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Spokane, Washington  Est. May 19, 1883

Ask Dr. Universe: Scientists know how cats purr, but not why

Cats purr when they’re content and when they’re stressed out, which can be confusing for their humans.  (Shutterstock)
Washington State University

Washington State University

Dr. Universe: Why do cats purr? – Kaylee, 11, Kentucky

Dear Kaylee,

Dr. Sarah Guess says purring is normal. She’s a veterinarian at Washington State University. She told me that cats purr when they’re content and when they’re stressed out. It can be a little confusing for humans.

Scientists have two ideas about why cats purr. It could have come from the way mother cats care for kittens. Or it could keep their bones and tissues healthy.

But experts don’t agree on the answer yet.

“This is a hotly debated topic among scientists,” Guess said. “Purring is something unique to cats, and when it comes to cat communication, we’re just starting to scratch the surface.”

We do know how cats purr. A cat’s brain sends a message to muscles in the cat’s throat. Those muscles begin to twitch. As the cat breathes, air whooshes over the muscle, bone and tissue in the throat. They vibrate, and that makes the rumbling sound we call a purr.

A cat’s purr can be low or high frequency. That means the sounds move through the air at different speeds. Low purrs and high purrs sound slightly different.

Some scientists think purring evolved as a way for moms and kittens to understand each other. Maybe low purrs and high purrs mean different things.

“One thought is that the different frequencies of purring relate to whether the cat is more content or more stressed,” Guess said. “That offers feedback from kitten to mother or mother to kitten.”

So, mother cats might learn how their kittens feel based on their purrs. Then, they know which kitten needs help. They might purr back to help soothe the kittens. Maybe grownup cats purr to soothe themselves. Maybe they purr to tell you that you’re making them feel safe and happy like their mother. Or to ask you to fix something that’s stressful like a slightly empty food bowl.

We know some cats knead while purring. That’s for sure a throwback to when they were kittens. Kneading on their mothers’ tummies while nursing helped the kittens get more milk.

The other idea for why cats purr is that the frequency of the purr vibration may be healing.

“Cats tend to be inactive for a lot of the day with sudden bursts of activity surrounding feedings,” Guess said. “So, maybe purring creates vibrations that help maintain bone and tissue structure while the cats are in those inactive periods.”

So, it’s possible cats purr to heal themselves and stay strong. There’s even some research that shows that vibrations at the precise frequencies that house cats purr at can help heal human bones and tissues. Maybe your cat purrs to heal its own body or to heal you.

Only a few kinds of cats purr at those frequencies – including cougars.


Dr. Universe

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