The How and Why of Cats’ Purrs

December 4, 2025

Teresa Keiger

Who can say that they do not automatically stop, smile, and relax when they hear a cat purr? A purr immediately makes us humans smile and relax—so much so that several sleep apps include a purring cat as a sound to fall to sleep by.

But…HOW do cats purr? And WHY do they possess this special skill at all? Recent studies have given us a bit more insight, but many questions still remain.

The Anatomy of a Purr

Cats have two sets of vocal folds, or vocal cords, within their larynx. The true vocal folds, which contain the thyroarytenoid (TA) muscle, are used for producing sounds like meows and growls by vibrating as air passes over them. They are responsible for all vocalizations produced by cats.  But the question remained: How exactly do cats purr?

There have been many theories over time, and most have been discarded.  Some theories posited that neuromuscular activity in the larynx creates purrs: cats contract muscles around the larynx to purr. But this isn’t how most mammals vocalize, and so that theory did not seem to make sense.  In 2023, a group of scientists tried a different approach. With the permission of the cats’ owners, they removed the larynxes of eight cats which had been terminally ill and humanely euthanized. The larynxes were immediately flash-frozen and only thawed the night before the experiment. They were then mounted on a vertical tube and heated, humidified air was pumped through the tube….and the larynxes all purred! And they purred without the use of muscular contractions.¹ This does not mean that cats do not use some sort of muscular input; just that it is not always necessary.

A second part of the purr equation is the hyoid, a U-shaped series of bones which sits at the behind the back of the tongue and runs up to the base of the skull.² In domestic cats, the U-shaped body structure is all bone. In lions, tigers, jaguars, and leopards, the hyoid bone consists of bone and cartilage. When a domestic cat’s vocal cords begin vibrating, the bony hyoid bone resonates those vibrations. It also allows the purr sound to form on both the inhale AND the exhale. Those wild cats with partially ossified hyoid bones cannot produce the purring sound as the cartilage portion will not resonate. What they can do instead of purring is roar, along with a different set of vocalizations. ²

How Low Do They Go?

Let us think about sound, from the high to the low end of the musical spectrum. Smaller instruments or other devices create higher pitched sounds, with lower pitched sounds coming from larger instruments/devices. Looking at the inside of a piano, we see that the higher notes have corresponding short, fine strings, while the bass notes have longer strings that are also wider in diameter. The same is true of the shorter-stringed violin (higher pitch) versus the longer and thicker-stringed bass (very low pitch).

A cat’s purr measures in on the low end of the tonal range, at 20-30 hertz. ¹ For an animal usually weighing 10-12 pounds/4.5 kilos, that’s VERY low. Usually animals with longer vocal cords, such as the elephant, or even large wild cats such as the lion, create these lower vocal tones.¹ How does a small domestic cat produce such a low tone?

What the researchers found was that the cats’ vocal cords were more complex than previously noted. The cords also contained fibrous masses within the vocal cords themselves. This additional material allows the cords to vibrate more slowly, producing the lower tones. In our piano string analogy, the lower base strings are not just wire. They are coiled wires so that the total mass is in a shorter length. This type of lower vocalization what is often called “vocal fry,” that raspy vibrato often heard in human speech and song.⁷ (listen to this video  for examples of vocal fry in human speech.)

But – WHY Do Cats Purr?

There is no one reason that cats purr, nor do we know all the reasons that a cat might purr. The most obvious is that cats purr when they are relaxed and happy. Indeed, many mammals use low-frequency vocalizations in positive social situations such as grooming, relaxing, and being friendly. ³ Breeders know that queens purr while nursing, and that their kittens purr while nursing. Because purring is relatively low in volume, it probably developed for short range communications. (queen to kitten, cat to another cat, etc.)

Veterinarians will note that cats also purr in stressful situations, such as during an examination. Indeed, several veterinary articles have been written about how to get a cat to stop purring while listening to its heart. Purring is also thought of as a way that cats self-calm in stressful situations. Other veterinarians have noted that cats purr when injured, and even during euthanasia, again linking the purring to a form of self-soothing. ⁴

Anecdotal evidence shows that if a cat is injured, a companion cat may lie beside it and purr. ³ Other researchers theorize that cats may purr while resting as a form of self-healing, noting that their purrs are within the same frequency range as that used for vibration therapy for healing bones in humans. However, there is no scientific evidence that a cat’s purr heals human bones (i.e. correlation does not imply causation). While researching this topic, all citations regarding research on the healing properties of purrs point to one 2006 study cited in the Journal of the Acoustical Society of America. I could find no other scientific cites.

The Take Away

What we DO know about the relationship of cats to human health is that cats – including their purrs – do help lower human stress and cortisol. ⁵ In a 20-year follow up study involving over 4000 participants (55% of whom owned/own cats or dogs) and adjusting for individuals’ other health markers, a significant number of pet owners show a decreased rate of death due to stroke and other cardiovascular disease. ⁶

So, the next time that you feel down or stressed, curl up with a cat, and relax to the purr.

Sources

1. 1. 1. Herbst, Christian T. et al. Current Biology, Volume 33, Issue 21, 4727 – 4732.e4. October 2023 https://www.cell.com/current-biology/fulltext/S0960-9822(23)01230-7
      2. Cat Chat 101: The Basics of Domestic and Wild Vocalizations. Carnegie Museum of Natural History. https://carnegiemnh.org/cat-chat-101-the-basics-of-domestic-and-wild-vocalizations/ accessed October 20, 2025.
      3. Venton, Danielle . Why Do Cats Purr? It’s Not Just Because They’re Happy. Wired
         May 8, 2015 https://www.wired.com/2015/05/why-do-cats-purr/
      4. Dowling, Stephen. The complicated truth about a cat’s purr. October 3, 2023 https://www.bbc.com/future/article/20180724-the-complicated-truth-about-a-cats-purr
      5. The Power of Pets. NIH News in Health. February 2018 https://newsinhealth.nih.gov/2018/02/power-pets
      6. Qureshi, Adbab et al. Cat ownership and the Risk of Fatal Cardiovascular Diseases. PubMed Central. Journal of Vascular and Interventional Neurology. January 2009.
         https://pmc.ncbi.nlm.nih.gov/articles/PMC3317329/
      7. Jacobs, Phie. How do cats purr? New finding challenges long-held assumptions. Science. October, 2023  https://www.science.org/content/article/how-do-cats-purr-new-finding-challenges-long-held-assumptions

    

   Teresa Keiger

   Teresa Keiger is Cat Talk’s editor and has been with the publication since 2013. She has been a professional graphic designer and photo retoucher since the mid-1990’s and currently creates many of CFA’s images. She has bred Russian Blues under the Platina Luna cattery name since the mid-1990’s and is a CFA Allbreed Judge.