Ever gulped a soda too fast and felt pain, almost like it was burning your nose or throat?
There's a scientific reason for that. According to research published in the Journal of Neuroscience, the carbon dioxide that makes soda fizzy activates nociceptors—the cellular receptors that trigger the perception of pain—in the trigeminal nerve, which is the main highway for sensation in your face, nose and mouth. Specifically, carbon dioxide activates the particular nociceptors that feel the burn of flavors like wasabi, mustard and cinnamon oil.
In other words, from your body's perspective, fizz is spicy.
Neurobiologists at the University of Southern California discovered this by pouring a carbonated saline solution over trigeminal nerve cells harvested from lab mice, and identifying the presence of a particular nerve channel called TRPA1 in the cells which had the strongest reaction. (They also studied TRPV1, the channel present in nerve cells sensitive to capsaicin—the "heat" in chili peppers—but concluded that "our data argue against" a connection to fizz-induced pain.)
"Carbonation evokes two distinct sensations. It makes things sour and it also makes them burn," said lead author Emily Liman, referring to a study reported last year which showed that fizz also activates the tongue's sourness receptors.
"We have all felt that noxious tingling sensation when soda goes down your throat too fast," she added.
Mmm, sourness, "noxious tingling" and burping—anyone want a Coke?