This party trick is as old as any. You take in a lung full of helium and talk in a funny voice like a cartoon character. Both children and adults find it amusing, and when decorating a room with balloons, it is almost impossible to resist. However, have you ever wondered why inhaling helium changes your voice so drastically? Some believe that the gas increases voice pitch, but that is not entirely true. It is a much more complex process where helium affects “timbre,” a rather mysterious property of sound.

Air has to travel from the lungs, through the larynx, and make changes to the vocal cords and vocal tract to produce sound.

To understand the effect of helium on your voice, you must first learn how sound works. When we speak, air goes up from our lungs and passes through the larynx. That is where it comes into contact with our vocal cords. Also known as “vocal folds,” this area has double infoldings of tissue and mucous membranes that are stretched across the larynx. When air hits the underside, the vocal cords vibrate. This vibration excites the molecules of air present in the vocal tract and creates resonant frequencies.

The vocal cord vibrations influence the pitch, and the vibration of air affects timbre, which is the perceived quality of sound that sets it apart from other sound productions. Finally, manipulating the vocal tract by moving the lips and tongue creates various resonant frequencies. That is what helps you make sounds such as “aahs” and “oohs.” In the end, when our voice leaves the mouth, it comes out in the form of waves.

So, what happens when we inhale helium?

As you have learned so far, various manipulations and vibrations have to take place to create the unique sound of your voice. However, the sound that comes out of your mouth may not be the sound that one hears. That is because where you release the sound may influence it as well. For example, a typical room is filled with approximately 0.038% carbon dioxide, 0.93% argon, 20.95% oxygen, 78.08% nitrogen, and other gases in small amounts.

Nitrogen, which is the most abundant, is seven times denser than helium. Sound waves travel through helium much faster because it is lighter than air. If the temperature of a room is 68 °F, the sound will travel through the air at 344 meters per second. However, if the room is filled with helium, the same sound will travel at 927 meters per second. Therefore, by inhaling helium, you are actually changing the air molecules present in your vocal tract. So, the sound of your voice travels much faster than normal.

As mentioned above, helium does not change the pitch, but it affects the timbre of your voice. When sound travels fast through helium molecules, it also changes the resonance of the vocal tract which becomes less responsive to low-frequency sounds and more responsive to high-frequency ones. As a result, your voice comes out flat, making you sound like Donald Duck.

Though it might be hilarious, you must not inhale too much helium as it can have an adverse effect on your health.

Even though you may have fun with helium, you should be careful. Inhaling helium disrupts respiration. Since you are not breathing normally, your lungs do not get enough oxygen which can lead to asphyxiation within minutes. When inhaling helium, if you start to get dizzy, you should stop immediately. Also, do not ever inhale helium from pressurized tanks. These have a high flow rate that can rupture your lungs. Inhaling a large mass of air at once can also result in seizure, stroke, and even death!

(Sources: 1, 2, 3, 4 )