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.
https://www.thefreelibrary.com/JUST+ONE+CUP+OF+WATER+COULD+KILL+LITTLE+HEIDI%3B+Girl's+deadly+allergy…-a061152595
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 - Aquagenic Urticaria: A Report of Two Cases - PMC