The distinctive spiciness of chili peppers comes from the chemical capsaicin, which causes a burning sensation when in contact with bodily tissues.
Capsicum plants produce capsaicin in their fruits, which are chili peppers, to fend off possibly hungry mammals.
What does this have to do with your runny nose? Capsaicin irritates mucous membranes the linings that protect your lungs and various body openings and cavities from various infectious agents such as fungi, bacteria and viruses.
Mucous membranes in the nose produce nasal mucus, known also as snot, which traps allergens, airborne dust and other undesirables, keeping them out of the respiratory system. The more irritated the nasal membranes become, the more mucus they produce as a defense.
If you’re looking for the best way to beat the heat, reach for milk. Milk quenches capsaicin’s fire quite effectively.
If there’s no milk handy, try a 10 percent solution of sugar in a cold glass of water.