Why Do My Dog’s Hackles Stand Up on End?

January 18, 2023

By: Kristyn Savage, PhD, CAAB, BCBA-D
Dog staring at other dogs and people

Common body language when I observe dogs in various situations is a dog’s hackles, or fur, standing up on end. Technically this is referred to as piloerection and is due to an involuntary response. A dog’s fur follicles send a message to their parasympathetic system when they are startled or threatened, aroused, or for some when they wake up, or there is a temperature change. 

When might this behavior occur?

Dog engaging in precursor behavior

When startled or threatened

The most common and obvious time a dog’s hackles stand up is when they are startled or threatened. The trainers I work with see this body posture nearly every day when working with reactivity cases. Piloerection, in this context, can serve as a precursor to barking, lunging, or biting. The stimulus (i.e., a strange dog or person) usually starts out of sight and appears suddenly, at least from the dog’s perspective. Once the stimulus is within sight, the dog begins staring with their mouth pulled tightly closed toward the stimulus. To learn more about precursor behaviors, check out my blog, Identifying Body Language in Dogs. The dog’s behavior escalates if the stimulus moves closer to the dog and is reinforced if the stimulus moves away. 

When they are aroused

The second most common occurrence of a dog’s hackles standing up I observe is when a dog is aroused. This occurs during a greeting with another dog and play. During greetings, dogs circle each other, smelling their friend’s hindquarters. Often a dog’s fur stands up on end, and their tail raises and becomes stiff or wags quickly. This is normal behavior; owners can help keep the greeting positive by keeping a loose leash (or no leash) and praising their dog. Tight leashes, restraint, and tense silence make the encounter less friendly, and a fight can erupt. 

When waking or exposed to temperature changes

Lastly, and often in a way that confuses owners, dogs’ hackles stand up on end when stretching, generally after several hours of sleep. Dogs seem to be shaking off and waking up. Their fur stands on end as their body prepares for the day’s action. Similarly, dogs show piloerection when moving from one temperature to the next and generally after exposure to colder temperatures. 

Like so many other behaviors, piloerection is part of a more extensive collection of behaviors deemed body language. With every different body posture or behavior, a more comprehensive observation must be made to determine the reason behind the posture.  Instead of taking a single snapshot of one body posture, it is important to observe several postures across a few seconds and consider any other environmental variables. The immediate environment, time of day, and who is present are all factors I consider as I observe a dog’s body language, and piloerection is no different!