After reading this question, I commented an observation: the strongest acids we know of from Earth elements contain fluorine, such as fluoroantimonic acid (pH -23) and fluoroboric acid (pH -16) owing to the insane reactivity of F atoms. Drops of these acids will disintegrate skin to the bone before your eyes (search YouTube.) Metals, too.

Whatever the Xenos eat from man-made settlements (USCSS Nostromo, Hadley's Hope, Fiorina 161, etc.), it must be rich in fluorine because matter cannot be created magically.

Where could Xenos get "F atoms" to make their acid in such quantities in the Aliens universe?

  • Non-canon afaik but: there are fringe theories that terrestrial organisms transmute elements, not just split compounds but actual nuclear changes which we don't know how to perform artificially without using, for example, a radioactive source or a particle accelerator. Xenos certainly display very strange biology, growing many fold in hours, etc. Why could the creatures not be able to transmute elements into other elements, especially because this might really happen on Earth anyway?
    – releseabe
    Oct 13, 2022 at 3:21
  • @releseabe That's fair enough, but my goodness gracious does something like transmutation (alchemy) take an unimaginable energy source to pull off (from Earth elements)! Now if early on the burstlings ate some Plutonium....
    – Drakes
    Oct 13, 2022 at 3:42
  • My basic point is, the Xeno does some things far less plausible than, at least from wonders that occur in science fiction, forcing two atoms together. Fusion and fission really do happen; that some biomechanical weapon created by an alien race more advanced than us can cause "cold" fusion scarcely qualifies as a wonder. It reminds me of an old Outer Limits where the episode's "science fiction" was a pacemaker, in those days iirc.
    – releseabe
    Oct 13, 2022 at 3:50
  • 3
    Geologist here. You are right, it probably is not possible to get enough fluorine out of human beings to account for the acid in the aliens, considering that most fluorine compounds are toxic to humans. There's a little bit in bones and teeth. There's also a little fluorine in some minerals, but the aliens would have to process a lot of rock and I haven't see them doing that in the films. As for transmutation, you are right again -- that trick is far more dubious than eating rock; it would take too much energy. So just sit back, eat your popcorn, and enjoy the show with suspended disbelief. Oct 13, 2022 at 4:02
  • Another thought is, why couldn't the basic source of power be nuclear? It would not need to eat to obtain energy from chemical compounds, but just use some very energetic stuff like radium for power and then obtain materials to increase in size and complexity from the environment, transmuting elements as needed. Some mumbo-jumbo here, but more plausible than, for example, traveling faster than light -- way more plausible than that.
    – releseabe
    Oct 13, 2022 at 4:09

1 Answer 1


There is no reason to think that the acid in Xenomorph blood has to contain significant quantities of fluorine. There are many strong acids, plenty of which contain nothing other than commonly occurring organic elements (C, H, O, N, Cl, S, P, etc.)—for example, sulfuric acid, perchloric acid, and p-toluenesulfonic acid.

From a practical viewpoint, there is not much difference in reactivity between different strong acids under most circumstances. All strong acids are completely ionized in water solutions, producing hydronium ions that react with whatever they come into contact with. What distinguishes superacids is only their ability to protonate other strong acids, while the reactivity of various strong acids with pH-neutral materials are not that different.

The action of the acid seen in Alien appears to be typical strong acid behavior, dissolving plastic or metal. There is nothing to indicate that a superacid is involved.

Captain Dallas actually overreacts to the appearance of the acid, thinking it will "eat through the hull," when in fact it makes small holes through a couple of internal decks before being exhausted. The practical visual effect of the liquid blood dissolving the solid floors could be reproduced with any of multiple strong acids. They probably actually used an acid that was readily available commercially, such as sulfuric, nitric, or hydrochloric. Moreover, in the Aliens vs. Predator: Requiem official documentary "Science of the Alien," it was suggested that the acid was sulfuric, which is basically consistent with what is seen in films.

  • “There is no reason to think that the acid in Xenomorph blood has to contain significant quantities of fluorine.” <— the reason posted in my question. Also, “This superacid that can be in excess of 10^15 times stronger than pure sulfuric acid”.
    – Drakes
    Oct 20, 2022 at 21:21

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