It is. Why do you think people are obsessed with antioxidants? Oxygen is what causes ageing and slowly, over time, kills your cells; we've evolved to use it for energy and be fairly resistant to it, but it's still poisonous.
... oh, right, stupid answer. Well, try spending a week in a vacuum and see if you feel any better.
Why isn't Reggie Fils-Aime playable in Smash?