Introduction
The soothing, rhythmic rumble of a cat’s purr is a beloved and mysterious sound. When a cat purrs, most cat owners assume the cat is content, happy, and feeling safe and secure. But researchers have found cats often purr in situations not traditionally associated with happiness, like when nursing kittens or even during stressful events like vet exams. So why do cats purr when you pet them? The reasons are more complex and scientifically intriguing than you might expect.
In this article, we’ll explore the leading theories behind feline purring, look at the science of how cats purr, and discuss the remarkable effects a cat’s purr can have. Purring seems to be much more than an expression of happiness – it may have evolved as a healing, stress-reducing, bonding mechanism cats use to help themselves and connect with others.
Purring Isn’t Just for Happiness
Contrary to popular belief, cats don’t only purr when they’re happy or content. Cats also purr when they’re sick, injured, or giving birth.1 This is because purring acts as a self-soothing mechanism for cats.2 The vibrations produced while purring release endorphins that help relieve pain and calm the cat.3 So even when a cat is stressed or unwell, they will purr to comfort themselves.
Purring Begins Young
Kittens begin purring at just a few days old, while still blind and deaf. According to Rover.com, purring helps guide newborn kittens to their mother’s teats to nurse. When it’s time for milk, kittens are guided by the vibrations of their mother’s purr. A kitten will also purr loudly to make it easier for their mother to find them if they become separated.
Purring plays an important role in strengthening the bond between kitten and mother. The soothing vibrations help calm the kitten and signal safety. Kittens that purr frequently tend to be better cared for by their mothers, according to some studies. So purring begins at a very young age as an important communication tool and expression of contentment.
Theories on the Purr Mechanism
There are two main theories that aim to explain how cats produce their characteristic purring sound. The traditional theory states that purring is created by rapid vibrations of the vocal folds within the larynx or voice box (Source). As air passes through the larynx while breathing, the vocal folds rapidly open and close, creating a repetitive fluttering sound.
However, more recent research challenges this view and proposes an alternative “diaphragmatic flutter” theory. According to this model, purring is produced by rhythmic twitching of the diaphragm, the sheet-like muscle below the lungs that helps power respiration. As the diaphragm spasms, it causes fluctuations in air pressure and vibrations that create the purr (Source). This theory helps explain why cats can purr during inhalation and exhalation.
While the exact mechanism is still debated, it’s clear that purring stems from intricate coordination between a cat’s larynx, diaphragm, and breathing muscles. The unique rumbling 25-150 Hz frequency produces a soothing, therapeutic effect for both cats and their human companions.
Purring Frequency
A cat’s purr falls within a range of 20-140 Hertz (Hz). The typical range is 25-150 Hz [1]. For comparison, the human hearing range is about 20 to 20,000 Hz. So most humans can easily hear a cat’s purr. What’s particularly interesting is that certain frequencies in a cat’s purr fall within the range considered therapeutic and healing for humans. Healing frequencies are often defined as being between 20-50 Hz, although some sources cite 40-60 Hz [2]. Since cats purr within those healing frequency ranges, it lends credence to the theory that a cat’s purr has soothing effects for humans.
The Healing Power of Purring
Studies have shown that the frequencies of cat purrs may actually promote wound healing and pain relief in humans. Research published in the Journal of the Acoustical Society of America found that cat purring frequencies fall between 25 and 150 Hz [1]. These low, rhythmic frequencies happen to fall within the range that can help stimulate bone growth and fracture healing.
Additional studies have demonstrated that sound frequencies in this range can help reduce swelling, muscle stiffness, and chronic pain [2]. The rhythmic vibrations of a cat’s purr have been associated with lowered anxiety, decreased heart rate, and relaxed muscles in humans. So when your cat curls up in your lap and purrs, it may actually be providing a healing therapy session!
Stress Relief and Bonding
A cat’s purr has been shown to provide stress relief and strengthen bonds between cats and humans. When cats purr, they release endorphins in themselves that promote feelings of pleasure and contentment (Johnson, 2021). The 25-150 Hz frequency of a cat’s purr also corresponds with frequencies that have been studied and shown to reduce blood pressure, relax muscles, and relieve anxiety in humans (Chilled Cat, 2022).
In addition, when humans pet cats, it causes the release of oxytocin (the “love hormone”) which promotes bonding, trust, and feelings of wellbeing (NBC News, 2018). This oxytocin release occurs in both the human and the cat, strengthening the bond between pet and owner. A cat’s soothing purr combined with the oxytocin release makes time spent petting cats an excellent stress-reliever for humans while also deepening the cat-human connection.
When to Be Concerned
While purring is normal for cats, changes in your cat’s purring habits or vocalizations can sometimes indicate an underlying medical issue. If your cat is purring more loudly or frequently, take them to the vet for an exam. Increased vocalizing or a change in their purr can be a sign of pain or illness (https://vethelpdirect.com/vetblog/2023/02/13/why-cant-my-cat-purr/).
Some conditions that may alter purring:
– Respiratory infections can cause congested or raspy purring (https://www.toe-beans.com/blogs/pet-blog/cat-congested-breathing-purring)
– Dental disease can be painful and change purring
– Throat conditions like laryngeal paralysis can obstruct airways during purring (https://club.omlet.co.uk/forum/topic/71208-elderly-cat-breathing-difficulties-when-purring/)
Schedule a veterinary exam if your cat’s purr sounds different than normal. Unexplained changes in purring may indicate your cat is in pain or distress.
Encouraging Purring
Creating a relaxed environment and handling your cat positively can encourage more frequent purring. Try to minimize stressors and make your cat feel secure. Speak softly, move slowly, and avoid sudden loud noises. Gently pet your cat in their preferred areas like the cheeks, chin, ears, and base of the tail. Massaging these areas releases endorphins that promote relaxation and contentment. You can also try mimicking your cat’s own purr, as the familiar vibrations may get them purring too. Be patient and keep petting sessions low-key. With time and positive reinforcement, shy or reserved cats may start to purr more readily. Remember that some cats are just naturally less vocal than others. As long as your cat seems happy and content, don’t worry if you don’t hear constant purring.
Conclusion
After all these centuries, the question remains – why do cats purr? While researchers continue to explore the origins and mechanisms of feline purring, some key points emerge:
Kittens begin purring at just a few days old, likely as a signal to their mothers. Adult cats purr not only when content, but also in stressful situations. The 25-150 Hz vibrations may promote healing and bone density.
Most importantly, purring signals a cat’s friendship and comfort with humans. Petting our purring cats lowers our blood pressure, eases anxiety, and cements the human-feline bond. Although purring remains somewhat mysterious, its calming effects benefit cats and humans alike.