What does a cat's purr actually mean?
Quick answer
A purr usually means a cat is content and relaxed, but it is not a single fixed signal — cats also purr when they are anxious, in pain, or recovering from stress.
The full answer
The sound is produced by rapid, rhythmic movement of the muscles in the larynx combined with the diaphragm, which makes air vibrate as the cat breathes in and out. Because purring happens at a steady low frequency, roughly 25 to 150 Hz, it can be produced continuously and is not tied only to happy moments.
Context tells you which meaning applies. A cat purring on your lap with slow blinks and soft ears is content. A cat purring at the vet's office with a tucked tail, flattened ears, and a tense body is self-soothing. Mothers purr during nursing to reassure their kittens, and sick or injured cats often purr as a coping behavior. Some researchers also suggest that the low vibrations can support healing in bone and tissue, though that claim is still debated.
The practical rule is simple: read the whole cat, not just the sound. If your cat purrs but holds its body stiff, hides, or stops eating, treat the purr as a sign of discomfort rather than happiness and have your vet check it. Purring is not a reliable way to check for fever or illness at home. If the purr changes in rhythm, becomes raspy, or comes with breathing changes, book a veterinary visit.