In the first season episode "The Erlenmeyer Flask", Mulder and Scully come across an orange substance labelled "Purity Control". After having it analyzed, they learn that it contains alien genetic material. From the context of this episode, it seems to have some role in the human/alien hybrid experiments. It turns up later in "Red Museum", where it was apparently being injected into people (and animals) as part of some experiment. The wiki entry for Purity Control seems to indicate that its purpose was specifically to "create alien/human hybrids". This hybridization program was apparently an agreement made between a secret government syndicate and the aliens so that humanity would survive their eventual colonization, albeit as slaves.

However, in later episodes, it seems that the mass hybridization program, as planned, would be carried out infecting everyone with an alien virus (the black oil) carried by bees. We also learn that some of the members of the government syndicate were secretly attempting to develop a vaccine to resist the alien virus and stop the colonization. Every time that we see this vaccine, it is an orange liquid that looks exactly like Purity Control.

To complicate things further, we learn (years later) that the black oil/alien virus is actually called "Purity". Now whether this was a neat bit of foresight or just retconning is something that only the writers know. :)

So I guess I'm confused. The name "Purity Control" would indicate that it is a vaccine, but in the early episodes, it seems to be the agent by which the hybridization and colonization would be carried out.

Does anyone recall an episode where this was addressed?

  • It's been a LONG time since I last watched the X-Files (and things weren't exactly "spelled out" in the show to begin with.) IIRC, there were at least two different alien factions involved. The greys (who I think were already infected by the black oil) trying to colonize/enslave mankind, and another race (never properly revealed, but may have been uninfected greys in a resistance movement) who sent human clone assassins to undermine the first group. The second race may well have developed "Purity Control" as a means of expulsing the black oil from a host body as part of the fight.
    – Steve-O
    Commented Nov 18, 2016 at 14:12

1 Answer 1


Purity is an alien virus used by the colonists to take over other planets. The virus infects indigenous lifeforms and hijacks their cellular machinery to produce more alien colonists. Back in the 1970s a group of humans known as the Syndicate (Bill Mulder, The Smoking Man, et al.) found out about the alien plot to begin colonization of Earth in the year 2012 (the distant future!). Realizing the severity of the situation they threatened to make the surface of the Earth uninhabitable by bombing with nuclear weapons. Using this leverage they were able to come to a compromise with the alien colonists. The colonists would give them alien DNA to help The Syndicate develop an alien human hybrid, which would be able to survive the coming colonization. In return The Syndicate promised to pave the way for the coming colonization. Unbeknownst to the alien colonists The Syndicate had a secret plan. The entire time they supposed to be helping the colonists they were using the alien DNA giving to them to develop a vaccine against the Purity virus. They called this vaccine Purity Control. Their plan was to distribute the vaccine to all of humanity, saving the world from alien colonization.

  • 2
    This is a good, concise summary of the "X-Files" mythology (seriously). It also largely just restates my question. :) My question was specifically why "Purity Control" (the orange liquid) seems to be the agent of hybridization in the early seasons, then becomes a vaccine against it in later ones. I mean, look at what happens in the first movie: one dose of the vaccine injected into Scully pretty much destroys the entire underground Antarctic alien base. Is there an episode that addresses this, or was it a goof/retconning? Commented Apr 17, 2017 at 19:46
  • 1
    Some vaccines are "watered-down" versions of a virus that help kick-in the auto-immune system. Flu-shots, for instance. Commented Aug 29, 2017 at 5:00

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.