all possible than an inert gas be used for respiration?
Also, would it be possible that the mixed race children be able to breathe both oxygen and nitrogen? Like, their bodies would start off with oxygen and if the oxygen was cut off somehow, they would automatically switch to breathing nitrogen? Or would this result in some sort of explosive reaction I'm not aware of? (Science was never my strong subject.)
Used searches like, "What if we breathed nitrogen?" which came up with links describing how we would die if all we had in the air around us was nitrogen since we breathe oxygen. Not at all helpful, in other words.