Few things convey as much calm as a cat purring on your lap. But purring is not simply "I'm happy." Cats purr in very different situations, some of which are not pleasant at all. Understanding when and why they do it will help you better read your cat and realize if something is wrong.
How purring is produced
Purring originates in the larynx and sounds both when inhaling and exhaling, which is why it seems continuous. Its basic frequency is around 20-30 vibrations per second (hertz), a very deep sound for such a small animal. Some measurements place the full range, including harmonics, between about 25 and 150 Hz.
For decades, it was explained this way: the brain signals the muscles of the larynx to contract and relax very quickly, and that causes the vocal cords to vibrate. In 2023, a study on the larynxes of deceased cats managed to produce purring sounds just by passing air through, without muscular contraction. The researchers found pads of tissue on the vocal cords that could explain those deep tones. It is not settled: testing this in live cats is difficult, and it is likely that both mechanisms are involved in real life.
When they purr
1. When they are calm and comfortable
This is the most well-known case: lying in the sun, receiving pets, or kneading a blanket. Here, the purring goes with a relaxed body, half-closed eyes, and a still tail.
2. Between mother and kittens
This is likely its origin. Kittens start purring a few days after birth while nursing. Since they are born blind and deaf, the vibration is a way to communicate with the mother: "I am here and I am okay." The mother also purrs, and that helps guide them.
3. To ask for things
A study from the University of Sussex (2009) analyzed the purr that some cats use to ask for food, usually first thing in the morning. That purr has a "hidden" high-pitched component, similar in frequency to a cry. People who heard it, whether they had a cat or not, perceived it as more urgent and less pleasant than a normal purr. In other words, purring also serves to get something from us.
4. When they are in pain, afraid, or stressed
This is the most important thing to remember. Cats also purr:
- At the vet's office, even if they are scared.
- When they are injured or in pain.
- During labor.
- When they are very ill or at the end of their life.
It is believed that in these cases, purring helps them calm down or ask for care, just as a kitten asks its mother.
Do all felines purr?
Not all of them. The continuous purr, while inhaling and exhaling, is characteristic of small felines such as the domestic cat, the lynx, or the cougar, and also the cheetah. Large felines that roar, such as the lion or the tiger, do not purr in the same way, although they emit other similar low-pitched sounds when they are calm. It is believed that the difference lies in the anatomy of their larynx, although the detail is still debated.
How to know what it means
The sound is similar in all cases, so the key is in everything else. Look for these signs:
- Posture: relaxed and stretched out, or hunched and tense.
- Eyes: half-closed and calm, or wide open with dilated pupils.
- Behavior: seeking contact and eating normally, or hiding and lethargic.
- Context: the sofa after eating is not the same as the carrier on the way to the vet.
When to consult the vet
Cats are very good at hiding pain. A cat that purrs is not necessarily fine. Make an appointment if, in addition to purring, you notice:
- That they are hiding more than usual or avoiding being touched.
- Changes in appetite or drinking habits.
- Changes when using the litter box.
- Hunched posture, rapid breathing, or difficulty jumping.
Drinking little is another sign that often goes unnoticed; you have more information on what to do if your cat drinks little water.
A comfortable and quiet corner helps your cat rest and relax. In our section for cat beds and resting, you will find cave beds, bolstered beds, and hammocks.