What does piloerection in dogs indicate?

Piloerection in dogs refers to the phenomenon where the hair on a dog's back stands up. This is an involuntary response that occurs when a dog is feeling threatened or frightened, often associated with a fight-or-flight response. When dogs are fearful or aggressive, their body instinctively prepares for potential confrontation or escape, and piloerection is a physical manifestation of that emotional state.

This reaction serves to make the dog appear larger to perceived threats and can also be a sign that the dog is on high alert. In contrast, other emotional states such as calmness, excitement, or happiness do not trigger this response; rather, they are typically accompanied by relaxed body language and posture. For instance, a happy or excited dog often displays loose and wiggly body language instead of the raised hairs associated with fear or aggression. Understanding piloerection helps in interpreting a dog's mood and intentions, which is essential for safe interactions.