Appliance of Science: Why do cats purr?

You don’t have to be a cat owner to be familiar with the sound of a low humming cat purr. Most people find the sound pleasant and soothing. But why do cats purr at all and how?

First the how

The cat’s purr has been quite the puzzle for scientists but they now believe that the sound is created by the vibration of muscles within the cat’s larynx (voice box). Cats purr when they inhale and exhale, unlike other sounds they make, like meowing, which they can only do as they exhale. That is why the purr often seems like long continuous sound.

Do all cats purr?

All domestic cats purr, some more than others and some of the larger wild cats do too. The cougar is the largest of the purring cats. The really big cats (lions, tigers, leopards, jaguars) do not purr; they are more known for their roar.

Kittens purr when they are just a few days old. At this stage of their lives, purring likely helps bonding between mother and offspring, as well as allowing her know where they are for feeding. Kittens can purr while they feed, providing continuous feedback to the mother.

The why

Cats keep purring as they grow into adulthood and they do so for more than just bonding and communication. They purr as a sign of contentment, as we would expect but they also purr when hungry, stressed, frightened, ill or in pain.

It is not known why cats purr in all these instances but there are a number of theories based on a number of recent studies. Scientists are unsure whether cats purr though voluntary or involuntary processes but one strongly help theory suggests that they purr in response to endorphins released when they experience pleasure or pain. When in pain, the cats may purr as a form of self-soothing but studies into the frequencies of a cat’s purr provide other theories too.

A cat’s purr is a sound of low frequency, typically 25 to 150 hertz. Low frequency sounds have been shown to affect specific parts of the body. Bones are known to strengthen in response to low frequency sounds (around 25 hertz) and skin and soft tissue cell growth can be stimulated in response to sounds of slightly higher frequencies (around 100 hertz). So are cats also purring as a form of self-healing?

Sharing the benefits

It would appear that it is not just cats that benefit from their purring. Studies have made direct correlation between regular cat contact and a reduced risk of stroke or heart disease. Cat owners that regularly pet their cats can greatly reduce their stress levels and improve their health.

All purrs are not created equal

Although to our ears a cat’s purrs may all sound the same, research has found that is not always the case. In particular, the purrs of a hungry cat contain hidden sounds that are more likely to attract the attention of their owners.

A high pitches sound is embedded in these purrs that is more like a cry and trigger an unconscious response in humans. So, while cats may be able to reduce our stress levels and possibly even help us heal, there is still little doubt as to who the real boss is in the cat-human relationship.

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