Why do cats purr? Ask the average person-on-the-street and you are likely to find that most people think cats purr to signal happiness or contentment. What other conclusion could you come to when petting a cat or scratching under its chin starts its “motor” running? The cat must be happy.
Certainly, purring communicates contentment, but cats also purr under a variety of less than happy circumstances. For example, they often purr after experiencing something frightening or stressful, such as being chased by a dog. Veterinarians report that dying cats frequently purr up until the very end. These are not happy occasions, but when you think about it, not all human smiles signify joy. We smile nervous smiles and appeasing smiles, neither of which has anything to do with feelings of happiness.
So why do cats purr? There are lots of theories but no absolute certainties. Scientists do seem fairly certain about how cats purr. Almost from birth, kittens can purr. No special organ creates the purring. Rapid, coordinated muscle movement in the larynx and diaphragm combined with the cat’s breath passing over the moving muscles makes the purring sound. (Fun fact: cats that purr cannot roar, and cats that roar cannot purr.)
Knowing how cats purr drives many of the hypotheses about why they purr. A cat purrs at a low frequency of 25-100 Hz. This corresponds to the low frequency vibrations or sounds used in a variety of acoustic therapy and other healing practices. Scientists have experimented with low frequency vibrations for treating Alzheimer’s and patients with fibromyalgia, and they have conducted research on bone repair in mice. Therefore, some scientists hypothesize that the act of purring may be self-healing for cats.
The low frequency of a cat’s purr is the same as that used for “sound baths” as well as for music to help one fall asleep. This may be why petting a purring cat feels and sounds so soothing to humans. Similarly, low frequency sound has been used to reduce pain and alleviate anxiety, tension, and negative feelings. Scientists theorize that cats purr to calm themselves in stressful situations and to lull strange people or animals into believing the cat poses no threat to them, an act of submission.
Interestingly, many house cats use a different purr when hungry. The purr has an accompanying insistent whine that humans instinctively respond to as they would to an infant’s cry. The sound is unmistakably urgent compared to that of pleasant purring. As with a crying baby, attention must be paid; the bowl must be filled.
Clearly, there is a lot to learn about cats! While we may never fully understand the reasons behind purring, it should never diminish the simple pleasure derived from petting a cat. Chances are good that your feline friend enjoys it just as much as you do.