Purring cat. PHOTO: Kelly B. Jason

We like to think that a purring cat is a happy cat, but cats also purr when they are suffering. So what’s with the purring?

It’s a mystery. Scientists still don’t know how cats purr or whether it’s voluntary or involuntary. They have demonstrated that domestic cats purr both when inhaling and exhaling, and in a sound frequency range that has been known to improve bone density and promote healing. Because cats are geniuses at energy conservation, it’s possible that purring is a low-energy way to stimulate bones and muscles.

Another theory is that purring releases endorphins. So, basically, if your cat isn’t feeling well, purring has a self-healing, calming effect.

If your cat is feeling well, purring can be a way to communicate. Mother cats often purr during childbirth and nursing. Since kittens are born deaf, they respond to the vibrations and purr to communicate with Mama. Some cats purr as soon as their person walks in the room, some cats purr when you pet them, and all that purring is saying something. What it’s saying is debatable. The cat could be signaling to others that it is not a threat, that it wants to be friends, or that it wants food or affection. Or the cat could be purring to calm itself or because it feels good.

My theory: cats purr because they can.