How would an immune system 'allergic' to plain water would 'know' if someone just drunk plain water?

[RichardFWhite]

I read some people have a bad immune reaction if they drink plain water (tap, distilled, sparkling water, etc) and I read about a girl who could not drink even a sip of plain water because it'd send her into anaphylaxis, but if they drink tea, milk or cola they have little to no reaction, so how would their immune cells 'know' if they just drunk plain water? The water molecules floating around in a glass of milk (>90% water) are still water molecules, right? Why would the water/liquid in the body be seen as ''OK'' but plain water is ''not okay'' in these people's immune system cells?

[Sensei]

More correctly it is called "Aquagenic urticaria". Reading this article will explain couple things to you:

https://en.wikipedia.org/wiki/Aquagenic_urticaria

 

[RichardFWhite]

1 minute ago, Sensei said:

More correctly it is called "Aquagenic urticaria". Reading this article will explain couple things to you:

https://en.wikipedia.org/wiki/Aquagenic_urticaria

 

The Wikipedia article doesn't really do the condition justice, since there are cases where people cannot drink water either, and none of the explanations in the Wiki article explain why people with this condition cannot drink plain water, but they can drink milk for example.

 

Here is a severe case of the condition. Note that it is mentioned she drunk a mouthful of water by mistake, and then went into shock (that was treated with adrenaline). https://www.thefreelibrary.com/JUST+ONE+CUP+OF+WATER+COULD+KILL+LITTLE+HEIDI%3B+Girl's+deadly+allergy...-a061152595

Edited August 15, 2019 by RichardFWhite

[Sensei]

"Like others with the condition, Rachel drinks a lot of milk, since the reaction isn’t as bad as with water. "

http://www.bbc.com/future/story/20160915-the-woman-who-is-allergic-to-water

It means there is still reaction to water molecules in milk. Simply not as severe as with plain water.

[StringJunky]

Maybe the concentration is the determining factor.  With milk, the water is diluted by the other constituents, so the immune system may not adversely react. Seems odd talking about diluting water but there it is.

Edited August 15, 2019 by StringJunky

[RichardFWhite]

31 minutes ago, StringJunky said:

Maybe the concentration is the determining factor.  With milk, the water is diluted by the other constituents, so the immune system may not adversely react. Seems odd talking about diluting water but there it is.

would this mean they have immune cells sensitive to high osmotic pressure?

[John Cuthber]

"How would an immune system 'allergic' to plain water would 'know' if someone just drunk plain water?"
Very good question.

The answer is that it could't.

That's how we know that nobody is (or can be) allergic to water.

Obviously, that leads to a different question; "What are these people suffering from?".

 

Has anyone positively ruled out a psychological origin?