When I sit down to write about this controversial topic I am cautious. These devices can be very polarizing and produce strong opinions in the dog training industry. Many owners use these devices because they've been told to use them by a trainer. Others use them because they haven't been able to find a better option. Whatever the situation, I never judge a dog owner for doing the best they can with the skills and tools they have been given to work with. Most people have the best intentions for their dogs and will do whatever is necessary to control problem behavior. Especially when that problem behavior has caused injury to person or animal or poses a risk to the dog's safety.
Shock collars, pinch collars, prong collars, choke collars, electronic fences, bark collars, etc... these little devices are everywhere. They're on every store shelf. They have the wallet to advertise to the people in need of help. Then they come in with guarantees and promises as if they will miraculously change the unwanted behavior you are seeing in your dog. They produce fast results and when your are facing serious behavior problems at home a fast solution can seem like a godsend.
However, there are some serious negative consequences that can come with aversive devices in training that often go unmentioned on the packaging. So let's talk about them: the good, the bad, and the ugly.
When we talk about the science behind training it is all based on operant conditioning. Operant conditioning sounds complicated but when broken down it's really very simple: all animals, including humans, learn through consequences. Those consequences can be positive, such as getting a treat for good behavior, or they can be negative such as receiving a painful zap from a shock collar for bad behavior. If a behavior gets a positive consequence, the behavior is likely to be repeated. If the consequence is bad the behavior likely will stop.
Operant conditioning can be broken down into four separate quadrants. Positive reinforcement, negative reinforcement, positive punishment, and negative punishment.
The word positive simply means adding a stimulus, while the word negative refers to removing a stimulus, or taking something away. The words reinforcement and punishment also have scientific definitions.
Reinforcement is defined as a consequence that follows an operant response that increases (or attempts to increase) the likelihood of that response occurring in the future.
Punishment is defined as a consequence that follows an operant response that decreases (or attempts to decrease) the likelihood of that response occurring in the future.
When we talk about aversive devices, we are usually referring to two of the quadrants: Positive Punishment and Negative reinforcement.
In psychology, an aversive is defined as unpleasant stimuli that induce changes in behavior via negative reinforcement or positive punishment. By applying an aversive immediately before or after a behavior the likelihood of the target behavior occurring in the future is reduced.
Let's talk about some psychology experiments that were done several decades ago that taught us a lot about the pros and cons of aversives. We will start with the Little Albert Experiment. 
In the early 1900s, a researcher by the name of John B. Watson conducted an experiment to see if he could condition a fear response in humans.
He used a 9 month old emotionally stable baby for the experiment. We don't know anything about the baby other than his pseudonym - Little Albert. Albert was given a battery of baseline emotional tests: the infant was exposed, briefly and for the first time, to a white rat, a rabbit, a dog, a monkey, masks (with and without hair), cotton, wool, burning newspapers, and other stimuli. Albert showed no fear of any of these items during the baseline tests.
These experiments went on for two months and eventually the baby was moved to a controlled environment. He was placed on a mattress and given a white rat to play with. Each time the baby touched the rat, Watson would hit a suspended steel bar with a hammer behind the child. Albert would then cry and become afraid. Each time he did it the baby became more afraid of the rat until he wanted nothing to do with it. Eventually, upon seeing the rat, Albert would immediately cry and attempt to crawl away. Watson had accomplished the task of creating an aversion very quickly. However, Watson also noticed some unintended consequences of the experiment. The baby also became afraid of anything that was white and furry. Watson noted that the baby reacted with the same fear to a rabbit, a dog, a white sealskin coat, and even a Santa Clause mask. We call these fears associations. And the intended association with the rat was generalized to all white furry animals.
So lets look at this experiment if we were conducting a similar experiment with a dog. Let's use a pinch collar as an example. My dog likes to pull so as a solution to the pulling I've decided a pinch collar seems like an appropriate device to stop the pulling. The dog pulls against me, I tighten the pinch collar around the dog's neck. The pinch collar creates a pain that is applied consistently until the dog stops pulling and then the collar is released. This is a negative reinforcement.
But what is the dog pulling toward? If the dog is pulling toward another dog and they are greeted with pain I am taking a huge risk. There is a 50% chance the pinch collar will work and my dog will stop pulling on the leash. However there is also the 50% chance that my dog will form a negative association toward the other dog (and given that at this point the collar has probably been used repeatedly for weeks or month) he will likely form that association with all dogs. I have now unintentionally created a potential fear of dogs. When fear enters the training game we run into the development of more dangerous behaviors such as reactivity and aggression. Reactivity and aggression can be challenging to treat and can often take months if not years to recover from. And sadly, because of the way fear works in the brain in rare circumstances it cannot be undone.
What if the dog is pulling toward a school bus full or children, or an old person, or a baby stroller, or anything else outside the house that seems new and interesting. All of these things can become scary. And in a worst case scenario everything outside the house becomes scary.
There is also the risk that the dog will make the association between me and the pinch collar, since I'm the one holding the leash. I run the risk that my dog will eventually get sick of the repeated negative reinforcement and will turn on me. Unfortunately this is an all too common scenario.
Shock collars usually have even worse fallout.
