What is it about spicy food, that clears out your sinuses and makes your nose run?
Capsaicin irritates your mucous membranes; this irritation stimulates their primary function: to produce mucous.
When it first forms, mucous is runny.
Spicy food is spicy because of a chemical called capsaicin. Capsaicin is an irritant, so it causes inflammation. And inflammation in your nose and sinuses causes them to release water to “flush” whatever irritant is inside them out. In the process, it also flushes out the mucus that naturally covers your nose and sinuses, clearing them out.