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University of California at Davis researchers say many of the substances we enjoy consuming actually trigger pain, and argue that pain makes up an important component of some flavors. 

In a study published last month in the Journal of Neurophysiology, neurophysiologist Earl Carstens and food scientist Michael O'Mahony compared the effects on nerve activity of capsaicin, the substance that makes chilis hot, and nicotine. They found that when dropped on the tongue of rats, both trigger the firing of trigeminal nerves, which transmit pain to the brain. 

Carbonated drinks also cause painful sensations on the tongue, according to neurophysiologist Earl Carstens, because the carbon dioxide in the bubbles forms carbonic acid. 

“If you stick your tongue in carbonated water for a few seconds, that gets painful,” Carstens said. 

Other flavors with painful effects include vinegar, salt, black pepper, mustard and horseradish. 

“Humans have to learn to like these irritants, because they are all activating pain pathways,” Carstens noted. 

Not all of these irritating flavors and substances act in the same way, however.  

The burn of a spicy meal will actually continue to increase as long as you keep eating it continuously, but will be reduced if you pause between bites. Nicotine, on the other hand, desensitizes nerves almost immediately. 

The research is part of a body of work which aims to understand how the brain interprets flavors, and what factors affect taste.