Why do cats purr?

If you have ever been fortunate enough to sit with a purring cat in your lap, you will know how soothing and calming a feeling it is. Studies have shown it can even lower your blood pressure and relieve stress. But what is the reason for this very feline behaviour and what are the cats themselves getting out of it?

The act of purring emanates from the cat’s voice box, or larynx. When cats breathe, they dilate and constrict the glottis, the area around their vocal cords, in a rapid, rhythmic fashion. As the air vibrates over the laryngeal muscles of their larynx, the purring sound occurs.

The "roaring cats" (lions, tigers, jaguars and leopards) have an incompletely ossified hyoid bone of the larynx, which enables them to roar but not to purr. All remaining species of the family felidae ("purring cats") have a completely ossified hyoid, which enables them to purr but not to roar.

So what are the reasons for purring, or at least our human understanding of them?

Kittens are born blind and deaf and remain that way for roughly the first two weeks of life. They begin to purr, however, after two or three days, mostly when the mother cat is feeding them. It’s thought to promote the mother-kitten bond and encourage further feeding.

Purring before and during eating continues into adulthood. Cats will often add in a high-pitched chirrup when waiting to be fed which is of a similar frequency to a baby crying and is designed to get our attention and instigate feeding more urgently than a purr alone. Listen for this next time you feed your cat and think about the feelings it creates in you.

Cats often purr when they are stroked, which is thought to be a sign of happiness or to show you that they like the attention and that it should be continued. This purr will often continue when they are grooming or drifting off to sleep, and so can be seen as a form of self-soothing, like a child sucking their thumb.

Big cats in the wild have been shown to purr with various injuries, such as leg fractures, or during labour. This purr is thought to promote tissue healing and give pain relief while reducing cortisol levels, which would otherwise delay healing. This may be why domestic cats tend to have fewer complications after surgery than other domestic species such as dogs.

Cats can adapt their vocalisation to the environment in which they live. For instance, a cat that lives with a deaf owner will reduce the amount of meowing that they perform but increase purring as their owner can feel and react to the vibrations.

Purring is certainly a form of communication, not only with other animals, but also with themselves. A purr is a warm smile, a big hug and a sigh of contentment. It’s a sign of inner peace and a call for attention. It is soothing and stimulating and can sometimes be healing.

So let that cat sit on your lap for a little longer and listen to their inner thoughts. You may be better off for it.

• Lucy Richardson graduated from Edinburgh University in 2005. She started CedarTree Vets in August 2012 with her husband, Mark. They live at the practice with their two children, Ray and Stella, and their dog, two cats and two guinea pigs. She is also the FEI national head veterinarian for Bermuda