Everyone loves it when a cat purrs because a) it’s adorable and b) it means that it’s super comfortable around you, right? Like all things #science, the answer is both yes and no. Cats do purr when they’re happy, but it’s only one of many reasons that your cat might purr.
1. Because they're happy
Let’s get the obvious one out of the way first. The most frequent time you’ll catch your cat purring is as a response to social interaction, like petting or a good head scratch. According to Doctors Foster and Smith, this behavior originated as a way for a kitten to tell its mother that "all is well" while nursing. You may also catch your cat purring while they knead their paws — another holdover from their kitten days.
2. Because they're sick or injured
Yeah, it seems kind of unfair that cats will purr both when they’re happy and when they’re super sick, but that’s life. On the plus side, purring is just one of many outwardly facing signs that your cat may be sick, so you should only worry about it if they’re also acting odd in other ways.
Why do cats purr when they’re sick? Scientists think that the low rumble acts as a form of "self-soothing." Think about the things you do when you’re stressed or sick — do you obsessively organize your GIF folder, or re-watch all of Gilmore Girls for the millionth time? That’s basically human purring.
3. Because they need to regenerate bone tissue
Your cat’s purrs may have healing powers. Seriously. According to one UK study, the frequency of your cat’s purrs can help bones heal faster. Wired notes that the same science helps explain why high-impact exercise also promotes bone health — in general, pressure encourages bone growth. Scientists have also theorized that, because cats are relatively sedentary, purring can help stimulate bones so that they don’t weaken.
4. Because they're hungry
Although this sounds like a rejected plotline from a Garfield cartoon, it’s true: your cat may purr to get you to feed them. Veterinarian Benjamin L. Hart told Mother Nature Network that your cat may have learned that it can manipulate you based on the pitch of their purr. Even though a cat’s purr is a low rumble, it has elements of higher-pitched cries, which humans naturally react to.
5. Because it's a natural de-stresser for their owners
Okay, okay, this isn’t a real reason cats purr. But it is true that purring can have a positive effect on your health. It can help lower your stress levels and your blood pressure. The vibrations can also have the same healing effects on you as they do on your cat, which can be great for bone and muscle tissue. Owning a cat can also reduce your heart attack risk by 40%, which isn’t necessarily linked to purring, but it’s a fun fact you can throw at your dog-loving friends.