You undoubtedly spend a lot of time petting and brushing your dog and know his body and hair quite well. It may surprise you the first time you see his hackles go up and wonder what is going on with him. His hackles are the hairs along his backbone that start in his neck area and extend along his spine up to his tail. When these hairs rise, it is called piloerection, with pilo meaning hair. This is an involuntary reflex typically triggered by some sort of arousal your dog is feeling and it is completely out of his control. This response is often seen as a sign of aggression but it is important to observe what else is going on with his body language to really understand what your pup is feeling. Putting his hackles up is a great way for your dog to tell you how he is feeling. In monitoring what is going on with him, you can help him handle tricky situations with more ease.

You have undoubtedly experienced the automatic response of goosebumps on your skin when you have had a surge of adrenalin in your body due to feelings of fear, anger, insecurity, or even excitement. Piloerection, or putting his hackles up, is the same phenomenon in your dog. The arrector pili are specific muscles under your dog’s skin that are attached to his hair follicles and they are communicated nervous energy by the sympathetic branch of the autonomic nervous system. Basically, his adrenaline triggers a "fight or flight" system response to feelings he is having. Other species, including cats, rats, birds and even humans experience the same reaction. Porcupines rely on this autonomic response for protection and to scare off possible predators. In dogs, this reaction traps air between the hair shafts and fluffs him up making him appear larger. All breeds experience this natural response to adrenaline surges, but in some, it is easier to see than on others. Breeds with longer and fluffier hair do not as easily show hackling, while breeds with stiff and short coats tend to show their piloerection more clearly. 

Breeds with longer hair show hackling more clearly in their shoulders and some breeds such as Poodles can often have piloerection with no one noticing. One breed, the Rhodesian Ridgeback, has permanently displayed raised hackles that is a prominence of his breed rather than a constant piloerection. Many people assume that "hackling" is a sign of aggression and that any dog with raised hackles is looking to fight. In fact, dogs that are raising their hackles are more likely feeling startled, fearful, lacking confidence, nervous, or even excited. Hunting dogs often raise their hackles when they are hyper-focused and pointing at a bird of prey. It is important to learn that all sorts of emotions can bring on the piloerection, and working with your dog through these feelings is essential to having him properly socialized.

While there is not a lot of research on the subject, trainers tend to agree that where the hair is raised, combined with other behaviors and body postures, can really give you an idea of what is truly going on with your dog. It is believed among dog lovers and trainers that when a dog has raised hackles across the shoulders and above the tail, but smooth down his spine, he is in a confused, ambivalent, or conflicted state. A dog in this mind frame can be reactive and a bit unpredictable. Having hair raised only along the shoulders spanning nearly eight inches across and about one quarter to one-third of the way down his back tends to indicate a dog that is experiencing low confidence and is nervous. Shedding is more common from dogs in this category too, also indicating fear. A thin line of hair extending down the entire spine, from shoulders to tail, often indicates a confident and perhaps aggressive dog. Trainers stress also looking at your dog’s body positioning. If his posture is stiff and continues to stiffen, he is most likely feeling tense and aggressive. Is his tail tucked under in fear, wagging with excitement, or high and stiff with aggression? Is your dog bowed low in play posture or is he low on his haunches as if he may lunge? Ears can also indicate his mood, in that they can be back, flat, up, or relaxed. Is his face relaxed or is he bearing his teeth or snarling? 

Regardless of what is going on with your dog and his hackles, you need to remain alert yet calm. Even a dog that is aggressive is often working from fear and needs you to make the situation safe. An aggressive dog needs to be removed from any social gathering that may give him the opportunity to harm himself or others. Work to distract him and lead him away until he can be soothed. However, if your dog seems to have his hackles raised because he is nervous he may just need you to support him through the social situation. A dog that is not properly socialized can become fearful around other people and dogs. Removing him will not help him to become socialized, and dogs that are not properly socialized are more prone to developing aggression. An experienced trainer can help you socialize your dog and decrease the chance of problems in the future.

When out with your dog, be aware of how the atmosphere and social surroundings are affecting him. If you see him raise his hackles, check to see what is immediately around him. It is important to note that the hair-raising takes about thirty seconds from his initial reaction but it can take up to two minutes to relax. If the dog’s hair is in the resting phase, known as the telogen phase, when the piloerection occurs, then the hairs will loosen and fall out. This is why dogs tend to shed a lot when they are highly excited or stressed. A dog raises his hackles, or the hair on his back, as an autonomic reaction to a surge of adrenaline. He may be excited, nervous, lack confidence, or feel confused.

A surprised dog can also raise his hackles. This response is completely out of his control, just as you having goose bumps is out of your control. When your dog raises his hackles, it is important that you remain calm and try to distract him from whatever is stressing his sensory system. If he appears aggressive, attempt to remove him from the situation. If his hackles are from lack of confidence or fear and require socialization, support him and work with a trainer if necessary.