system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are some spicy foods felt in the mouth (i.e. hot sauce) and some felt in the sinuses (i.e. wasabi?
gpt
There are two different chemicals at work, capsaicin in many hot sauces/peppers, and allyl isothiocyanate in mustards (what we call wasabi is usually actually horseradish, as an aside). 

The latter is more volatile, it evaporates more readily in the mouth and travels up into the nose with air. The former tends to stay a liquid and so is less inclined to do so. However, if you've ever sneezed after taking a big hit of hot sauce, you will discover that it definitely *can* be felt in the nose if you get it there.