system
Given the following post, respond as if you're commenting on Reddit:
human
Why does it hurt to drink cold water after I have a mint or use mouthwash?
gpt
One active ingredient in many brands of mouthwash and, found naturally in peppermint is the Menthol essential oil. Menthol is noted for its chemical ability to trigger the TRPM8 receptor on the skin; this receptor is responsible for the cool feeling on the skin.

Similarly, Capsaicin is the the chemical in hot peppers that is responsible for aggregating a sensation of heat. 

Both of these chemicals send signals to the brain to emulate the feeling of cool or warm without actually changing the temperature. This can cause blood to flow to the affected area; this is why icy hot becomes effective.