Why Cats Purr

To cat lovers, the feline purr is one of the most exquisite sounds on earth. Joyous and soothing, a cat’s purr can calm us in the midst of stress and relax us when we need to unwind. Animal behaviorist and author Dr. Michael W. Fox says that experiencing a cat’s purr is like getting a massage in sound.

The tiny tabby on your lap is not the only cat that purrs. Wild cats, big and small, also engage in this mysterious activity. A cat learns to purr within days after he is born. A mother cat purrs while nursing her offspring, and the kittens soon follow suit. “Very young kittens purr before their eyes are open,” says Dr. John C. Wright, certified applied animal behaviorist and author of Is Your Cat Crazy?

HOW CATS PURR
In domesticated cats, purring is produced during inhalation and exha- lation. A pause at the transition between the two is so brief as to make purring sound as if it is one continuous hum. Cats belonging to the genus Panthera (such as jaguars, leopards, lions, and tigers) purr only when breathing out because they have specialized vocal folds that enable them to roar.

How cats purr has been as big a mystery as what they are thinking, but the mechanism that causes purring is closer to being solved. “Purring involves forcing air through the glottis [the space between the vocal cords],” says Dr. Wright, “and it’s certainly related to inhalation and exhalation over the muscles of the larynx [the structure at the top of the trachea that contains the vocal cords and is commonly called the voice box].”

Past theories have suggested vibrations of the false vocal chords, blood flowing through the aorta, or even resonance in the lungs. Currently, the most accepted theory is that a buildup and release of pressure occurs as the glottis opens and closes, resulting in separation of the vocal folds, which produces the sound. The muscles of the cat’s larynx generate cycles of contraction and release every 30 to 40 milliseconds.

WHY CATS PURR
Nursing, contentment, and sexual engagement are some of the conditions under which cats may rev their motor. Although cats may purr as they rest comfortably in a warm place, it is more typical for them to purr when in contact with a person or another cat. “It’s like a handshake,” says Dr. Pamela Perry, behavior resident at Cornell University’s College of Veterinary Medicine.

Kittens purr when nursing as they knead their mother’s belly to stimulate the flow of milk. They also purr while being groomed. “Purring is a care-seeking behavior that helps establish and maintain a close relationship between a mother cat and her kittens,” says Dr. Perry.

Although cats may purr when they are rubbing against people or other cats, simple tactile contact with an inanimate object may also inspire the sound: Your cat may be inclined to purr when he’s sliding his body against the corner of a wall or when he’s rolling around on the carpet. “We really cannot know for certain what purring means,” says Dr. Perry, “but there’s some contentment associated with it.”

In addition to purring during positive activities, cats also purr under duress. Fear, anxiety, stress, injury, and recovery are other circumstances that elicit purring. The purring may be related to maintaining comfort even under extreme pain.

Whatever the cause, listening to a cat purr is one of the most relaxing activities imaginable. “Purring has a psychological and social benefit and helps to reaffirm the relationship you have with your cat,” says Dr. Wright. “Purring is something we like to hear.”

FELINE, HEAL THYSELF
No one knows for certain the purpose of purring. But Elizabeth von Muggenthaler, founder of the Fauna Communications Research Institute, a nonprofit organization in Hillsborough, North Carolina, that studies animal communications, may have solved at least part of the mystery.

Recently, von Muggenthaler determined that cats’ purring contains vibrations at several different frequencies that correspond with frequencies used in human therapeutic biomechanical stimulation to heal bones, muscles, tendons, and ligaments.

For a trait to endure thousands of years of natural selection, it must be advantageous to the species. In other words, if cats purred simply to show pleasure, purring might have gone the way of the saber-toothed tiger. “If a cat expends energy to purr during times of stress or injury, a survival mechanism has to be associated with it,” von Muggenthaler explains.

The next time you listen to your cat purr, consider that she may not just be trying to please you—she may be trying to heal herself.