Stroke a cat in the sun and you’ll often feel it before you hear it: a low rumble running through its whole body. We take it to mean the cat is happy, and very often it is.
But cats also purr at the vet, when they’re injured, and while giving birth. The purr is less a smile than a signal, and what it says depends on when the cat uses it.
In short
| How it’s made | In the voice box, as the cat breathes in and out. |
|---|---|
| When | Content, but also hurt, stressed, giving birth, or hungry. |
| The feed-me purr | Has a high cry hidden inside it that people find hard to ignore. |
| Does it heal bones? | An interesting idea. Not proven. |
How a purr is made
A purr comes from the larynx, the voice box in the throat. Unlike a meow, it keeps going as the cat breathes in and as it breathes out, so it sounds like one unbroken rumble. It’s very low: around 25 beats a second, lower than the deepest human bass voice.
For about 50 years, the accepted explanation was that the brain fires the throat muscles on and off, around 25 times a second, to make the sound. Then in 2023, a team led by Christian Herbst at the University of Vienna found that a cat’s voice box can purr with no help from the brain or muscles at all, just with air blown through it. Inside the vocal folds they found small pads of tissue, up to 4 millimetres across, which seem to let a small animal make such a low sound. The researchers say this doesn’t fully rule out the old explanation. The muscles may still help.
Mothers and kittens
Purring starts early. International Cat Care notes that kittens purr while they feed, and mothers purr back to reassure them. A newborn kitten can’t see or hear, but it can feel its mother’s purr through its body.
That may be where the purr’s real meaning lies: it’s something cats say when they’re close to someone. Grown cats purr when they greet each other, when they groom each other, and on a lap.
Purring when it hurts
This is the part that surprises people. Cats often purr under stress, at the vet, or while recovering from an injury, writes Leslie Lyons, a cat geneticist then at the University of California, Davis. Many also purr in the early stages of giving birth.
Nobody is sure why. It may soothe the cat itself, a bit like a person humming when they’re nervous. It may be a signal to others: I’m no threat, please look after me. Either way, a purring cat is not always a fine cat. A cat that purrs but hides, won’t eat, or doesn’t want to move needs looking at. Our list of signs a cat is sick can help.
The feed-me purr
Karen McComb, who studies animal communication at the University of Sussex, had a cat called Pepo who woke her every morning with a loud, insistent purr. So she studied it. In 2009, her team recorded ten cats purring at two kinds of moment: while they were asking for food, and while they were just resting.
They played the recordings to 50 people, at the same volume. Listeners rated the feed-me purrs as more urgent and less pleasant, even people who had never owned a cat. The difference was a high-pitched sound mixed into the low purr, a bit like a cry. When the researchers took that cry out of the recording, the purr sounded much less urgent.
McComb thinks cats may be tapping into the way people respond to a crying baby. It’s more polite than a yowl at 5 a.m., and harder to ignore. The team found it mostly in cats that live closely with one person, rather than in busy households, so it seems to be something each cat learns.
Can a purr heal bones?
You’ll read online that a cat’s purr heals broken bones. The idea goes like this: purrs sit at low frequencies, roughly 25 to 150 beats a second, and vibrations in that range have been linked to bone strength and healing in other studies. In 2001, the researcher Elizabeth von Muggenthaler presented the idea that cats might purr to help keep their own bones and muscles strong.
It’s a lovely thought, and it may be true. But it is a hypothesis. No study has shown that purring heals a cat’s bones, or yours. A hurt cat needs a vet, not just a purr.
Which big cats purr?
Cheetahs and pumas purr, just like house cats. Lions, tigers, leopards and jaguars roar instead. The usual rule is that no cat can both purr and roar. The difference is often put down to the small bones in the throat that hold up the voice box: stiff in purring cats, partly flexible in roaring ones. Some researchers think the story is more complicated than that.
The snow leopard is the odd one out. It belongs to the same family group as the lion, but it can’t roar, and it makes purr-like sounds instead.
Questions people ask
Does purring always mean a cat is happy?
No. Cats purr when they’re content, but also when they’re stressed, in pain, giving birth, or asking for food. Look at the whole cat: its body, its eyes and where it is.
How do cats purr?
The sound comes from the voice box as the cat breathes in and out. A 2023 study found small pads of tissue in cats’ vocal folds that let them make such a low sound.
Can a cat’s purr heal bones?
It’s an idea, not a proven fact. Purrs fall in a frequency range that has been linked to bone healing in other research, but no study has shown that purring heals bones.
Next time a street cat purrs at you, snap it and give it a name. It’s telling you something.
