To my understanding, kryptonite is a rock that is from the planet Krypton. Superman is also from planet Krypton. Yet somehow kryptonite weakens Superman and can even kill him.

How does this work? Why exactly does kryptonite hurt him? Isn't his entire home planet made of kryptonite?


5 Answers 5


Kryptonite is a transuranic element or compound (we are never told which for certain) whose inherent radioactivity inhibits the absorption of high-energy solar radiation which Kryptonians use to power their feats of superhuman ability.


  • Not only does it prevent the further absorption of solar energy, it displaces, painfully, said solar energy with kryptonite radiation causing the immediate loss of a Kryptonian's superhuman abilities within seconds and can, depending on the purity and exposure length, lead to the death of a Kryptonian by a form of "radiation poisoning".

  • A nice analogy (promoted by AncientSwordRage) in a fashion similar to "carbon monoxide poisoning" where carbon monoxide molecules are being taken up by blood's hemoglobin instead of the normal Oxygen molecules. The CO is displacing the O2 molecules but not providing any oxygen necessary for life. With sufficient displacement of O2 molecules a person can die.

  • DC has made no official "scientific" rationalization as to HOW Kryptonite works. Over the decades, we are given a variety of reasons it works, but just vague enough we cannot be exact on the process within his cellular activity.


  • Though Kryptonite first appeared on a radio broadcast in 1943 and made its first non-green appearance in 1949’s Superman #61, we would not actually see the signature GREEN Kryptonite until 1951 in Action Comics #161.

enter image description here

  • Kryptonite's origins vary but most describe their creation at the core of the planet Krypton and were in some continuities responsible for the explosion and destruction of that world. Many pieces arrive on Earth because they traveled near the space-ship Jor-El sent baby Kal-El to Earth in. Other pieces were thought to arrive later.

  • Most depictions indicate it was only the core of the planet which was comprised of Kryptonite, though some of the earlier ones indicated any piece of Krypton that came to Earth was considered Kryptonite.

enter image description here

  • Kryptonite's origins vary depending on the continuity from which it appears in. In the Silver Age, kryptonite came in a variety of colors and each color had specific affects which were caused by exposures to different radiations, natural phenomena or scientific experimentation.

  • In almost all known continuities it is Green Kryptonite which has proven to be lethal to Kryptonians who have been exposed to its radiation. Green Kryptonite was lethal to any Kryptonian from the same universe the Kryptonite was derived from.

enter image description here

  • This fact was discovered by Post-Crisis Superman when he was forced to execute the Phantom Zone villains of another Universe after they had killed everyone on Earth. Post-Crisis Superman was immune to green Kryptonite from their universe and was unaffected by its radiations. (See SE Article: In comics how many people have been killed by Superman?)


  • Several of Superman's foes use Kryptonite as part of their arsenal of weapons including Lex Luthor, who wore a ring with a piece of Kryptonite embedded in the ring. Luthor wore this ring until it gave him cancer.

  • Said ring was recovered by Superman and given to Batman, as a part of a contingency plan to "stop" Superman should he ever be mind-controlled or have his free will compromised.

  • Metallo has a robotic body whose powerplant uses a hunk of Kryptonite as its power sources. Brainiac was also fond of using Kryptonite in many of his schemes including creating a body covered with the material.

  • More modern depictions of Kryptonite only show small amounts of Green Kryptonite on Earth, but some advanced science has been able to duplicate the signature radiation making it capable of being used as a weapon against Superman.

  • As an aside, the Green Lantern's ring is also able to replicate the signature of a piece of Green Kryptonite potentially making them capable of defeating Superman, if necessary.

  • Im wondering if the radiation is more a vacuum to supermans stored solar energy, then it is a blocker. Since he feels "drained" every time he's around it.
    – Virusboy
    Commented Feb 3, 2015 at 1:30
  • Exactly. The Kryptonite "pushes" out Superman's stored energy and replaces it with poisonous radiation he cannot process! Commented Feb 3, 2015 at 1:58
  • When you mentioned it 'inhibits absorption' it made me think of how ethanol (makes you drunk) inhibits the uptake of methanol (makes you blind). Or carbon monoxide being absorbed instead our oxygen by haemoglobin. Perhaps a similar analogy would help your already very good answer?
    – AncientSwordRage
    Commented Feb 3, 2015 at 14:32
  • I asked this question hoping to get an answer from specifically you, @Thaddeus. You rocked it again.
    – LCIII
    Commented Feb 3, 2015 at 18:29
  • So, it basically sucks the sunlight out of him?
    – Mast
    Commented Feb 4, 2015 at 12:42

No, Krypton was not made of Kryptonite - at least, not initially.

