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I've read it on Wikipedia's article about purring (in French), which I will paraphrase as follows:

Veterinarians think that cats heal fractures etc. more rapidly than dogs. [citation]
A hypothesis alleges that purring may have a healing effect on bones etc. [no citation]
Many cats emit purring whose frequency permits calming of pain. [citation to a psychology article] Purring might therefore be a way to maintain the health of the cat.

Here is another quote about it :

The type of frequencies that are found in the cat's purr are good for healing muscle, tendon, and ligament injuries, as well as for muscle strengthening and toning. They are good for any type of joint injury, wound healing, reduction of infection and swelling, pain relief, and relief of chronic pulmonary disease.

Source

If true, could you please tell me about how much effect it has ?

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4 Answers 4

up vote 17 down vote accepted

Interesting claim! My delving suggests that this might be a fine line between truth and woo. First, the woo. I have strong suspicious about the following quotes from your provided SOURCE.

Since cats purr when they are severely injured or dying, it has to be survival-related.

Not really. See some reasons cats might purr HERE. Note that I said might. It doesn't seem that we really know. Self-healing is speculated, but I followed Wiki's link for that suggestion over HERE to Scientific American and was sorely disappointed. No sources, no specifics cited... it reads like an editorial opinion piece based simply on intuition and speculation.

The type of frequencies that are found in the cat's purr are good for healing muscle, tendon, and ligament injuries, as well as for muscle strengthening and toning. They are good for any type of joint injury, wound healing, reduction of infection and swelling, pain relief, and relief of chronic pulmonary disease.

Wow. Huge claim and one would think that we'd have heard about it by now if it had such wide effects. My honest thought when reading this is that the same could be said of certain shades of purple quartz -- but only certain shades. Again, no sources whatsoever about how such effects were determined as "good" for such illnesses.

Some stats for cat vs. dog lameness and other sicknesses are given (cats come out ahead -- surprise), followed up by this:

This basically says that cats are in fact healthier than dogs are. People like to say, "Oh, that's just coincidence," but it can't be. The odds of its being coincidence are like three billion to one.

No idea where the statistics are coming from. By this reasoning, if we take any species and compare illness rates to another species, should we conclude that all instances in which one does better than another simply cannot be a coincidence? Re. the claim that cat bones heal faster; I could find no such evidence in my searching. Every search phrase returns that site or a copy-cat of it, though.

Animals have so much more than we have. As humans we are limited by what we're able to see, hear, and smell. Our senses are nowhere near as keen as those of a dog or a cat. You may have seen your own cat at times looking at something you cannot even sense, much less see. Most humans presume that their cats are just staring into space, but they are tracking something.

Again, we have no idea. A cat literally might be spacing out. We anthropomorphize and pattern-seek out a "contemplative look" on their faces and thus assume they must actually be contemplating. Until we rig up some better inter-species communication or analysis techniques for lower animals, we just won't know what a cat/dog is "thinking."

Now, onto the potential truth. First of all, I think this area has been clouded with woo. Note the results for the google phrase, "using sound waves for healing". Lots of hinting at "deeper levels," spiritual refreshment, the bringing about of "oneness" and the like. See THIS for an example of what I'm talking about.

I did find some references that indicate that audio frequencies may be beneficial for bone growth.

  • HERE is the abstract for a study in which a 1Hz frequency on the tibias of rabbits provided measured improvement in bone strength.
  • HERE is Wiki's summary of beneficial results from low frequency ultrasound stimulation of bone and teeth.
  • HERE is a 1990 granted patent for bone growth therapy via "acoustic shock waves." Skip down to the bottom of the second to last page and last page for what are called the "claims." These are the directly stated novel inventions being claimed. Note that the treatment requires shock waves powerful enough to cause the bone to bleed in order to stimulate growth.
  • HERE is a summary of an experiment to examine ultrasound on animal bones, but no results are provided.

So... what to make of this? It seems that low intensity ultrasound has definite evidence going for it in terms of bone growth stimulation. Also, acoustic shockwaves from the patent are also cited, but my skim showed them referring to frequencies in the ultrasonic range as well (I could have missed something, though). However, a cat purr is not going to use their supplied method of causing bone bleeding.

I could find no evidence for the claims that I think would be required to support what you're asking about, thought. Namely, nothing supporting:

  • cat purrs themselves for healing bones, various illnesses and/or other bodily damage
  • acoustic waves themselves in the range of 50-150 Hz (the range of purring frequencies) for healing

For one last thought... we are quite ignorant of all the variables involved the body's healing. One's outlook, the placebo effect, stress levels, etc. I wouldn't doubt that one's psychological disposition due to the presence of a beloved pet really could have an effect -- I just don't think there's anything particularly amazing about the "power of a purr" at this particular moment :)

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Nice answer, thanks. :) –  POSIX_ME_HARDER Jun 5 '11 at 11:21

TL;DR: This is a speculative conjecture. The proponent hasn't yet published any experiments to demonstrate the effect.

