Purring is music to a cat owner’s ears. But if you listen closely, you might hear your cat purring at odd times when you don’t expect it. So, do cats only purr when they’re happy, or do they purr other times too? And if they do… Why?

Do cats only purr when they’re happy? No—purring is a complex form of communication used in many different circumstances. Cats do purr to express contentment. But they also purr as a means of communication, i.e. telling a person or another cat that they aren’t a threat, or that they are present and safe. Cats also purr in what seem like ‘inappropriate’ circumstances, such as when injured or dying, either as a means of comfort or to gain assistance from human caregivers.

The guide below first looks at the origin of purring, how it made the switch from cat-to-cat communication to cat-to-person communication, and the odd contexts you might hear purring when you don’t expect to. We’ll also look at whether cats can control their purring or not!

Is Purring Always a Sign of Happiness?

Of all the kinds of feline vocal communication, purring is the one we think we know best. Purring occurs in easy-to-understand contexts: when the cat is relaxing on its own, when you pet it, or when it’s eating a kind of food it likes. It’s easy to put two and two together to understand that cats typically purr because they’re happy or content.

The Origin of Purring

To understand what purring means, we have to understand its origins. According to the Journal of Veterinary Science,

Purring has long been considered as a friendly, close-range intraspecific communication and social recognition. It has been described as a demonstration of pleasurable situation and low level of excitement. The purring appears to be calming and was considered to be an expression of seeking physical contact and would be used as an “all is well signal” by the kitten while they nurse.

In other words, purring is used by cats for several reasons. One is for the kitten to reassure its mother that it’s alive and well while it’s nursing. Cats don’t nurse their cats out in the open, but somewhere secluded and safe. It might be dark, there might be lots of smells the cat’s nose is picking up, and the mother might want to know where its kittens are without lifting its head and looking around. If the kitten purrs, none of these things are problems any more.

Purring also allows kittens and their mothers to communicate without alerting predators. The frequency and volume of a purr are so low that it can only be felt in close proximity, if not touching distance. This means that the mother can reassure its kitten of its safety, and the kitten tell the mother that it’s present and safe (and alive), without being loud enough for predators to hear.

Purring as Communication with Cats and with People

It’s only a short hop, skip and jump for this behavior to transfer to the cat-person relationship. As cats were domesticated, they needed ways of communicating with people: ways of soliciting attention, affection and food. Cats that could best get people’s attention were rewarded with treats and affection (useful for overall well-being), and so consequently lived longer and better lives. One way cats did this is by developing the meow, which cats only use to get people’s attention. It makes sense that cats would reuse an existing method of communication, the purr, and apply it in a different context.

This is backed up by scientific research. Cats purr more when their owners have been away for longer, implying that cats both purr to get a person’s attention and as a sign that they’re happy. Besides that, we also know that cats understand and respond to our emotions. You could argue that responding positively to positive emotion and negative emotion is a form of control. This is backed up by scientific studies like this one in the journal Animals.

…we found that cats correctly matched the human auditory and visual signals of “happiness” and “anger”, suggesting that they have a cognitive representation of these emotions, which allow cats to discriminate between them. This is in line with recent findings about cats’ ability to cross-modally recognize humans. Moreover, our results are consistent with previous studies demonstrating that cats are sensitive to human communicative cues and to their emotions, particularly if expressed by their owners.

This implies that cats can understand at least to an extent what their owners are feeling based on what the owner says, how they say it, and how they act. This understanding is particularly strong between a cat and the person it spends the most time with, as opposed to strangers. While cats can’t respond using the same visual and auditory emotional cues that we can, they can use their own—which is where purring comes in.

Do Cats Purr When They Are Not Happy?

