Fizzy drinks are created by carbonation, which involves dissolving carbon dioxide (\(\text{CO}_2\)) gas into a liquid under high pressure. This dissolved gas is responsible for the refreshing fizz and the sting or tingle experienced upon consumption. The sensation that makes a drink feel lively is actually a complex interaction between the drink’s chemistry and your nervous system, registered as irritation.
The Chemical Signal: Carbonic Acid and Pain Receptors
The stinging sensation is driven by a chemical reaction that occurs the moment the drink enters your mouth. Dissolved carbon dioxide reacts instantly with the water (\(\text{H}_2\text{O}\)) in the beverage and your saliva to form carbonic acid (\(\text{H}_2\text{CO}_3\)). The body’s sensory system interprets this rapid drop in \(\text{pH}\) as irritation.
The body perceives this mild acid not through taste buds, but through specialized nerve endings called nociceptors that detect pain and temperature changes. These nerves are concentrated on the tongue and oral mucosa, innervated by the trigeminal nerve. The gas molecules of \(\text{CO}_2\) diffuse directly into the nerve cells, where they are converted into carbonic acid, leading to a rise in acidity inside the cell.
This internal acidification activates a specific protein channel known as the Transient Receptor Potential Ankyrin 1 (\(\text{TRPA1}\)) receptor. \(\text{TRPA1}\) is a polymodal sensor that responds to noxious stimuli, including the protons released by the carbonic acid. Activating \(\text{TRPA1}\) triggers a signal that the brain registers as a pungent, stinging sensation, which is the characteristic “bite” of carbonation.
The Physical Factor: Bubble Bursting and Pressure
While the core sensation is chemical, the physical presence of bubbles adds a distinct layer to the overall experience. When the pressure is released, the dissolved \(\text{CO}_2\) rapidly escapes the liquid, forming bubbles that rise and burst against the oral tissues. This effervescence creates a mechanical stimulation that your mouth’s mechanoreceptors detect as a tactile sensation.
This physical force contributes a light, tingly, or tickling sensation that is layered on top of the chemical signal. Studies show that the bubbles themselves are not the source of the “bite,” but they play a role in intensifying the feeling. The tactile stimulation from the bubble movement activates nerves that enhance the perception of the chemical irritation caused by the carbonic acid.
Beyond Carbonation: Role of Added Acids and Sweeteners
Many commercially available carbonated beverages contain significant amounts of non-carbonation acids that exacerbate the irritation. Colas, for instance, often use phosphoric acid, while fruit-flavored drinks frequently contain citric acid to enhance flavor and act as a preservative. These added ingredients lower the drink’s \(\text{pH}\) far below that of simple carbonated water, often reaching levels between 2.0 and 3.0.
This high degree of acidity is well below the enamel’s critical \(\text{pH}\) threshold of 5.5, which significantly increases the risk of dental erosion. The intense concentration of external acid causes general irritation and burning of the oral mucosa, independent of the \(\text{CO}_2\) conversion mechanism.
The high sugar content commonly found in soft drinks also contributes to overall oral sensitivity, although indirectly. Sugar feeds the naturally occurring bacteria in the mouth, which then produce their own acids that contribute to tooth decay and inflammation. This cycle of acid production can cause existing abrasions or areas of tissue thinning to become more reactive to the acidic beverage. Even sugar-free drinks retain the highly erosive non-carbonation acids.
Why Individual Sensitivity Varies
Individual sensitivity to the stinging sensation varies noticeably due to a combination of physiological factors. One significant contributor is the condition of the teeth, as acid exposure erodes the protective layer of enamel. When enamel thins, it exposes the underlying dentin, which is composed of microscopic tubules leading directly to the tooth’s nerve endings. This exposure results in a heightened, sharp sensitivity, especially to the cold temperature and acidity of the drink.
A reduced flow of saliva, a condition known as xerostomia or dry mouth, also increases sensitivity to carbonation. Saliva acts as a natural buffer, neutralizing acids and washing them away from the oral tissues. When saliva production is insufficient, the low \(\text{pH}\) of the carbonated drink lingers on the tongue and mucosa, prolonging the acid’s irritating effects.
Differences in the nervous system itself also play a role in individual perception. The number and sensitivity of the \(\text{TRPA1}\) receptors in a person’s oral cavity can vary, meaning some people naturally have a more robust response to the chemical stimulus. Furthermore, any existing cuts, mouth sores, or inflamed gum tissue will react acutely to the acidic environment, turning a mild tingle into a distinct pain for some individuals.