Purring is one of the most familiar sounds in the house and one of the most misread. Cats purr when they are content, but they also purr when they are frightened, injured, giving birth and dying.

How the sound is made

The purr is produced by rapid rhythmic movement of the muscles of the larynx, which interrupts the airflow between the vocal folds. Because it is driven by breathing rather than by voice, a cat can purr continuously on both the in breath and the out breath, which is why it sounds uninterrupted.

The frequency is low, typically between about 25 and 150 hertz.

Purring is not only happiness

Kittens purr from a few days old, while nursing, and the mother purrs back. It begins as a signal of contact and reassurance between mother and kitten, before it is anything to do with pleasure.

Adult cats carry that meaning forward. A purring cat is often saying “everything is settled here”. But a cat that is frightened at the clinic, a cat in pain, a queen in labour and a cat close to death will all purr too. In those situations it appears to be self soothing rather than communication.

This is why we do not take a purring cat on the examination table as a sign that all is well.

The solicitation purr

Some cats develop a purr with a higher frequency cry embedded in it, close in pitch to a human infant’s cry. Owners find it much harder to ignore, and cats use it mainly around feeding time. It is a learned behaviour, aimed squarely at people.

Does purring heal

The frequencies cats purr at overlap with those used in some physical therapy to promote bone and tissue healing, and this has led to the popular claim that purring heals the cat. It is a reasonable hypothesis and it remains unproven. Treat it as an interesting observation rather than an established fact.

What is better supported is the effect on people: contact with a purring cat lowers stress and blood pressure in the person stroking it.

When purring should not reassure you

Watch the rest of the cat, not the purr. A purring cat that is also hiding, breathing quickly, sitting hunched, refusing food or not grooming is not comfortable.

Come in if a purring cat is also breathing with effort, has stopped eating, is hiding, or reacts when a particular part of the body is touched.

A cat that stops purring

A previously purring cat that goes quiet is worth noticing. It usually means something has changed: pain, illness, or stress in the household.