I know you wrote H and O, and not H2 and O2, but I'm going to assume the gas forms because those two substances pretty much cannot exist in their pure forms

And for those, O2 is necessary for our life, and H2 is non-toxic, it's just very flammable. So I don't know if the comparison fully works

Of course, you're right if you mean pure H and pure O, but, again, they will immediately combine to form a new substance