Karen B. London
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What’s going on when a dog does this?

“His hackles went up. What does that mean?” It’s such a great question and one that I hear from clients regularly. When the hair on a dog’s back goes up (technically called piloerection), it’s usually a sign that the dog is aroused or excited in some way. It is an involuntary reaction, just like the goose bumps we humans get, so it’s important not to have any expectation of a dog being able to control it. While sometimes aggressive dogs do exhibit piloerection, it is not true that it’s necessarily a sign of aggression.

Data are limited on this phenomenon, but as an ethologist trained to observe animals and their behavior, I have noticed some things about it. Based on my experience with many dogs over the years, it seems that different patterns of piloerection are associated with different behaviors, probably because they are associated with different internal emotional states.

Some dogs exhibit a thin line (at most a few inches wide) of hair all along their back to the base of the tail. I associate this pattern of piloerection with a high level of confidence and in my experience, these dogs are more likely to go on offense and behave in an aggressive way than other dogs.

Another common pattern of piloerection is a broad patch of fur (up to 8 or so inches wide) across the shoulders, which does not run more than one-quarter or one-third of the way down the back. I associate this pattern of piloerection with low confidence and I often find that these dogs are somewhat fearful.

The most confusing pattern is when a dog exhibits a patch of hair that is raised at the shoulders and another raised patch at the base of the tail. The hair in between along the back is not raised. This pattern of piloerection often occurs in dogs who are in an ambivalent emotional state and feeling conflicted. Many of the dogs who show this pattern are somewhat unpredictable in their behavior and inclined to be more reactive than other dogs.

Of course, there are many exceptions, but these generalizations apply to the majority of dogs that I see. What have you observed about dogs and piloerection?


Karen B. London, PhD, is a Bark columnist and a Certified Applied Animal Behaviorist specializing in the evaluation and treatment of serious behavior problems in the domestic dog.

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Submitted by MichelleH | April 4 2012 |

My 2 year old Lab, Sophie often has her "hackles" raised when she is excited. She is the odd type with a patch at her shoulders and at the base of her tail. When Sophie is excited about something, a visit from a family member or friend or a play date with a canine buddy it happens. She looks ferocious with her fur raised up, but she's as gentle as a lamb and has never been aggressive toward any animal or person.

Submitted by Anonymous | April 4 2012 |

My dog does this every day towards the dog next dog. She has no dog friends b/c she is the stereotypical bully: low self esteem and always on the offensive. As a rescue we have only assumed that she was not socialized at all and we're left with a dog that can only have people buddies.

Submitted by Cindy | April 4 2012 |

My 19 month old female lab exhibits that last pattern (raised hair at shoulders and tail only) every time we go to the park. She only does it upon greeting an unknown dog during the first few minutes we are at the park. She tends to be a little shy despite lots of socialization work that we started when she was 14 weeks old. I have always attributed her "raised hackles" to shyness and insecurity. It seems she is trying to appear larger until she gets into the park and begins playing. She has never shown any aggression towards any dog or person.

Submitted by La Trenda | April 4 2012 |

So what about the dogs who have raised, wide hackles all the way down from shoulders to butt and in the middle?

Submitted by gregk9 | April 5 2012 |


Submitted by Karen London | April 5 2012 |

I've seen this pattern too rarely to be able to make any generalization about it other than to say I think it indicates quite a high level of arousal, whatever the cause of that arousal might be. Also, some of the dogs with this pattern that I can remember were dogs with long coats, so sometimes the pattern of the hair looks exceptionally wide even though the area of the skin that is affected is not quite as wide and may be similar to the narrower strip that is more often seen. I'd love to see more dogs with this pattern or hear from more people whose dogs show it. Then, it would be easier to make conclusions about it. Great question!

Submitted by Anonymous | April 29 2012 |

I was very glad to come across this post after our local shelter shared it on their Facebook page. Our dog is Lab/Akita and demonstrates this anytime he is excited. He does it in the back yard when he smells deer, other dogs... pretty much anything besides himself. He does it quite often when meeting new dogs as well. From what we have observed in our 2 years together is that he is just very excited and happy.

We had two neighbor dogs come up and sniff at him then when we turned to walk home they attacked his ankles and had him on the ground. He turned and ran home (thank god) and ended up with 5 puncture wounds. We have not had any other incidents together. I was worried that the Hackles might have been aggression, but we haven't seen that.

As for leash behaviors that others have posted about, we always just let go of the leash if other dogs are unleashed and come up to him. That way we don't get tangled in w/ the whole sniff each other routine and after our incident mentioned above it allows for him to go away if anything were ever to happen again. He's at our ankles all the time to I can just pick up his leash after the dogs get their fill of sniffing at each-other. It is pretty frustrating to have other dogs come at him though.

