Why Does My Cat Purr?
Purring is most associated with contentment, but cats also purr in stressful or painful situations — it's not a single-purpose signal.
Contentment is the most common reason
A relaxed cat purring while being petted, curled up on your lap, or greeting you is usually simply happy and comfortable. Purring often starts in kittenhood as a way to communicate with their mother while nursing, since it doesn't interrupt feeding the way a meow would.
Self-soothing and healing
Cats also purr when stressed, injured, or in pain — at the vet, during a difficult labor, or even near the end of life. The frequency range of a cat's purr overlaps with frequencies associated with promoting tissue and bone healing in some research, which has led to the theory that purring may serve a self-soothing or even physically therapeutic function, not just an emotional one.
Communication
Cats sometimes purr to solicit something from their owner — a specific "solicitation purr," often higher-pitched and layered with a cry-like sound, is associated with mealtime and tends to prompt a faster response from owners than a normal purr.
How to tell the difference
Context matters more than the purr itself. A purring cat with relaxed body language, slow blinking, and a loose tail is almost certainly content. A purring cat that's tense, hiding, or purring at the vet or after an injury is more likely self-soothing through stress or pain — worth extra gentleness and, if there's an injury involved, a vet check.