I just saw a news article about a woman with Aquagenic Urticaria which basically means she produces antibodies against H2O molecules which causes very bad symptoms if she touches or drinks water.

We're told you can't be allergic to oxygen, glucose, salt etc because they're too small and simple. So why is H2O an antigen?

NCBI source - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3276800/

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    Please don't crosspost: Is the H2O molecule an antigen like this article states? – LаngLаngС Mar 22 '19 at 15:31
  • You've asked this question or nearly identical questions repeatedly on multiple SE sites, and you've received several good answers. I think it would be a good idea to accept those answers and consider the question answered. – Carey Gregory Mar 22 '19 at 17:59
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    @CareyGregory it might be a good idea to pass this up the chain. This user is attempting to get out of a 10 year suspension by creating a new account. Previous name was Willy150, which similarly, was created to get out of a suspension. I don't have the original user name at hand. – De Novo Mar 22 '19 at 18:02
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    @CareyGregory details here – De Novo Mar 22 '19 at 18:07
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    @DeNovo Handled. – Carey Gregory Mar 22 '19 at 18:14

The pathogenesis behind Aquagenic Urticaria isn't definitively known - and the extreme rarity of the condition makes studying it difficult (only ~100 cases published!)

It does appear to be an allergic-type response - as shown in the linked article from your question the wheals are formed when histamine is released and AU appears to respond to antihistamine treatment in most cases.

One theory (Czarnetzki et al ) is that the patient isn't having an allergic reaction to the water itself but rather a water-soluble antigen present at the epidermal layer - and that when the antigen is dissolved in the water it then diffuses through the epidermal layer causing the mast cells to release histamine and produce the wheals.

However that is probably not the full story - since there have been reported cases where there was no signs of a histamine response and treating with antihistamines proved ineffective (Luong et al)

So to summarize - no definitive mechanism as been determined, but it's probably not a case of simply being allergic to H2O molecules.

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    How does the water soluble antigen explain people who also cannot drink water because they have a reaction in their throat? – Willy A Mar 22 '19 at 15:23
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    @WillyA plenty of skin in the mouth and it's vicinity (for example the lips) for that to come from. But it's far from a perfect theory by any means, about all everyone can agree on is that it's not a straight allergic response to water molecules - an IgE mediated allergy to H20 would be far more catastrophic since we have rather a lot of it inside our bodies. – motosubatsu Mar 22 '19 at 15:35
  • Within this soluble antigen theory, is an assumption that the antigen is a not an essential nutrient required? In other words, can allergy occur from an essential nutrient? – 3495 Mar 22 '19 at 15:38
  • Couldn't this theory be tested by examining wheals from saline? Wouldn't injecting a hypertonic solution inhibit dissolving the antigen? – 3495 Mar 22 '19 at 15:40
  • @fredsbend I believe the suggestion was that it was a component of the epidermis itself that acted as the antigen. As to whether it's possible to be allergic to an essential nutrient - no idea, I'd imagine you probably wouldn't live very long were you to have such an allergy though! – motosubatsu Mar 22 '19 at 15:45

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