Why does spicy food make our nose run?

When we eat spicy food containing chillies, a substance in them called capsaicin binds to receptors on the nerve endings in our mouth and nose. These receptors work like sensors. When a specific molecule attaches to them, they send a signal that triggers a response.

Capsaicin attaches to receptors that normally react to actual heat. However, even when the food isn’t hot, the nerves respond as if it was, creating a false alarm. This causes the nasal lining to initiate a protective process called neurogenic inflammation. 

As part of this process, the nerves release signalling molecules that relax nearby blood vessels. This boosts blood flow and encourages the mucus-producing glands in the nose to release watery mucus, which makes our nose run. The mucus helps to dilute, cool, and wash away the irritant.

Capsaicin is oily and doesn’t dissolve in water, which is why drinking water does little to help. Milk works better because it contains casein, a protein that wraps around oily molecules like capsaicin and helps wash them away. Sugar also interacts with capsaicin and reduces its ability to cling to nerve receptors.

S.P. Kirtik Raj is interning with The Hindu.