We all know the most important things that determine the level of aggression in a dog is how they’re raised, trained and cared for. That said, a large study of over 9000 dogs has determined aggression towards humans can have multiple reasons behind it. Many previous studies have arrived at similar conclusions, but not all of them agree.

It’s difficult to draw conclusions from studies like this because there are so many variables that could impact the perceived results. It’s further complicated by the fact that we can’t simply ask a dog why she’s so grumpy or if she’s in pain. Breed aggression, for example, might really be due to the pain of a genetic illness that’s also associated with the breed. However, if we understand where aggression might be coming from, there’s a better chance of using the right method to address it or avoid it entirely.

What Increases the Odds of Canine Aggression?

The following conclusions are true of this particular study. It doesn’t mean all dogs that fall within these categories will be aggressive. It’s more of a heads-up so you can be on the lookout for potential problems, and deal with them accordingly.

Fear & Anxiety

In this study, as well as previous studies, fearfulness and anxiety had the strongest association with aggression.

“Fearful and noise-sensitive dogs have been found to behave more aggressively toward unfamiliar people than dogs with no anxieties. In the study of Dinwoodie et al., the dogs with a fear/anxiety problem had more biting incidences than other dogs, and they also found remarkable comorbidity between fear/anxiety and overall aggressive behaviour.”

Another study [Salonen et al.] found aggressive dogs were more than three times more fearful than non-aggressive dogs.


This study showed a clear correlation between males and aggression. However, some previous studies have found no difference between the sexes, and one [Guy et al] found female dogs are more likely to have bitten a human than male dogs.


Older dogs in this study were more prone to aggression, but other studies have shown inconsistent results. Researchers have found the association with age may actually be due to painful conditions or eye diseases that limit vision.


Of the breeds studied (23 dog breeds or breed groups), the Rough Collie, Miniature Poodle (toy, miniature and medium), Spanish Water Dog, Lagotto Romagnolo, and Miniature Schnauzer were the most prone to aggression. The least aggressive breeds in the study were the Golden Retriever, Labrador Retriever and Lapponian Herder. By comparison to the Golden and Labrador Retrievers, the Lagotto Romagnolo, Chihuahua, German Shepherd Dog and Miniature Schnauzer were more likely to exhibit aggressive behaviour.

Previous studies [Col, R. et al] agree that the Labrador and Golden Retrievers are the least likely to exhibit aggressive behaviour. Other studies have identified the Minature Poodle and Miniature Schnauzer as most likely to be aggressive to strangers, while the Lagotto Romagnolo was shown to be more aggressive to their human family members.

One of the most commonly restricted breeds, the Staffordshire Bull Terrier, was not one of the most aggressive breeds in this study.


Small dogs (calculated by typical breed size) were identified as being more aggressive than larger dogs. A higher level of fearfulness due to their small stature may account for a higher number of incidents.

Interestingly, a recently-published study associated several problematic behaviours (including aggression) with genetic variants known to cause small body size [Zapata et al].

Experience Level of ‘Owner’

Pet parents who have had at least one dog before, had a lower probability of aggressive behaviour in their dog than new pet parents. It is thought that more experienced custodians are better at spotting problems early and are more likely to prioritize socialization.

Other Dogs in the Home

Single dog homes may experience more aggression. That might be a simple matter of daily interactions with one of their own kind, which helps to prevent frustration and boredom. It could also be due to an increase in ‘people pleaser’ behaviour and competition for ‘good dog’ rewards.

Preventing Aggression

These findings suggest a number of ways that aggression in dogs may be prevented:

  • Education, especially of first-time dog parents.
  • Careful selection of breeds most suitable for your lifestyle.
  • Training and behaviour modification.
  • Selective breeding to avoid an inherited tendency towards aggression or anxiety, as well as painful health conditions.
  • Regular visits to your veterinarian to avoid or control painful conditions or diseases.

Don’t jump to any conclusions! Recognizing or anticipating aggression and seeking professional advice from a reputable trainer and veterinarian, is the first step towards understanding and addressing aggression in your dog.

Sources & Citations:

Mikkola, S., Salonen, M., Puurunen, J. et al. Aggressive behaviour is affected by demographic, environmental and behavioural factors in purebred dogs. Sci Rep 11, 9433 (2021). 

Dinwoodie, I. R., Dwyer, B., Zottola, V., Gleason, D. & Dodman, N. H. Demographics and comorbidity of behavior problems in dogs. J. Vet. Behav. 32, 62–71 (2019).

Bennett, P. C. & Rohlf, V. I. Owner-companion dog interactions: Relationships between demographic variables, potentially problematic behaviours, training engagement and shared activities. Appl. Anim. Behav. Sci. 102, 65–84 (2007).

Guy, N. et al. Risk factors for dog bites to owners in a general veterinary caseload. Appl. Anim. Behav. Sci. 74, 29–42 (2001).

Epstein, M. E. et al. 2015 AAHA/AAFP pain management guidelines for dogs and cats. J. Feline Med. Surg. 17, 251–272 (2015).

Col, R., Day, C. & Phillips, C. J. C. An epidemiological analysis of dog behavior problems presented to an Australian behavior clinic, with associated risk factors. J. Vet. Behav. 15, 1–11 (2016).

Hsu, Y. & Sun, L. Factors associated with aggressive responses in pet dogs. Appl. Anim. Behav. Sci. 123, 108–123 (2010).

Tiira, K., Sulkama, S. & Lohi, H. Prevalence, comorbidity, and behavioral variation in canine anxiety. J. Vet. Behav. 16, 36–44 (2016).

Duffy, D. L., Hsu, Y. & Serpell, J. A. Breed differences in canine aggression. Appl. Anim. Behav. Sci. 114, 441–460 (2008).

Zapata, I., Lilly, M. L., Herron, M. E., Serpell, J. A. & Alvarez, C. E. Genetic testing of dogs predicts problem behaviors in clinical and nonclinical samples. bioRxiv. (2020).

Liinamo, A.-E. et al. Genetic variation in aggression-related traits in Golden Retriever dogs. Appl. Anim. Behav. Sci. 104, 95–106 (2007).

MacLean, E. L., Snyder-Mackler, N., VonHoldt, B. M. & Serpell, J. A. Highly heritable and functionally relevant breed differences in dog behaviour. Proc. R. Soc. B Biol. Sci. 286, 20190716 (2019).

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