But as is often the case with cats, the truth is more mysterious than you might imagine. Purring can have subtly different meanings depending on the context, and whether the cat is alone or not. Cats do purr when they aren’t happy. The Journal of Veterinary Science article linked above goes on to say:

However, contrary to what is usually believed, the purr can vary subtly and be used in several situations. Firstly, there is a variation between solicitation context and non-solicitation context purring in the human-cat interaction. It has been suggested that instead of an “all is well” signal the purr would actually be an “I am not a threat” signal as it can also be produced when cats are content and hungry but also in case of stress, pain or close to death. (Emphasis added)

This is why your cat might purr in what seem like inappropriate contexts. The first time you notice this will likely be when your cat is alone, but is purring away happily to itself. Your cat isn’t necessarily indicating that it wants affection or attention, but is signifying contentment. Beyond this, you might notice your cat purring before you feed it, which could both be a solicitation for attention and a sign that it’s hungry.

Cats can even purr in situations where they aren’t content or even comfortable. For example, cats purring during ascultation (chest examination with a stethoscope) is a well-known problem among vets. Apparently, this can be stopped by turning on a faucet that the cat can hear or spraying an alcohol-based aerosol near the cat. But this shows that cats purr in situations where they aren’t happy, comfortable or content.

Do Cats Purr When They’re Hurt?

And, yes, cats do purr when they’re hurt or even close to death too. The reasons why purring is displayed in these contexts is less clear. It could be that the cat is trying to comfort itself with the feeling of purring, since purring reminds it of times when it’s happy. Alternatively, the cat may purr so as to get your attention in the hope that you can help it with whatever’s wrong.

Can Cats Control Their Purring?

Yes—from what we know of the science behind purring, it seems that cats can and do control their purring, at least in some ways. A fascinating study in Current Biology explored this issue in depth. Here’s the abstract from their paper explaining what they found and what it means:

Despite widespread interest in inter-specific communication, few studies have examined the abilities of companion animals to communicate with humans in what has become their natural environment — the human home. Here we report how domestic cats make subtle use of one of their most characteristic vocalisations—purring—to solicit food from their human hosts, apparently exploiting sensory biases that humans have for providing care. When humans were played purrs recorded while cats were actively seeking food at equal amplitude to purrs recorded in non-solicitation contexts, even individuals with no experience of owning cats judged the ‘solicitation’ purrs to be more urgent and less pleasant. Embedded within the naturally low-pitched purr, we found a high frequency voiced component, reminiscent of a cry or meow, that was crucial in determining urgency and pleasantness ratings. Moreover, when we re-synthesised solicitation purrs to remove only the voiced component, paired presentations revealed that these purrs were perceived as being significantly less urgent. We discuss how the structure of solicitation purrs may be exploiting an inherent mammalian sensitivity to acoustic cues relevant in the context of nurturing offspring.

In short, this means that cats purr in a special way when they want something from us, like food. They change the purr so that as well as the underlying deep rumble, there’s a slight high-pitched ‘pleading’ noise that people can pick up on. Cats only use this special purr when they want something, meaning that they understand the difference between the different kinds of purr, and when to use them.

Why Do Only Cats Purr?

The answer to this question depends on how you define ‘purr’. That’s because lots of animals produce sounds that are similar to, but not quite the same as purring. A paper published in Mammal Review states that ‘[a]ccording to present knowledge ‘true’ purring is established only in the families Viverridae and Felidae of the Carnivora. Vocalizations very similar in structure occur in matching behavioural contexts in other families of the Carnivora and several other mammalian orders. Most of these vocalization types are likely to have evolved convergently.’

There are several things to take from this. One is that purring most definitely occurs in a family close to the cats, i.e. Viverridae. This is the family of civets and genets, which look a little like cats crossed with minks. These animals purr in the same way as cats. The difference between a cat’s purr and that of other animals is how the purr is made. It was only in recent years that we finally discovered how cats purr at all. It used to be thought that the noise was something to do with the inferior vena cava, a blood vessel that carries deoxygenated blood to the right side of the heart. But over time, this idea was dismissed, replaced by another: that the muscles in a cat’s larynx move, dilating and constricting the glottis, vibrating as air passes in and out. Other species in the wider group of mammals produce similar sounds, but not in the same way.