When a dog is relaxed, his fur is too. But sometimes a completely involuntary hair raising reaction based on a trigger or arousal can make the hair on their shoulders and back to stand upright and appear larger.
By understanding why this happens, it allows you to interpret your dog’s emotional state more accurately and respond appropriately to their needs.
Here’s why your dog's hair stands up when barking
A dog’s hair stands up while barking, it is commonly referred to as piloerection which simply means “raised hair” or the hackles raising, which is triggered by aggression, fear, excitement, display of dominance over other dogs and social signaling of possessive behavior.