Why is superman's weakness kryptonite?

Question

If kryptonite is the remains from Supermans native planet, why is it that it is his weakness?

Answer 1

The version of Superman causes K to vary. But the general reason is that the explosion that destroyed Krypton changed the chemical/radioactive properties of the surviving material.

"In Superman: The Movie, Lex Luthor describes Superman's enhanced Kryptonian physiology as being vulnerable to kryptonite's particular radioactive "signature". More recently, some issues of Superman indicate the mechanism by which green kryptonite may hurt Superman. Superman's cells absorb electromagnetic radiation from stars (like Earth's sun). Kryptonite's radioactivity interferes with this semi-photosynthetic process, driving the energy out of his cells in a painful fashion.

Long-term exposure to kryptonite is said to have the same effects on human beings as exposure to other radioactive materials; an extended storyline in the comics around 1990 involved Lex Luthor developing cancer from the kryptonite ring he kept on his finger."

The full (but somewhat limited article) can be found at Wiki.

Answer 2

In Superman home planet he didn't has 'super power' like he do on earth because of the kryptonite scattering all over the planet. Because of that whenever he's exposed with Kryptonite it'll changes him back to normal state--non super power mode. Most DC character usually has a weakness from outside/alien stuff that didn't existed on earth if you noticed. Maybe because their superpower was ridiculously 'SUPER POWER' compared to Marvel stuff..

Not sure if this the answer you're looking for though. If you want more specific/detailed answer about the effect of Kryptonite refer to the link guy above me provided.

Answer 3

For the purposes of irony.