Carbon Dioxide in Soda: Where Does It Go If You Can't Burp?

The moment you open a can, there is a ‘hiss.’ That sound is, in fact, an escape. It is the sound of carbon dioxide molecules, which were forcibly trapped in liquid just seconds ago, suddenly becoming free.

We usually only think this far: drink, burp, done. However, a single can typically contains 2~3g of carbon dioxide. It doesn’t all come out in one burp. So, where does the rest go?

Carbon dioxide was originally trapped inside the soda

Beverage companies force carbon dioxide into liquid under high pressure and low temperature. This is because gases dissolve better in liquids at higher pressures and lower temperatures. The moment you open the lid, the pressure is released, and once it enters your body, your body temperature is added to the mix. Since human body temperature is around 36.5°C (97.7°F), the carbonation in the drink rapidly loses solubility and turns back into gas.

The problem is that this re-gasification happens inside the stomach, a narrow space originally designed to digest liquids. When the trapped gas expands all at once, the stomach wall stretches. As the carbon dioxide in the stomach rapidly turns back into gas, it inflates the stomach, and the body creates a burp as a reaction to this expansion.

From here, the carbon dioxide follows three different paths.

Path 1: Burping, the fastest and most visible exit

When the stomach inflates, the body tries to relieve the pressure. The lower esophageal sphincter opens, and the gas is pushed back up toward the mouth. This is a burp. You might burp after drinking water, but that is usually because of air swallowed in the process; the burping from soda is different. It is gas that was originally dissolved in the liquid escaping explosively from the stomach.

People often have a misconception about this burp. They take the feeling of relief as a sign of good digestion. However, soda only provides a burp temporarily induced by carbonation and has nothing to do with actual digestion. Digestion is the process of enzymes breaking down food, while burping is merely releasing pressure. The relief provided by a glass of soda when you have indigestion is, in fact, a byproduct of gas dynamics that has nothing to do with stomach acid.

Path 2: Downward, without being digested, becoming flatulence

If burping is a quick escape route from the stomach, gas that misses its timing takes a different path. Some of the carbon dioxide that didn’t escape from the stomach is pushed down into the intestines. In the intestines, there is no easy way for it to travel back up. Eventually, it has no choice but to exit through the lower outlet: flatulence.

People who drink soda quickly or change their posture while drinking are more likely to have a larger share of this. This is why the pressure that wasn’t released through burping travels through the intestines and causes abdominal bloating. Drinking too much soda can lead to digestive issues like diarrhea or abdominal pain, and those with weak stomachs or sensitivity to carbonation may experience heartburn even with small amounts.

Path 3: The quiet infiltration into the bloodstream, unnoticed by anyone

There is a third, silent path that is neither a burp nor flatulence. The lining of the stomach and intestines is thin enough for gas molecules to pass through. Some of the carbon dioxide that failed to re-gasify and remained dissolved in the liquid permeates directly into the bloodstream through these membranes.

Once in the blood, the carbon dioxide joins the carbon dioxide already circulating throughout the body—the metabolic byproduct of cellular respiration. Our blood is already busy 24/7 transporting carbon dioxide produced throughout the body to the lungs. The portion absorbed from soda quietly hitches a ride on this flow and eventually exits through the lungs when we exhale. It is neither as loud as a burp nor as noticeable as flatulence. It simply mixes into each breath we take, one molecule at a time.

But there are people who don’t have the first door at all

So far, we have assumed that all three paths are open. However, there are people for whom the largest and fastest door—the ability to burp—is locked.

This is a condition called Retrograde Cricopharyngeus Dysfunction, or R-CPD. When swallowing food, the upper esophageal sphincter opens to let it pass, but to burp, this sphincter must undergo a retrograde action, opening in the opposite direction. People with R-CPD have a sphincter that does not open even when it senses pressure. No matter how much gas fills the stomach and esophagus, the exit door physically will not open.

For them, the carbon dioxide from a soda starts with the first path completely blocked. The pressure that should have been released by burping remains entirely in the body. If they cannot burp, air or gas fills the stomach, leading to symptoms like abdominal bloating, discomfort, chest pain, and frequent flatulence. It means the remaining portion is pushed entirely toward the second door—the intestines and flatulence. This is also why they experience exceptionally frequent gas.

This condition was first named in 2019 by Dr. Robert Bastian, director of the Bastian Voice Institute in the U.S., while investigating patients who could not burp. Until recently, these people were just considered to have a ‘constitution that doesn’t burp easily.’ Most lived without even realizing it was a medical condition, suffering in silence without visiting a hospital. While the condition is becoming known in Korea, with hundreds of people active in related online communities, the exact cause is still unclear.

Paradoxically, the treatment is not to force the muscle to open, but to inject Botox into it to weaken it entirely. If that doesn’t improve the symptoms, the procedure goes as far as cutting part of the muscle. You could say they are undergoing muscle paralysis just to be able to burp.

For these people, a single can of soda leads to a completely different bodily experience, even though the same chemistry is at work. It is the same carbon dioxide, the same stomach, just with one door locked—but that one door changes the entire map of the exit routes. Next time you let out a refreshing burp, it is worth remembering that for someone else, that common reflex is a non-existent option.

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Note: This article is for explaining general physiological phenomena. If you experience recurring digestive symptoms or discomfort due to an inability to burp, it is accurate to consult an otolaryngologist or a gastroenterologist.