I was an e-collar trainer for a period of time and can site my own experience with these devices. Most trainers that use them will tell you that they are effective WHEN USED PROPERLY. But is there a proper way to use pain to train dogs? Well, let's look at the science.
In 2014 a study was done that examined the consequences and efficacy of using shock collars as a training device in dogs.
This experiment was done using 63 dogs referred to trainers for recall related problems. These dogs were assigned to one of three Groups:
Group A was trained by industry approved trainers using e-collars.
Group B was trained by the same trainers but without use of e-collars
Group C was trained by members of the Association of Pet Dog Trainers, UK again without e-collar stimulation
The dogs received two 15 minute training sessions per day. Training sessions were recorded for behavioral analysis. Saliva and urine were collected to measure cortisol levels.
The researches noted on preliminary studies that there were negative changes in dogs' behavior immediately on application of electric stimuli, and the dogs showed elevated cortisol levels even after the application of the shock.
In contrast, in the subsequent larger, controlled study, trainers used lower settings with a pre-warning function and behavioral responses were less marked.
Nevertheless, Group A dogs spent significantly more time tense, yawned more often and engaged in less environmental interaction than Group C dogs. Salivary cortisol in Group A dogs was not significantly different from that in Group B or Group C, though Group C dogs showed higher measures than Group B throughout sampling. Following training 92% of owners reported improvements in their dog's referred behavior, and there was no significant difference in reported efficacy across Groups. Owners of dogs trained using e-collars were less confident of applying the training approach demonstrated.
This study confirmed that there is no benefit to training with an e-collar, dogs trained in an e-collar showed higher stress levels that remain elevated even after the shock has been applied. And the dogs trained using only positive reinforcement showed the same behavioral improvements as the dogs trained in e-collars with overall lower stress.
A similar study was repeated that found the same results. That study can be accessed here.
Over the last 50 years dozens of studies have observed animal responses to shock. Most of these studies have offered the same result. A unexpected shock can lead to an aggressive response.
In the 1960s and 1970s several studies were done. One particular study observed the response of squirrel monkeys to a tail shock. If a brief electric shock was delivered to a squirrel monkey, the subject would vigorously attack both animate and inanimate objects.  If initially a neutral stimuli repetitively preceded the shock, they would also attack. This showed that aggressive behavior can become an unintentionally conditioned response with the use of a shock.
Another study was performed in 1981 on lab mice that showed an aggressive attack response to an electric shock. When shocked the male mice were prone to attack each other. The study also showed that more dominant male mice would often attack their mate when exposed to electric shock. 
In 1969 an experiment was done that showed shocks were followed by an aggressive response in rats. When the shocks stopped, the aggressive behavior ceased. 
Another study involving paired rats showed an aggressive biting response to being shocked while they were restrained. The present study developed a procedure whereby individual rats given shocks might bite an inanimate target object. Unavoidable shock was delivered to the rat while it was restrained in a position close to, and facing a target object. Biting of the target was recorded automatically. Shock caused the rat to bite metal, wood, or rubber targets. Biting was most frequent immediately after shock and decreased as a direct function of time since the shock. Almost every shock produced biting and the behavior continued as long as the shocks were delivered. Biting ceased within and between sessions when shocks were discontinued. These results show how the pain-aggression relation can be studied objectively with rats. 
Shock collars can lead to aggression. We know this, after decades of research. We've observed this not just with dogs but with a variety of other species, including humans. So why is it still acceptable to use them on dogs?
Well there are several unfortunate reasons but the main reason is that the dog training industry is not regulated. There are no current regulations or requirements for what is acceptable in the realm of dog training in America and there are no current regulations on animal welfare in terms of what is available on the market. So retailers are allowed to sell any device they want as long as it doesn't appear to physically injure a dog. Emotional injuries are not taken into account. We are just now starting to acknowledge that animals are emotional creatures. And emotions affect behavior.
Another reason is that on the surface they appear to work. A pinch collar often will stop pulling. But the pulling stops because it hurts. A choke collar can stop pulling. But a choke collar can also be a death sentence for a dog. Dogs die on choke collars far too often. Perhaps these deaths are due to misuse but why would anyone choose to use a device that has the potential to be lethal if not used correctly?
There are other negative health consequences to using these devices. In 2014 a dog was killed as a result of a choke collar that got tangled while playing with another dog .
In 1994 a series of choke chain related deaths led to a move by the Humane Society of Utah to begin advocating for their dangers .
A dog died in a Petco dog training class from a choke collar. The cause of death was "post-obstructive pulmonary edema (POPE) as a result of a 'choke' or 'restraint.'" 
Pinch collars and choke collars have been linked to a variety of health conditions. Repeated corrections done "correctly" to the soft tissue of the dog's neck can cause tracheal damage, soft tissue damage, and even neurological problems. 
There are better options. If you're experiencing problem behaviors with your dog, reaching out to a qualified force free or positive reinforcement trainer or behavior consultant is the best option. They will be able to advise you on what approach to take that will benefit both you and your dog and strengthen your relationship without the potential risks of aversive fallout.
We owe it to our dogs to be kind. They come into our lives and are expected to adapt to our lives and that can be a struggle. It takes time and patience. But in exchange for the hard work and patience we put in, we get an unbreakable bond and relationship based on trust and love. And that's why we get dogs isn't it? Because there is just something really special about them.