Submitted by gwen kissel | July 6 2013 |

My lab/shepherd mix is 8 months old, When he is agitated and very angry his heckles from top of head to tail very wide goes up. I noticed it when we were in the front yard and the neighbor was out in his yard and KC started to bark at the neighbor like he would rip him apart, other times at night when he hears something outside and he runs from back yard to front door trying to get at whatever is out there, barking aggressively. He is very protective of me and he will not let any stranger approach me. He will remain quiet at my side but his heckles start to go up. Sometimes just his shoulders but other times the full head to tail. He reacts to the doorbell the same way. I do not think he is showing fear, because he tries to get between me and whatever is on the other side. but he is a gentle dog.

Submitted by Brute's Mom | April 4 2012 |

My GSD/Siberian Husky mix Brutus gets the confusing pattern. Shoulders and base of tail only. He is not "dog Aggressive" per se, but does not care for most dogs. Not reactive, we can walk by dogs barking at him and he will to me as if to say, "whats up with that?" He has had a couple of dog friends (esp. an older husky/golden mix) but does not like dogs running up to him. I work with dogs (have worked in grooming, training and now as a dog walker/pet sitter) and he was exposed to plenty of dogs and humans on a regular basis. he is polite on walks and when hiking he knows when we meet others on the trail to move to the side with me and wait. Our only problem is with those who let their dogs off leash in areas where it is supposed to be leash only :>(
He DOES NOT like dogs running up to him and will snarl and growl when they do.

Submitted by Anonymous | April 7 2012 |

Thank you for posting this about dogs on leash not liking dogs off leash running up to them. I don't know how to educate their owners, but it is a potential real problem. The worst people are the ones that justify it with "my dog is friendly". That is not the point. I think dogs on leash meeting dogs off leash feel somewhat trapped, and no one (people or dogs)likes someone running up to their face.

Submitted by Frances | April 4 2012 |

You have made me realise that this a signal I simply do not see in either of my dogs - one is a poodle, and it is lost in the woolly coat, the other is a papillon, and again it is almost impossible to tell because of the full, drop coat. There must be many, many dogs where piloerection is difficult, if not impossible, to see - which makes me wonder if it is a signal other dogs read, that some dogs cannot display?

Submitted by Anonymous | April 5 2012 |

Great post--thanks! My dog's fur often goes up on her shoulders during play. I figured she was just excited as she has not exhibited any aggressive behavior.

Submitted by Anonymous | April 5 2012 |

I noticed that when my dog (a pit mix) plays with the female american bull terrier next door, that her hair is up on her back. But after reading your article, I think that it is from excitement, not aggression. They play together almost every day and are very good friends. My dogs have never had their hair up from what I've seen.

Submitted by gregk9 | April 5 2012 |

I'm going to dissagree somewhat.

Hackles between the shoulders = dominance/ confident arousal - something to that effect.

Hackles up all along the back to the base of the tail = fear

Agreed that hackles up at the shoulders and the rear end = ambivalent state of mind but they're no more reactive than the other examples

Submitted by Dennis Fehling | April 5 2012 |

you are kidding right about the dominance thing? How can you possibly tell that a dog is being dominant by the hackles being raised on their shoulders. I am sure you got this from some TV Trainer. This is such an outdate frame of mind and is why there is so much conflict between dog and man...

Submitted by gregk9 | April 10 2012 |

No, not kidding. Learned this from Lee Mannix, not a TV trainer. Also verified it observing my pack of 12 dogs and working with others. It's not etched in stone. There are exceptions but in general, I've found this to be accurate.

Submitted by Naughty Dog School | April 5 2012 |

To Dennis Fehling who posted the comment on April 5, 2012.

OMG! You are so funny. With all due respect to whoever you are (I have never heard of you before) I am not sure who you think you are writing back to when you posted your comment but it is not like Karen London is just some pleb that watches stupid dog training shows on TV and then recites them.
SHE is the one that we as Behavioural Trainers/ Behaviourists/ Behavioural Consultants and the like study and wait for new information from (based on science and research)!
You should probably research who she is before saying something so silly!
Although I am well of aware of the piloerection discrepancies myself, it was great when a client sent me this to back up what I had just explained about her dog's behaviour the evening before!
Thank you for sharing your knowledge and personal observations Karen.

Submitted by North Idaho Dog Fun | April 5 2012 |

Just this morning our neighbor's dog was in our yard when I went outside. When the dog saw me her hackles (full back) went up, she hunched over, and went back to her house with her head lowered...

It seems to me that there is always an element of fear when there is piloerection. Perhaps the amount of hair being raised is related to the amount of uncertainty/anxiety being experienced?

Thank you for posting on this! It is great reading everyone's comments on what they have seen with their dogs!

Submitted by wendy | April 6 2012 |

It occurs to me that this hair-raising behavior makes the dog appear larger than s/he is in reality. Maybe it's related to a fool-the-eye with appearance kind of thing -- "I'm much bigger than you thought so please back off."

Submitted by Elaine | April 1 2014 |

Are there some breeds that are more prone to this? I have a rescue dog who is very sociable and does this when she is excited and happy! She has ripply hair in the middle of her back and this is the hair that is raised.

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