Why does burping make noise? – Henry E., age 8, Somerville, Massachusetts
Burping is a normal part of everyday life.
Burps happen when air from your stomach travels back up your food tube – called an esophagus – to your mouth. Air gets into your stomach during activities like eating or drinking. If you drink things that contain lots of gas – like the carbon dioxide in bubbly sodas, for example – you’ll probably burp more than usual since the gas you swallowed has to come back out somehow.
Burping is important. If you don’t let the air in your stomach up and out, it heads down deeper into your digestive system. It can cause a lot of bloating and discomfort in your intestines.
That explains why people burp. But why does a burp make noise?
As the burp travels up the esophagus, it hits up against a closed, valve-like structure called a sphincter. Trapped behind that sphincter muscle, the gas builds up a lot of pressure.
It’s really hard to hold back a burp. When it finally forces its way through, the high-pressure air makes the structures in the upper esophagus and back of the throat vibrate – and that’s what causes the sound.
If you forcibly push the burp through, it increases the pressure in your esophagus, causing more intense vibrations and making the burp louder – more like a “BUURRRPP” or a “BRAAAPPP!” These are the belches that usually make your parents cringe and your friends give you high-fives.
If you gently open up your sphincter, it lowers the pressure in your esophagus and allows for less intense vibrations. These burps are more likely to be on the daintier side – more like a quieter “erp” – so probably your best bet for weddings or funerals.
The sound of the burp can take on even cooler and weirder tones depending on how you move your mouth and tongue around. This is how you can even form words or – for the truly talented – songs with burping.
So what happens if you have other gasses in the digestive system that are too far down to come up as a burp? That gas can become a fart. When you fart, gas leaves your body through another closed, valve-like structure – a different sphincter. This one happens to be called the anus.
As the gas builds up in pressure, often with a little help from your butt muscles, it causes that sphincter to finally open up. And the anus structures vibrate just like the structures in your throat during a burp. And there’s your fart.
So the next time someone says you’re burping too loudly, just reassure them that it was a perfectly normal mouth fart. That will probably go over well. You can always point out that at least it wasn’t a fart from the other end.
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George Saffouri does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.