How and why do cats purr?
The short answer
Cats are able to purr through vibrations of the muscles around their vocal cords, triggered by specific brainwaves. Cats seem to purr because they are content, want to self-soothe in times of distress, are repairing bones and muscles, and are communicating with other cats.
The long answer
How do cats purr?
A cat's purr starts in its brain. There is a unique, rhythmic, repetitive neural oscillator (brainwave) in the cat's central nervous system that sends a signal to its laryngeal muscles to vibrate.
The laryngeal muscles are responsible for opening and closing the space between the vocal cords. When these muscles vibrate at a rate of 25 to 150 vibrations per second (or Hz, for my fellow music nerds), a purring sound is produced. The reason why we know this is the cause of purring is because cats with laryngeal paralysis can't purr. Interestingly, cats can purr simultaneously while breathing in, breathing out, and meowing.
What's still up for debate is if a cat can purr on command or whether it is an automatic response (or both). Unfortunately we can't ask cats about this.
Why do cats purr?
The bottom line is we don't know for sure why cats purr, but researchers have made inferences based on cats' behavior.
Kittens, born blind and deaf, begin purring a few days after birth as a way to find and communicate with their mom. Both the mom and kitten purr while they are nursing, which likely contributes to bonding.
As a kitten grows into a cat, it continues purring in different situations. Here are four reasons why cats seem to purr:
Reason #1: They are happy or content.
As many people with cats will attest, a happy cat is a purring cat. This is the most common reason a cat will purr and makes sense given the immediate positive association it made as a kitten of purring in the safety and warmth of mom. As a bond grows between a person and their cat, even mere eye contact can trigger a cat's purr to go off.
Reason #2: They are scared.
Just as humans engage in nervous laughter, cats seem to purr when they're scared or anxious, like when they're at the veterinarian's office. Purring is likely a form of self-soothing as a way to cope during moments of distress.
Reason #3: They are sick, in pain, or injured.
In addition to purring likely being a form of self-soothing, it's also arguably a form of self-healing. The frequency of purring vibrations has evidence of being a natural healing frequency that can strengthen and repair bones, relieve pain, and heal wounds. NASA has even researched simulating cat purring as a way to prevent bone density loss in its astronauts. Purring, it seems, is a low-energy way to maintain healthy bones and tissue while resting.
Reason #4: They are communicating with other cats.
Finally, cats also seem to purr when they interact with other cats as a form of communication. Kittens use a combination of purring and meowing to tell their moms that they want to be fed. Cats routinely employ this tactic as they grow into adulthood, meow-purring at their human counterparts to open that can of food. Additionally, older cats seem to purr to younger, stronger cats as a way of letting them know that they are not a threat.
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Sources
BrainStuff - HowStuffWorks. (2014). How (And Why) Do Cats Purr?YouTube. Retrieved August 24, 2023, from https://www.youtube.com/watch?v=7_zKkBKu1fs&ab_channel=BrainStuff-HowStuffWorks
Dowling, S. (2018, July 25). The complicated truth about a cat’s purr. BBC Future. https://www.bbc.com/future/article/20180724-the-complicated-truth-about-a-cats-purr?mod=article_inline
Duff, M. (2023, May 6). Why do cats purr?. LiveScience. https://www.livescience.com/animals/cats/why-do-cats-purr
NASA. (2001, November 2). Good Vibrations. NASA. https://science.nasa.gov/science-news/science-at-nasa/2001/ast02nov_1
Stuart, A. (2012, April 21). Why Cats Purr. WebMD. https://www.webmd.com/pets/cats/features/why-cats-purr
Why and how do cats purr?. The Library of Congress. (2019, November 19). https://www.loc.gov/everyday-mysteries/zoology/item/why-and-how-do-cats-purr
