A cat contentedly being petted

Why do cats purr? It isn’t always happiness!

Introduction

Purring is the most common sound that cats make. It can be easy to hear a cat purring and to assume that they are happy. But purring doesn’t always mean that they are in a good mood.

Cats purr to communicate many different emotions. So how can you know what your feline friend is saying when they purr?

Reasons for purring

There is no single reason why cats purr. Cats purr when they are content, but I also hear cats purring when they come into the consultation room at the vets. I’ve seen some cats purring even when they are seriously unwell.

So if cats don’t just purr when they are happy, what does make a cat purr?

Happiness

The most obvious reason for a cat to purr is when they are happy. Every cat owner will have experienced the pleasant vibrating, rumbly noise when they tickle and stroke their cat.

If your cat is relaxed, eyes half-closed and tail mostly still, purring is like the sound of them smiling.

Communication

Another reason cats can purr is to communicate. Low frequency and volume sounds like purring are associated with positive social situations in mammals.

Kittens will first start to purr when they are just a few days old. It is thought that this helps their mother to locate them to feed them. Some cats will continue to purr when they are hungry for this reason.

Other cats learn to purr to communicate with their human that they want feeding. Research has discovered that cats actually have two different purrs. As well as their “regular” purr, some cats have learned a “solicitation purr”.

Solicitation purrs are higher frequency purrs that cats do purely to communicate with humans. Solicitation purrs are in the 220-520Hz frequency range. A human baby cries at 300-600Hz. For this reason, a solicitation purr is very hard for humans to ignore. Cats that know how to make solicitation purrs are subconsciously manipulating their human to nurture them.

Solicitation purring is irresistible to humans, we can’t help but look after cats when they make this noise at us!

A cat begging for food

Self-soothing

Cats enjoy purring, they not only do it when they feel good, but when they want to feel better. This is the reason why cats will purr in stressful situations or when they are hurt.

While sometimes I would like to believe that the cats I see in clinic are purring because they’re happy to see me, unfortunately it’s usually the opposite!

Healing

One of the most interesting theories about the reasons cats purr is regarding healing. It is possible that the vibrations from purring can speed up healing and improve bone density.

Cats naturally spend a lot of time lying around in wait during hunting. This prolonged inactivity could lead to bone and muscle weakness. It is thought that cats purr in order to prevent this happening and to keep their bones strong.

A cat hiding in leaves waiting to pounce

24-240Hz vibrations have been shown to have therepetic benefits to bone growth, pain relief and wound healing in humans.

In fact, there are patented devices for medical use in humans using this vibration therapy. A problem astronauts face when in zero-gravity for prolonged periods is a loss of bone density. NASA is researching the use of vibration technology to reduce this.

How do cats purr

Cats purr by vibrating their vocal cords, similarly to how human speech works. It is however a little bit different in our furry friends.

In cats, a repetitive neural oscillator in the brain stimulates the laryngeal muscles of the voicebox to twitch. The muscles twitch at 25-150Hz which causes the vocal cords to vibrate as well.

A cat with her head in a person's hand

The vibration in the vocal cords means that as the cat breathes, the vocal cords seperate and the purring noise is created. This is also the reason that cats can purr continuously, even as they breathe in.

Not all cats purr

Not all species of cats are able to purr. All domestic cats can purr, but some big cats like lions cannot. This is because cats can either purr or roar, but not both.

Cats that roar have flexible voice boxes, but purring requires a stiff voicebox. Cats that roar use this loud noise to communicate over long distances to protect their social group and territory. Cats that purr tend to be smaller and solitary, so they have less need to communicate with roars. Small cats communicate instead primarily through scent.

Purring cats and humans

Knowing that cats use their purr to manipulate humans into doing what they want can make it seem that purring is a deceptive thing.

However, purring is actually beneficial to humans that hear it. People who listen to the noise of a cat purring are 40% less likely to have a heart attack and also have lower blood pressure.

Conclusion

There is no single reason for cats to purr. They purr when they are happy, frightened, hungry and to help themselves heal.

As a vet, cats purring can sometimes be a bit of a nuisance! Sometimes it is difficult to listen to their hearts when they are purring away! I’ve found that giving them a bit of cotton wool with surgical spirit on, or running a tap will sometimes distract them long enough to have a listen. Some cats really are purr-pots though and nothing can stop them purring away!

Purring is beneficial to both cats and humans. Hearing a cat purr is not only pleasant, but actually good for your health. Here’s a prescription for your own health, you’re welcome 😉


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