Some dogs are simply touch-sensitive. Many do not take well to being inspected by the vet or brushed by a groomer. Always make sure there is nothing physically wrong that is causing the dog pain.
Cautionary Tale
Miniature poodles have curly hair and not fur, and this coat does not shed. A client of mine used a shedding brush intended to shear shedding fur from short-coated dogs. The brushings were painful, and this dog was now afraid of all brushing.
Redemption Tale
We purchased the appropriate brush and got to work. To desensitize the traumatized poodle, I put her on leash while holding a fistful of treats. I let the dog nibble from my hand as I merely showed her the brush for a few seconds. I then touched her with the smooth backside of the brush as she continued nibbling from my half-closed fistful of small treats. The dog was reactive to a degree, but each session lasted maybe two minutes, with ten-minute breaks until I was able to brush her with the smooth side. In the attempts that followed, I managed a few strokes without the treats. I would say it was a little over an hour before the reactiveness was gone and we were able to easily brush the dog’s hair.
Any touch sensitivity that a dog may exhibit can be treated in this fashion so long as one is patient. In many cases, toys will work far better than treats. You need to be ready to experiment.