We love to pet our cats. We love stroking the fur behind their ears, the silky fur on their backs, the soft, thick fur on the tops of their heads. We keep doing it not just because we love it, but also because we can see from our beloved cats' reactions that they love it too. Now, scientists think they know why cats, and many other animals (including people) just love being pet.
Mammals (and possibly birds) apparently have special nerves in hairy skin that send pleasure signals to the brain. The nerves, called C-fibers, only seem to exist in hairy skin and may explain why so many furry animals love being stroked. They're a very small subset of neurons that exist in all mammals.
This may have evolved because mammals and birds needed ways to clear their fur and feathers of dirt, ticks, fleas, and more. If stroking and grooming feels good, animals are far more likely to do it. What's more, they're far more likely to do it to each other, which is more effective than each individual grooming themselves.
Recently, a study surfaced that media everywhere misinterpreted as saying that petting your cat actually stresses her out. However, the researchers clarified their position to say that they were studying multi-cat households, and looking to see whether cats living in such households were more stressed than cats living in single-cat households.
They believe that the confusion came when they said that some of the cats in the study only tolerated being pet, which increased their stress. One of the study's authors said, however, "Cats are in no way generally stressed when they are stroked. It depends much more on the situation and the character of the individual animal."
So go ahead and stimulate those C-fibers, if you know your cat enjoys it. Now, at least, you know why, and you also know you aren't stressing her out.