Have you ever been walking your dog when suddenly he stops and all the hair along his back stands up?
This process is called piloerection and it is mediated by tiny muscles in the skin. People experience piloerection too, except we call it “chill bumps.” We can experience them when we are afraid, like in a scary movie or when we are actually chilled. Your dog’s piloerection can occur from the same stimuli. Contraction of the muscles that pulls the hair up is an automatic response. Your dog does not mentally decide to raise the hairs (and neither do you).
The lifting of the hair in response to cold is thought to increase the insulation factor of the hair by making room for more air among the hairs to prevent heat loss. The same theory applies in winter parkas or down coats which are puffy and air filled and keep the wearer very warm.
If your dog is walking along with you and is not cold, but suddenly the hair along his back raises, the cause is more likely to be fear or surprise. Adrenalin, too, can cause the muscles to contract. Experts believe that the optical illusion provided by raised hair is designed to make your dog appear more formidable to a potential enemy. Whichever the cause, cold or fear, the piloerection is harmless to your dog and his hair will return to normal once the moment had passed with no permanent change.
Be aware that a frightened dog may be more reactive than normal, so when he is tense with his “hackles” up, it is not a good time to touch or startle him yourself. Retreat may be a better choice to defuse a potentially volatile situation and remember, your dog is acclimated to his domestic life with you so if you feel cold, he probably does too. If you notice his hair is standing up frequently when you are outside in the cold, he might enjoy a winter coat.
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