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A Look into Dog Hackles

A black cat with raised hackles is a staple of Halloween decorations, but did you know that dogs have the ability to raise their hackles too? The action of raising hackles is known as piloerection, literally meaning raising of hairs. Cats are known to raise their hackles, but so do porcupines with their thick hairs when they're frightened by predators. In some sort of way, the action is similar to when we get goosebumps, and as the popular expression goes, our "hairs stand on end. " So let's discover some interesting facts about dog hackles and why dogs raise their hackles.

Skin anatomy and skin follicle, Wikipedia Commons Public Domain

Skin anatomy and skin follicle, Wikipedia Commons Public Domain

A Lesson in Anatomy

Dogs are equipped with hair follicles that are attached to special muscles called the "arrector pili" which are confined to the dog's neck, back and tail.

When the dog is in a normal, relaxed state, the hair follicles stay at a 30 to 60 degree angle compared to the skin.

Let the muscles contract though and those hair shafts will literally stand up, explains Karen L. Campbell, a board-certified veterinarian specializing in internal medicine and dermatology in the book "The Pet Lover's Guide to Cat and Dog Skin Diseases."

Getting Worked Up

dog raised hackles

Raised hackles in dog

The arrector pili muscles are innervated by the sympathetic branch of the autonomic nervous system.

In our canine companions, contraction of these muscles is elicited by the release of epinephrine as it occurs when the animal feels afraid or excited, further adds Dr. Campbell.

The contraction is involuntary, and thus, not under the dog's conscious control as it's part of the dog's fight-or-flight reaction.

It can also be seen in animals that are aroused, anxious, uncertain or surprised by the sudden appearance of an unexpected stimulus. An overstimulating play session may also cause raised hackles in dogs while playing.

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There are chances that based on the area of raised hairs, one may deduce information pertaining the dog's emotional state. Raised hackles by the shoulder area may denote fear, while hackles raised by the tail area may suggest confidence, and in both shoulder and base of tail, they may suggest an ambivalent emotional state and conflict, (Karen London, 2012).

Most likely, just as in the cat and in the porcupine, the action of raising those hackles has some adaptive function meant to make the dog appear larger than he really is.

But wait there's more! Alexandra Horowitz in her book "Inside of a Dog, What Dogs See, Smell and Know " on page 110, explains that those hairs may also release the odor of skin glands located at the base of the hairs.

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Raised hackles during rough play

Raised hackles during rough play

Not Necessarily Aggression

It's not correct to make unfounded claims that dogs who raise their hackles are aggressive. First of all, it's wrong to label dogs as aggressive from the get-go, as dogs aren't always in a constant state of aggression. It's more correct to say that dogs may act aggressively in certain scenarios versus "dogs are aggressive."

Also, one must identify the stimulus that triggered the hackles to rise in the first place and take note of the accompanying body language before drawing conclusions.

The fallacy of stating that dogs who raise hackles are aggressive is counterproductive, as it labels dogs through mere speculation and assumptions. If you are uncertain as to why your dog may raise his hackles, consult with a veterinary behaviorist.

Getting Warmed Up


The sensation of cold has been associated in several animals with the activation of the sympathetic nervous system causing the contraction of the arrector pili muscles.

The piloerection in this case is meant to trap air and create a layer of insulation. As the hairs thicken, the amount of subcutaneous fat also increases. In us humans, cold still triggers goose bumps, causing the characteristic bumps and the rising of the hair shafts.

Charles Darwin in the book "The Expression of the Emotions in Man and Animals " classified the appearance of goose bumps as a vestigial reflex though, consideringthat ithas lost its original function since we're no longer covered in hairs.

In dogs, Steven R. Lindsay in his book "Handbook of Applied Dog Behavior and Training, Procedures and Protocols" discusses about a possible interesting relationship between reactive emotional states and the process of heat production.

The findings of several studies conducted on rats found a correlation between psychological stressors and temperature elevations. These increases in temperature may therefore turn out being a useful, non-invasive tool for evaluating the presence of psychological distress in dogs, he suggests.

Did you know? You're not imagining things when you notice more hair loss in your dog during stressful situations. What happens is that hairs that are in the telogen phase (the resting phase) are more likely to fall out when the arrector pili muscles contract as it happens in stressful situations such as being at the vet, explains board-certified veterinary dermatologist Karen L. Campbell in the book "The Pet Lover's Guide to Cat and Dog Skin Diseases."

idea tip


  • Alexandra Horowitz in her book "Inside of a Dog, What Dogs See, Smell and Know", Simon &Shuster, Inc, New York, Ny
  • Darwin, Charles. (1872) The Expression of the Emotions in Man and Animals John Murray, London
  • Karen L. Campbell "The Pet Lover's Guide to Cat and Dog Skin Diseases"Elsevier Health Sciences, 2006

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