After eating spicy food, why does breathing-in cool my mouth, but breathing-out burns it more?
It would have to do with the fact that the air you breathe in is cooler than your mouth/lips, and the air you breathe out is warmer.
most spicy foods work by activating a receptor that reflects heat. Imagine if there is a thumb print machine and the thumb that opens it is heat, the spicy food has capsaicin which also has the same thumb print. Basically activating the sensor. When you breath in, the air in ambient which your body is used to. But when you breath out it comes out around 30 degrees C. Which is going to trigger the censor which is partially opened by spicy foods.
The air you breathe in is cooler than the air you breathe out (usually). So when you breathe out you’re blowing hot air, which obviously is not as good as getting cold air.