A couple of years ago I wrote a post that explained my theory of how some allergies start. I think a person’s body can learn to react to something that is usually harmless, if it is exposed to that harmless substance during an exposure to a toxin.  The immune system learns to associate one with the other.  I searched in vain to find this theory mentioned somewhere else.

But I recently found an article on mosaicscience.com (that site is no longer active) that describes how doctors can  “teach” a patient’s immune systems to react to inert substances as if they are medications.  They give them a medication and at the same time give them a substance with a distinct taste or smell.  They are finding that later they can give just the substance and the body’s immune system will react the same as if they had received the medication.

I can’t say for sure but this sounds like it is the exact same mechanism at work.  The reason my search didn’t find this is because I was looking for the immune system learning a ‘bad’ lesson and here it is learning a useful lesson.