Why does spicy food make our nose run?

Ever wonder why your nose starts running when you eat something spicy? The culprit is capsaicin, a chemical compound found in chili peppers. When you consume spicy food, capsaicin molecules bind to specific receptor nerve endings located in your mouth and nasal passages.

These receptors usually respond to actual heat. Capsaicin triggers these receptors, even if the food isn't particularly hot. The nerves react as if they are sensing a burning sensation, creating a false alarm. This, in turn, sets off a protective reaction in the nasal lining called neurogenic inflammation.

During neurogenic inflammation, the nerves release signaling molecules. These molecules cause blood vessels in the nose to relax and widen, increasing blood flow. This stimulates the mucus-producing glands in the nose, causing them to release watery mucus. The increased mucus production is designed to dilute, cool, and flush away the perceived irritant.

Interestingly, water isn't very effective at stopping the reaction because capsaicin is an oily substance and does not dissolve well in water. Milk, however, works better because it contains casein, a protein that surrounds oily molecules like capsaicin, helping to wash them away. Sugar can also help by interacting with capsaicin and reducing its ability to bind to the nerve receptors.