Understanding Reactive Behaviour13 February 2026

The definition of a reactive dog is one that will overreact in certain situations or stimulus.

An example of this could be a dog seeing another dog across the street, a person wearing a uniform such as the post man, a cyclist, or even a stationary object. These are known as ‘Triggers’ and a reactive response to seeing a trigger if often displayed by the dog’s behaviour, such as whining, barking, growling, and lunging. Often owners and passers by may feel the dog is being aggressive, with the owner punishing the dog possible through embarrassment which can escalate the fear, and the dog’s response to punishment potentially progresses to an even higher emotional response such as a bite.

However, reactivity and aggression are not the same. Reactivity can develop from birth, an example of this could be due to an irresponsible breeder, who simple does not care about the mother or the puppies. A pregnant dog that is subjected to stressful conditions and poor diet can develop a poor immune system and mental health issues, a chemical reaction to stress, is a release of adrenaline and cortisol (stress hormones) into her system. Once this builds up and continues daily her body cannot protect her placenta, so the chemicals release into the puppy bloodstream. When they are born they are already in an elevated level of stress.

Once the puppy is born a critical socialisation period begins between 6 and 14 weeks, this is known as the first fear period. Currently the mother and siblings are learning from each other through, play, grooming, and importantly touch. At this stage handling is important, and exposing the puppies to different textures, sounds, a variety of experience for everyday life in a home environment. This socialisation must continue once the puppies move to their new home, it is crucial this is done carefully, introducing new experiences positively. A traumatic experience at this time can have life long lasting effects.

The second fear period between 6 and 14 months, may show signs of lost confidence and more fear in certain situations it is vital to take things slow and remove the dog from the situation they appear fearful of. Offering support and encouragement is crucial. Avoiding ‘Trigger stacking’ where the dog is exposed to fearful situations daily. The sympathetic nervous system kicks in, and the dogs goes into survival mode, glucose is released for more energy, adrenaline is produced, heart rate increases the dogs is in survival ‘Flight or Fight’ mode. They become unable to listen.

The difference between a reactive dog and aggressive dog

The reactive dog is looking to increase distance from the trigger while aggression is generally moving forward with the intent to harm if necessary.

An aggressive dog is a dog that potential has experienced a traumatic event, a dog which has been punished for being fearful, or no socialisation.

Their communication through body language has been ignored, lip licking, tail tucked, yawning, barking, growling, ears flat are all signals we need to understand that the dog needs help. Ignoring this the dog will have no choice but to escalate their discomfort, from barking and growling to snapping or a bite potentially causing a severe injury. Territorial aggression, resource guarding, dog to dog, dog to human, medicated related aggression and littermate syndrome are all serious, if they are ignored and punishment is used. Aggression can also be down to genetics, passed down through the generations, breed specific training, aversive training technique's. An undiagnosed medical condition. This list is not exhaustive.

How we can help our dogs

It is crucial not to punish a dog for their reactive response to a trigger, instead advocate for them, get help from a behaviourist who can put together a behaviour modification plan, using positive reinforcement. Techniques such as Tellington Ttouch for calming can be introduced to the dog at their pace. Even taking a break from walks and implementing, enrichment, pattern games, scent work. This list is not exhaustive. Crucially not putting the dog in scary situations is important and advocating for them rather than blaming them. It’s important not to blame yourself either it can be incredibly stressful for both human and dog, seek help.

dog making eye contact with owner