Ask A Vet: Why Does My Dog’s Hair Suddenly Stand On End?

Have you ever been walking your dog when suddenly they stop, and all the hair along their back stands on end? This fascinating phenomenon is called piloerection, and it’s mediated by tiny muscles in the skin called arrector pili. While humans also experience piloerection, we typically refer to it as “goosebumps.”

Just as we might get goosebumps when we’re cold, scared, or experiencing a strong emotional reaction, dogs’ piloerection can occur for similar reasons. However, unlike us, dogs have no conscious control over this reaction—it’s an automatic response triggered by their nervous system.

Piloerection serves several purposes, depending on the circumstances. In cold weather, the raised hair can increase insulation by trapping more air close to the skin. This layer of air acts as a barrier, helping to retain body heat. It’s a mechanism that humans mimic with puffy winter parkas and down-filled coats, which rely on trapped air for warmth. If you’re out on a chilly day and notice your dog’s hair standing up, it might be their body’s way of conserving heat.

On the other hand, if your dog is walking with you on a mild day and suddenly raises the hair along their back, the trigger is more likely to be emotional—fear, surprise, or heightened alertness. When a dog experiences these emotions, their body releases adrenaline, which causes the arrector pili muscles to contract and lift the hair. Experts believe this reaction creates an optical illusion that makes the dog appear larger and more intimidating to potential threats. In nature, this could deter a predator or rival, helping the dog avoid a confrontation.

Although piloerection itself is harmless and temporary, it can provide important clues about your dog’s emotional state. A dog with raised hackles may be feeling stressed, anxious, or reactive. It’s crucial to be mindful of their body language during these moments. Avoid startling or touching them, as they might react unpredictably. Instead, give your dog space and allow them to calm down. If you’re in a situation where your dog’s hackles are up because of a perceived threat, calmly retreat to a safer environment to help diffuse the tension.

Finally, remember that your dog’s piloerection can also signal that they’re feeling cold, especially during winter walks. Dogs acclimated to a domestic lifestyle often have less tolerance for cold weather than their wild counterparts. If you frequently notice your dog’s hair standing up during outdoor activities in colder months, consider investing in a well-fitted dog coat to keep them warm and comfortable. Just as you bundle up against the cold, your furry friend will appreciate the extra protection.

Piloerection is a natural and harmless response that can tell you a lot about what your dog is feeling in the moment. Whether it’s triggered by cold, fear, or adrenaline, it’s a reminder of your dog’s instincts and their need for comfort and security. Paying attention to this and other subtle cues can help you better understand and care for your canine companion.