Science indicates that purring can reduce pain in cats which is probably one of its purposes. Some scientists think that one reason for purring is that it heals the cat. The reasons why a domestic cat purrs is still under discussion but the best answer I have is provided by Dr Desmond Morris in which he says that purring “signals a friendly social mood, and it can be given as a signal to, say, a vet from an injured cat indicating the need for friendship or as a signal to an owner, saying thank you for friendship given” (Catwatching).
People associate purring with contentment in their cat companion. But it means more than that, as indicated. And does it help a cat heal? And do cats purr when they are in pain? This, too, is a subject under discussion. We don’t know, for sure, the answers to these questions.
However, it may be true. Let’s look at it this way: the feline purr is a low-frequency sound. It is a mellow and pleasant sound which is calming to jangling nerves in their human companion! Perhaps it also calms a cat in the same way.
But there may be a scientific basis for the healing power of the purr. I’m referring to the way a low-frequency sound may reduce the sensation of pain in a cat.
As it happens, there is a study on “The effect of low-frequency sound stimulation on patients with fibromyalgia”. Fibromyalgia is a very painful condition in people. It is often triggered by stressful events including physical stress or emotional i.e. psychological stress. Other triggers might be an injury or viral infection. Above all the patient suffers widespread pain, tingling in their feet or hands and depression. The general remedies are getting more sleep and exercise to try and reduce stress.
The study referred to was an attempt to find effective treatments for fibromyalgia. They subjected 19 female volunteers suffering from the condition to low-frequency sound stimulation. It’s believed that low-frequency sound can play a “regulatory function by driving rhythmic oscillatory activity”.
I’m not sure what that means but the scientists who carried out the study concluded that the low-frequency sound treatment “showed no adverse effects and patients receiving [it] showed statistically and clinically relevant improvement”.
In other words low-frequency sound can reduce pain in people. That’s my interpretation. I believe it is a reasonable argument to state that it is distinctly possible that one reason why cats purr when they are under stressful circumstances and/or injured is because it helps them feel better both in calming them and reducing the sensation of pain that they are experiencing.
Purring is a kind of music and it has been found that music can help to release endorphins, dopamine and serotonin and decrease cortisol levels. This also supports the possibility that cats purr to decrease discomfort and pain.
It should be noted that music can be a kind of medicine. It affects brain chemistry and has mental and physical health benefits on enhancing mood and reducing stress.
Conclusion: it is likely that one reason why cats purr when at the vets is because it reduces pain and calms them. This helps to understand why cats purr when apparently unhappy.