Question about Kryptonite

[m0nstaLulz]

So why would something from Superman's home planet be poisonous to him?

[MykeHavoc]

Because it's been irradiated from the destruction of Krypton, it's journey through space, and it's arrival on Earth. You could also theorize that much like Superman himself, the newly exposed elements, such as our unique atmosphere, could play a part in the eventual state it ends up in. Plus, yah know... comics, man. Suspend disbelief for the pseudo-science and just enjoy the stories.

[Jon Clark]

Also how many naturally occurring things on Earth are deadly to humans? It's not like you couldn't find a dozen poisons from Earth to kill a human being even before you factor in what those chemicals might become after being exposed to forces that rip a planey apart.

[Slaughter]

My favorite explanation for the ol' K rocks is that they are like super-fast radiation poisoning/energy overload for kryptonians, because the energy they emit activate the same solar energy reception/catalyst but in a way that hurts Kryptonians instead of powering them.

There's also a weird fan theory that Kryptonite actually overloads kryptonians with power (post Return of Superman comes to mind), and being repeatedly exposed to Kryptonite makes kryptonians gradually increase in power.