“Is Superman giving people cancer whenever he uses his X-ray vision?” – Jason G.

Superman has a crazy amount of powers. Some of them pretty much set the standard for superheroes: super strength, super speed, flight, yadda yadda yadda. Others are a little more weird and sometimes useless: super smell, freeze breath, and the ability to turn back time by flying around the Earth really fast… or something.

Superman’s X-ray vision, while not really a superhero staple, is pretty damn useful. He can find hidden weapons, people trapped in buildings, and provide a quick and painless colonoscopy.

But let’s get to the meat of the matter. X-rays can indeed cause cancer in humans. Obviously, a high dose of X-ray radiation over a short period of time can cause radiation sickness, and lower doses, even those that are used in everyday medicine can increase the risk of cancer (source)

That’s because X-rays are a type of ionizing radiation, which is radiation that has enough energy to knock electrons out of atoms. Now if this were to happen to a bunch of atoms in your DNA, that’s a problem. The probability of radiation induced cancer increases by approximately 5.5% per Sievert of ionizing radiation (source). How many Sieverts you get depends on the type of X-ray procedure you undergo, with the highest being those done around the spine and the hips (source).

But don’t get too worried, because most of the cancers resulting from X-ray use are in the case of several repeated X-ray and CT scan procedures. So, unless you’re living your life in an X-ray machine, you really should be fine. Besides, the medical benefits of X-rays outweigh the minor risks. Otherwise, how would they diagnose your Charlie Horse, or the Water in Your Knee?

If Superman was really blasting X-rays everywhere in relatively concentrated doses (as they’re essentially beams from his eyes), yes, we’d be in trouble. If he wanted to know if you were carrying a concealed weapon, you’d probably die of lung cancer.

But this idea about his ‘X-ray vision’ is based on a fundamental misunderstanding on how medical X-rays work. The common ‘X-ray’ procedures doctors use to see our bones is more properly known as Radiography. The process of getting one of those cool skeleton pics is simple, your body is zapped with a bunch of X-rays, and, given the difference in densities of tissue and bone, the X-rays are absorbed by your bone while they pass through your tissue and are captured by film and/or a detector behind you. When you’re done, you get the negative or “shadow” that was projected onto the detector.

Superman, on the other hand, is just staring intensely at things. If he was emitting X-rays from his eyes, it would have the same effect as an X-ray, but there would be no detector on the other side to pick it up and create the negative.

Furthermore, sometimes Superman can just see through walls and see the rooms and stuff inside, which wouldn’t be possible with real X-rays. So the conclusion can be drawn that Superman’s ‘X-ray’ vision doesn’t use real X-rays at all! It’s just flagrant false advertising.

So how does Superman do it? Well, I don’t know for sure, because I don’t think DC comics has ever addressed it in canon. But if I were to hazard a guess, I would say that Superman’s Kryptonian eyes are highly advanced versions of our eyes. This should enable him to see every type of electromagnetic radiation under the (yellow) sun. From Extremely Low Frequency (ELF) radiation all the way up to Gamma radiation.

But I suppose seeing everything all the time can be tiring, so there might be a biological filter in place that he can control by thought alone, allowing Superman to limit what radiation he picks up. Basically like internal sunglasses.

Now, you may not notice, but every single thing in the universe (you, me and Lex Luthor included) gives off electromagnetic radiation. They’re low amounts, but they’re still there. Perhaps Superman can attune his eyes to pick up only the emitted radiation he wants to see, like that given off by a gun or a bomb or the Legion of Doom stronghold. So if you’re holding a gun under your jacket, Superman’s super eyes can selectively pick up the radiation given off by the gun, but not your clothes. This lets him see exactly what you’re packing… in more ways than one. *wink*

That is, unless you’re wearing lead. Superman can’t see through that, so I assume his Kryptonian eyes lack that specific filter.

So there you have it. Superman’s X-ray vision would never really give us cancer, because it doesn’t make sense for him to shoot real X-rays out of his eyes at all.

Now, if he shot gamma rays out of his eyes, that would be a different story.

If you have a ridiculous sci-fi question you’d like me to attempt to answer with real science, please e-mail me at NairForceOne@Gmail.Com, with “[BACK OF THE ENVELOPE]” in your subject line.