A dog's hackles consist of the hairs along the dog's backbone. They generally start from the neck area up to the tail. Such hairs have a piloerection function, meaning that they have a tendency to raise under certain circumstances. All dog breeds have this feature, however, in some dogs the hackles may not be easy to see as in others (dogs equipped with long haired coats). The effect is more pronounced on the shoulder area because the hair in this area is much longer.

The dog's hackles may raise from the neck up to the tail or they may simply just raise in the neck area. The function is to allow the dog to appear larger, taller and therefore more intimidating that it is. This is a ''fight or flight'' response triggered by adrenaline and similar in some way to the function of fish that ''blow'' themselves up to three times their size to look much bigger in case of a fight. This is also seen sometimes in cats that are startled by something, simply think the classic posture of a ''Halloween Cat''.

The hackles may raise for various reasons. The most common causes are fear and aggression. This behavior is often seen in young dogs that are unsure of their environment and are unsure on how to react. Hackling in dogs may be also someway similar to a human getting goosebumps.

According to the book ''Dog training for Dummies'' by Jack and Wendy Volhard, a dog with its hackles lifted from the neck to the tail is often sign of insecurity along with ears pulled back and tail tucked in, whereas. when the hackles go up only near the shoulder area this is sign of confidence. The ears are also erect, the tail is held high and the ears are erect.

However, in many cases, the aggressive stance is only a bluff. Most dogs are simply fearful but will become truly aggressive if cornered or forced to deal with its fear. If one thinks about it, truly dominant dogs will not need to resort to piloerection to look bigger because their confidence is boosted enough.

Sometimes, dogs may raise their hackles when they are overexcited and aroused rather than fearful. Generally, the meaning of raised hackles is determined by looking at other body language rather than focusing on the hackles alone.

Among dog breeds, the Rodesian Ridgeback displays permanently raised hair on their backs. This is not to be confused with raised hackles, this is just a typical feature of this dog breed.

If a dog owners notices his dog displaying raised hackles, the dog should be distracted from the source and taught more acceptable non -threatening behaviors.This nervous posturing should be avoided. If the dog is acting from fear, he should be calmed down (without resorting to petting, cuddling or soothing while the dog is in this state of mind).

A good way to accomplish this is by having the dog focus on some obedience commands. The dog handler should always be calm otherwise the dog will perceive nervousness, further exacerbating the fear. 

Meeting a stranger dog with its hackles up requires maximum caution. Do not stare the dog in the eye and simply back away slowly without turning your back to the dog. Running would further exacerbate the dog's aggression.