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cats purr when they are happy. it is a form of communication to express that they are content or to say "i love you." it also is thought to perhaps have a healing effect when they are sick or injured. it occurs in the throat area by a certain way of their breathing. i think i read somewhere that there is a flap through an airway so that when they breath that way they purr.

Although we assume that a cat’s purr is an expression of pleasure or is a means of communication with its young, perhaps the reasons for purring can be deciphered from the more stressful moments in a cat’s life. Cats often purr while under distress, such as during a visit to the veterinarian or when recovering from injury. Thus, not all purring cats appear to be content or pleased with their current circumstances. This riddle has lead researchers to investigate how cats purr, which is also still under debate.

Scientists have demonstrated that cats produce the purr through intermittent signaling of the laryngeal and diaphragmatic muscles.

Cats purr during both inhalation and exhalation with a consistent pattern and frequency between 25 and 150 Hertz. Various investigators have shown that sound frequencies in this range can improve bone density and promote healing. A newer theory is that purring releases endorphins - natural analgesics that reduce pain while healing proceeds.

One study determined that purring involves activation of nerves within the voice box. These nerve signals cause vibration of the vocal cords while the diaphragm serves as a piston pump, pushing air in and out of the vibrating cords, thus creating a musical hum. Veterinarian Neils C. Pederson, author of Feline Husbandry, believes that purring is initiated from within the central nervous system and is a voluntary act. In other words, cats purr only when they want to. The other theory is that the sound comes more from vibrating blood vessels than in the voicebox itself.

"No one knows, really, how cats purr. Although you are correct, it is believed to be the vibration of blood vessels rather than something vibrating in the cat's larynx. Cats are all allegedly supposed to have the ability to purr, but I am not sure there is evidence that "big" cats have been observed "purring" (but see leopard, below). Cats also purr not only when they are allegedly content, but perhaps during any time of sensory stimulation or stress (for instance, cats purr while giving birth, something I certainly wouldn't have done the two times I gave birth!). The purring mechanism has been attributed qualities of communication (see below), "oscillatory regulation" (cats can continue to purr even when the nerves to the area are experimentally severed) and sensory interaction with the environment. According to the Britannica Encyclopedia:

'While lions and other big cats roar, domestic cats and other Felis species purr. Purring has been described as a low, continuous, rattling hum and often is interpreted as an expression of pleasure or contentment. Purring also occurs in cats that are injured and in pain, however, so that this vocalization can be seen as the cat's 'mantra'--that is, as a relaxing, self-comforting sound and a friendly mood-conveying signal...

The calls of the leopard vary and include a series of harsh coughs, throaty growls, and deep, purring sounds...'

There are also about a zillion cat links on the internet, where there are daily chat groups with verterinarians and lay persons, wherein the lastest "purr science breakthroughs" may be discussed. Try this link:

FYIpurr

This link will ultimately try to sell you stuff, but part of their text reads:

'How does a Cat purr?'

No one really knows. Purring is a mystery. No one can definitively say which mechanisms in a cat create a Purr. The Purr, so familiar to Cat lovers' ears, is created, according to some feline experts, by the vibration of a Cat's vocal cords when it inhales and exhales. Yet, others who have studied felines believe Purring is a vibration caused by blood passing through a large vein in a Cat's chest.

Beyond the mystery, what attracts humans to a Purring Cat?

Initially born blind and deaf, what unites the newborn kitten with the Mother Cat is...the Inner Purr. During nursing, both kitten and Mother Purr in a symphony of physical and psychological Contentment. The Inner Purr connects a Cat to its Mother...to its owner...to the world around it...and to its own purr-fect Contentment....

They then proceed to try to sell you tapes of purring or something for self-enrichment (hey! You can get anything you want on the internet!), but from this site, you can link to several other cat sites.

'Purring' has also been attributed to other mammals, such as civets and other mustelids, but I don't think 'purr' has a legitimate scientific designation.

Right now, in other words, we don't know, but these are our best guesses!"

Cats often purr when being petted, becoming relaxed, or when eating. Female cats are known to sometimes purr while giving birth. Domestic cats have been reported to purr when injured, sick, in pain or dying. Purring may be a signaling mechanism between mother cats and nursing kittens. One theory is that it is not a sign of showing love but attempting friendship, for example, when a cat is nervous (at a Vet perhaps) it may purr to avoid being hurt. German ethologist and cat behaviorist Paul Leyhausen interprets it as a signal that the purring cat is communicating that it is not posing a threat.

I'm curious too. My cat always purrs. She's not even a kitten anymore and every time I look at her or say her name, she starts purring like crazy! People come over and ask why the cat purrs so much....

Sorry I didn't answer, but I want to know the answer too.

I don't know for WHY they purr. I do know they don't just because they are comfy. They purr when they're scared, when they're giving birth, when they're dying, I don't know why! I'm sorry. I love my Raider. Great cat. 1 Of many I've had all my life. Cats purr!

they purr to show that there happy. but thats not always the case some times it cuz the see somthing small like a mouse or rat am they egt into a hunting mode but thats cuz young cats like to hunt and they get excited.

Either they are in pain or that is their way of protecting you. Or there blood is just flowing and that is what makes the purr sound anyway.

To Show They Love You.