How and Why Cats Purr

In addition to the messages purring can send to you and others, it offers physical benefits to both felines and the lucky people petting them.

Purring Mechanics
Despite all of our high-tech advancements, the anatomical and mechanical roots of your cat's purr aren't entirely known. "Theories are that it is a vibration of the larynx [voice box] or diaphragm," says Elaine Wexler-Mitchell, DVM, author of Ask the Vet about Cats (BowTie Press 2004). "The vibration is stimulated by neural messages sent from the brain."

Cat behavior expert Amy Shojai, author of PETiquette: Solving Problems in Your Multi-Cat Household (M. Evans 2005), says that purring results when laryngeal muscles alternately open and close the glottis [the combination of the vocal chords and the space between the folds], causing a sudden separation of the vocal chords. The sound is due to the sudden buildup and release of pressure from the inhaling and exhaling of breath.

Purring Messages
Even though your cat purrs the same way no matter what's going on, the circumstances surrounding the purring determine what your pet is communicating. Often it's contentment - a reflection of your cat's perception that all is right in its world. However, those feline rumbles may be sending a different message in some situations. These messages include:

"I'm a Nice Kitty"
Some cats may purr to signal to other cats that they're friendly and want to come closer to them. In certain situations, a cat purrs to signal to another party - feline or human - that it poses no threat to that individual. If your cat purrs while being handled at the vet and also head bumps with forward-facing ears, she's probably signaling that she poses no threat and feels minimal fear.

"I Want To Reassure Myself"
A cat that's feeling nervous or upset may respond by purring. "Cats that are gravely ill will purr," notes Wexler-Mitchell. "Purring in this situation may provide some comfort." Dying cats are also known to purr, as are cats giving birth.

"I'm OK, You're OK"
Many experts believe that kittens, which can purr when they are only 2 days old, do so to signal to their mothers that everything is fine. The mother not only hears the sound of the kitten's purring but also feels the vibration. Mother cats are likely to purr back to their offspring in the same spirit of reassurance.