Most spicy foods contain a chemical called capsaicin, which is the active component found in chilli peppers. Capsaicin is an irritant for humans and most other mammals, and produces a burning sensation in any tissue which it comes into contact with. It triggers a response in goblet cells whose function is to secrete mucus and this is why you get a runny nose. However, there is evidence to suggest that it is possible to build up a tolerance to the irritating effects of capsaicin. This could be the perfect excuse to visit the curry house more often!
There is a widely held belief that water will help but capsaicin is not soluble in water, therefore the burning sensation and runny nose will continue. Cold milk has been found to provide the most effective relief as it contains a protein called casein, which has been found to detach the capsaicin from the nerve receptors.