Why do cats purr? There can be little doubt that a purring cat is one of the most relaxing noises known to man. Like white noise, a cat’s purr is naturally soothing and can make anybody smile. But why does the feline breed make this noise?
People who spend a lot of time with their cats will notice there are a couple of different types of cat purrs and these differ from why cats meow. This is because cat purrs can have different meanings! A purr when playing with a great cat toy is different from the purr they make when lying on your lap, or even the purr from inside their cat box on the way to the vet! But although scientists have worked out how cats do it, they still aren’t sure why cats purr. There are lots of possibilities – let’s take a look at them below.
After graduating as a veterinarian from the University of Nottingham, Dr Joanna Woodnutt went on to practice companion animal medicine in the Midlands, UK. Dr Woodnutt is specifically interested in consulting and helping her clients understand their pets better, whether it’s around medical problems such as dermatology, behavior, and nutrition.
What does it mean when cats purr?
Cats can purr for several reasons, and scientists still have lots of unanswered questions about cat purrs. Cats can purr when they’re happy, but also when they’re afraid or in pain, and as part of some social situations. Knowing that there are several different cat purrs has complicated research into them, as it’s hard to tell what a cat is thinking at any given moment. And until recently, people have been more interested in dog communication (such as people wanting to find out how to stop a dog from barking in their crate) moreso than cat noises – but that’s starting to change. Here are some of the reasons we’ve identified as possible meanings for cat purrs.
The most well-known reason for cats to purr is when they are contented. Cats will purr when sitting on a warm lap or in their own bed, especially if they have a full belly and have had a satisfying day. However, while we do assume this purr is purely an expression of contentment, there may be underlying reasons why cats purr when relaxing, like healing (see below), which complicate matters. Despite it being a long-held belief that cats purr when happy and relaxed, it may be that one of these other reasons is actually causing the cat purr and we’ve been misinterpreting it the whole time!
Stress and pain
All vets, myself included, can tell you that some cats seem to purr no matter what. We’ll have cats in with broken limbs, and they’ll still be purring. Others will purr all the way to us in their cat boxes, despite clearly being terrified. So, cats don’t always purr from happiness and contentment, sometimes stress and pain can cause cats to purr. We don’t know if this is a self-soothing behavior, or whether one of the following reasons cats purr could be at play.
Scientific studies, including one published in The Journal of the Acoustical Society of America, have found that cat purrs sound at 25Hz to 150Hz. Hz which stands for ‘hertz’ is the measurement of frequency of a noise. Higher frequencies make a higher pitch, with the human ear able to hear sounds from 20Hz to 16,000Hz. Within this range, cat purrs often sit at 25Hz and 50Hz- which according to the Chinese Journal of Surgery are frequencies known to help with bone repair and healing. They also have a harmonic (or overtone – a second, higher, frequency that can sound at the same time like a chord) at 100Hz, which is therapeutically used for pain relief and wound healing. So, while it’s possible your cat is purring from contentment, they may also be purring as pain relief and as a form of self-medication to keep bones strong. Healing and pain relief may explain why cats purr when they’re in painful or stressful situations.
It also seems clear that cats use purring as a form of communication. Certainly, cats purr in social interactions, such as when allorubbing (rubbing against other friendly cats to share scents) or when greeting their owners after spending time apart. In fact, one study published in the PLOS ONE journal showed cats purred more the longer they had been separated from their owners. This suggests they see us as part of their family, how cute!
Asking for food
We also know that kittens start purring at just a couple of days of age and can use their purrs to request food from their mother. Some cats seem to carry this purr on into adulthood and use it to request food from their human family too. In fact, one study conducted by the University of Sussex showed that cats have different types of purr – and even non-owners can hear when a cat’s purr becomes needy as if they’re asking for something! This ‘solicitation’ purr has a high-frequency whine behind it and appears to activate the parts of our brain hard-wired for nurturing our offspring.
Do all cats purr?
While all cats can purr, the amount that a cat purrs is individual. Some cats purr a lot, and others less. Some might purr only in certain situations, while others will pretty much constantly purr. As long as the amount of purring remains fairly constant, it’s probably normal for your cat to purr less or more than other cats. However, sudden changes in purr should be investigated in case your cat is masking pain or stress.
It's probably worth mentioning here that other species of cat purr too! While domestic cats are the most well-known for purring, studies have shown that servals, ocelots, cheetahs, and pumas also purr, and the frequencies are similar to cat purring.
Are cats trying to communicate with you when they purr?
Whether or not your cats are purring to communicate depends on the situation. As we saw above, some cats are adept at pitching their purrs to ask for food or attention from their owners – in which case, they’re definitely trying to communicate. Even purring as part of a social bonding ritual – alongside rubbing against you to exchange scents – is communication. We don’t know if purring in stressful situations is designed to get us to help them or whether it’s pure instinct, but it’s possible this sort of cat purr is also designed to tell you exactly how they’re feeling.
However, some purrs are probably only meant for cat ears. Lots of cats purr when alone, and we don’t know why. It may be that they’re just purring because they’re happy and relaxed – the same way we might sigh when curled up on the sofa with a good book. But it’s also possible that these purrs are a way of healing minor injuries, or strengthening their bones and muscles despite being stationary. Either way, not all purrs are a form of communication!
So, it turns out that “why do cats purr?” isn’t an easy question to answer after all, and scientists still aren’t sure of the purposes of cat purrs. It’s likely that there are a lot of different types of cat purrs, with lots of different meanings and uses. The important thing for us pet parents is that we don’t assume our cat is happy when they are purring – there could be another reason your cat is purring, so keep your mind open and try to listen to your cat!
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Dr Joanna Woodnutt is an experienced vet with a passion for companion animal medicine and helping pet owners with a variety of issues like dermatology, nutrition and behavior. Jo started writing about pet health in 2017, realizing that it meant she could help even more pet parents. Since then, she has written for countless online and print publications and is a regular contributor for Edition Dog Magazine.