Allergy testing and H2O

The newest round of tests for my itchiness are allergy tests. I had the environmental test two weeks ago. They pricked me with 14 different allergens. Turns out I'm allergic to cats, tree pollen and dust mites. Now I'm in the midst of a chemical test where they put patches of the chemicals most commonly used in everyday cleaners and shampoos and stuff like that on your back and leave them there for 2-3 days. We'll see how that goes.

This morning I showed the patches to the boys I nanny. The oldest one (he's 6) was super interested and asked lots of questions. And when I told him the patches were bothering me he very sweetly offered to let me smell the cleaners in his house and he would watch to see if I sneezed. Later on he asked me if I was allergic to H2O. I said no and then he asked if there is carbon dioxide in H2O. Instead of answering him I asked him some questions of my own:
Me: "What does the H stand for?"
6-year-old: "Hydrogen."
Me: "Right. And what does the O stand for?"
6-year-old: "Oxygen."
Me: "Right. So is there carbon dioxide in water?"
6-year-old: "No, but there are two Oxygen atoms and one Hydrogen atom."
Me: "Umm ... Right."
He's too smart for me. :)