The cite in the question is to an article called The Cat's Purr for Healing which excepts from a book by Paula Peterson, who interviewed a researcher called Elizabeth Von Muggenthaler, so that is where we must go to find the evidence.

Von Muggenthaler is the President of Fauna Communications Research Institute. You can visit the site and get a feel for how august this institution is. They offer Reiki to help with your pet's behaviour problems, and have a Spiritual adviser on staff because:

Without Spirit, (God) you have no science.

But this doesn't mean what they claim is wrong, just that you should have your skepticism hat firmly fastened before continuing.


The core idea is outlined in on their web-site:

The web-site claims it has been peer-reviewed, but conference proceedings often go through minimal review, I haven't been able to check the level of review at that conference.

The argument in the paper is basically as follows:

  • Felids (cats) purr even when they are not contented, but injured.
  • There must be some evolutionary advantage. (A fallacy!)
  • Cats recover faster from operations, and have certain types of complications less often than dogs, who don't purr. (A poor control!)
  • Some other scientists claim that low frequency motion (20-50 Hz) can help in the development and healing of bone. An example is given of chickens stuck standing on a moving plate getting stronger bones. In another study rabbits with radius fractures were mechanically vibrated and healed faster. (This study tried no vibrations, 12.5Hz, 25Hz, 50Hz, 100Hz and 200Hz. They all apparently worked - the study is in Chinese, so I can't easily check - but 25 and 50Hz were the best.)
  • They decide that the (invented term) "anabolic frequency" is 25Hz-50Hz, or 20-140Hz or 120Hz. (It helps to have a few different targets that can be declared hits.)
  • They measure the purrs of several species of cat, and discover the "dominant and fundamental" frequency is exactly 25Hz... or 50Hz, which they describe as the "best frequencies for bone growth and fracture healing" (which is nonsense; they were only shown to be the best of five tested. No-one knows if 31.34Hz wouldn't be better still.)
  • They find similar coincidences for harmonics and tendon recovery, with the harmonics falling exactly on 120 Hz (except for the ones that didn't), and so on.

They conjectured that cats must purr to help their own healing process.

Unfortunately there is no easy way to test this hypothesis. Purring-cat physiology would have to be compared to non-purring cat physiology to test this theory. The study would have to be entirely non-invasive.

No. No, it wouldn't. If this had any real chance of being true, the potential impact on human health would be great - I am sure Ethics Committees would approve invasive steps to depurr some cats, if such a process was possible.

They claim that "the scientific version of this paper has been submitted for review". I would have expected this process to have finished after 6 years (or 11 years after it was first presented at the 2001, 142nd annual Acoustical Society of America, American Institute of Physics, International Conference).

They are also appealing for help and money to further the research.

So where did we get? We have some studies that show vibrations may help some healing, we have a study that show cats purr, we have a ten-year-old wild conjecture that cats purr to help healing, and we have some appeals for money.

I think in conclusion, we can say that this claim has not been proven.

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There are many things that work in medicine/healthcare without people knowing exactly why. Trial and error is par for the course, particularly with psychology. As of yet there are no hospitals with beds that vibrate or play sounds similar to a cat's purr.

Desmond Morris has opinion on why cats purr when they are in a bad way, e.g. on the table at the vet's. He believes the purr is to induce a calm 'don't hurt me' mood. His book is a good read for any cat lover:

http://www.amazon.co.uk/Catwatching-Essential-Guide-Behaviour-ebook/dp/B0031RS5C4

I just hope you don't have to find your cat injured from a road accident and purring, it is very sad.

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You haven't explained why we should care about the opinion of some guy called Des. Does he have any actual empirical evidence to support his claims? –  Oddthinking Jul 13 '12 at 6:45

According to Wikipedia "Scientists at the University of California, Davis hypothesised that a cat's purr can be used as a healing mechanism to offset long periods of rest and sleep that would otherwise contribute to a loss of bone density. The vibrations and contractions of a purr work during both inhalation and exhalation show a consistent pattern and frequency around 25 Hz; these frequencies have been shown to improve bone density and promote healing in animal models and humans"

Citation - Transmissibility of 15-Hertz to 35-Hertz Vibrations to the Human Hip and Lumbar Spine Rubin et al Spine, 28 (2003), pp. 2621–2627

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This post does not cite any references or sources. Please help improve this post by adding citations to reliable sources. Unsourced material may be challenged and removed.

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Welcome to Skeptics! Please provide some references to support your claims. What Wikipedia page? What scientists? The paper cited demonstrates no such thing. (To start with, it was on humans!) –  Oddthinking Aug 29 '13 at 16:32

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