Kryptonite is a radioactive mineral from Krypton. The most common form is Green Kryptonite, but it comes in other forms, including Red Kryptonite, which has unusual temporary effects on Kryptonians, but only works once, and Gold Kryptonite, which would permanently remove Superman's powers.

image from Smallville wiki

Depending on the era, either Kryptonite was created by the explosion of Krypton, or it was found in the core of Krypton, and was released when the planet exploded.

The radiation from Green Kryptonite is poisonous to Kryptonians, causing weakness (removal of super-powers) and effects similar to radiation poisoning in humans. It's not quite the same, because Kryptonians recover very quickly when the radiation source is removed.

Reference information here: http://smallville.wikia.com/wiki/Kryptonite

  • 7
    If Kryptonite is radioactive, is it also lethal to humans then?
    – flq
    Commented Feb 2, 2015 at 14:52
  • 28
    @flq It is, although not immediately. Lex Luthor got cancer from all the time he spent working with Kryptonite.
    – Mihai
    Commented Feb 2, 2015 at 15:25
  • 3
    This great answer would be made better with some sources/screenshots.
    – LCIII
    Commented Feb 2, 2015 at 16:48
  • 2
    And don't forget the synthetic cryptonite from the Superman III movie which turns Superman evil.
    – Philipp
    Commented Feb 2, 2015 at 17:37
  • 17
    @Philipp Everyone should forget everything from the Superman III and IV movies. Everything.
    – user31178
    Commented Feb 2, 2015 at 19:22

You're Earthling, but lots of Earth-based rocks can hurt you (Radioactive ores).

Second, Kryptonite (green one) wasn't found on Krypton. It was produced during explosion of Krypton.

Superman (and, Kryptonians) has superpowers on Earth because of our yellow Sun (Krypton's Sun was red). Kryptonite blocks that ability. Also, its radiation is poisonous to Kryptonians which can kill them (although, I have read comics in which Superman had developed some immunity against green Kryptonite).

  • 5
    I think the origin of Kryptonite has varied over the years - IIRC, the original story was that it was created in the explosion, but the current version is that it was in the core and was released/spread by the explosion. Commented Feb 2, 2015 at 14:24
  • 25
    Even regular Earth rock can hurt you... if someone throws it hard enough
    – Jon Story
    Commented Feb 2, 2015 at 16:42
  • @JonStory Or even if they are big enough
    – CBredlow
    Commented Feb 2, 2015 at 17:50
  • 6
    @JonStory: Wouldn't it be great if it turned out that ordinary human beings could lift tons of kryptonite effortlessly, punch through walls of it, hurl boulders of it into orbit...
    – Beta
    Commented Feb 2, 2015 at 22:47
  • 1
    Technically our sun isn't yellow. It's white and only looks yellow because Earth's atmosphere scatters blue. Commented Feb 4, 2015 at 11:34

There are various types of kryptonite, and they all have varying effects on Superman. Each type of kryptonite contains/emits different kinds of radiation. I would think this is similar to the different radioactive elements contained within the planet Earth (plutonium, uranium, cesium, etc.)

We've been told in the comic books that green kryptonite, which is deadly to Superman, comes from the core of the planet Krypton. Likewise, the core of the planet Earth is radioactive and would kill any of us.

It stands to reason that if we were to end up on another planet, with a red sun, and if our cells were to consume the red sun radiation, giving us superpowers, that pieces of the Earth's core would still kill us - even if other beings on that planet were immune to it.

BTW - nothing in the comic books or movies or television shows says that kryptonite is exactly safe for humans either. But one would imagine that the rarity of the material generally keeps it from effecting us. If they were to find a vast kryptonite mine in Starling City or Gotham, my bet is that there would probably be a pretty large "cancer cluster" among the nearby humans.

  • 1
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    – Politank-Z
    Commented Sep 15, 2017 at 3:48

In Superman the Animated series the idea is the minerals and superman's biology contain similar elements, as such his body chemistry is easily more suited to absorbing the radiation but his powers are always in state of trying to fight it off but failing. However I also believe it's psychosomatic like expecting pain like touching something cold you think will be hot. He simply never feels pain or discomfort.....seldom, so the feeling must be overwhelming. Imagine if you were 30 years old and never had a cut or stubbed your toe or ever get an inoculation or ever felt pain in any way. How do you think you'd react if after 30 years of never even knowing what pain was you accidentally cut yourself?

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