We investigated the demographic and environmental factors associated with two subtraits of canine social fearfulness, fear of dogs and fear of strangers, in a large behavioural survey data of 6,000 dogs using logistic regression. Social fearfulness was associated with several factors, which were almost identical in both subtraits. To sum up, fearful dogs were less socialised during puppyhood, small in body size, females and neutered, and participated less frequently in training and other activities. We also found a novel association between the living environment of the dog and social fearfulness, as dogs living in a more urban environment were more likely afraid of dogs and strangers. Moreover, we identified significant behavioural differences between dog breeds. These results reveal a comprehensive set of demographic and environmental factors associated with social fearfulness, but also highlight the role of genetic predisposition.

The level of socialisation during puppyhood (between seven weeks and four months of age) had the strongest association with both fear of dogs and fear of strangers. Fearful dogs had experienced less socialisation events in the age of 7–16 weeks than dogs showing no fear. Many mammals, including dogs, have a sensitive period for socialisation in the early postnatal life, during which the nervous system is immature and receptive for novel external stimuli34,35. Experiences and events taking place especially during 3–14 weeks of age can significantly affect dog’s behaviour throughout life29,30,35. In Finland, puppies are usually weaned and adopted to their new homes at the age of 7–8 weeks. This life change takes place during the sensitive period for socialisation, making the first weeks in the puppy’s new home crucial for the socialisation process.

Dogs weaned later than eight weeks of age were more likely to show fear of strangers than dogs weaned at a normal 7–8 weeks of age. This result might indicate that dogs weaned later encounter less socialisation experiences during the sensitive period than puppies moving to their new homes earlier. The breeder might not be able to provide an adequate amount of different kind of socialisation experiences when compared to the puppy’s new family. However, the association of inadequate socialisation and late weaning age might also reflect fearfulness already present at puppyhood. A fearful puppy might have to wait longer before it is adopted, and if it shows fear in the new home, it may not often meet unfamiliar people. Nevertheless, our results are consistent with earlier research, as it has been shown that early socialisation is necessary for normal social behaviour22,29,35 and that puppies weaned before the age of 12 weeks are bolder than puppies weaned later33. Therefore, development of social fearfulness may strongly depend on the diversity, amount, and proper timing of socialisation experiences.

We identified breed differences in fear of dogs and strangers. Spanish Water Dog and Shetland Sheepdog had a high probability of fear of dogs and strangers, whereas Wheaten Terrier had a low probability of both subtraits. Interestingly, the odds of showing fear greatly differed between the most and least fearful breeds, suggesting that some breeds might be more susceptible to fear than others. Many breed differences were similar in both fear of dogs and strangers, which could indicate comorbidity between these social fearfulness subtraits. However, some breeds only showed fear of dogs or strangers but not both. For example, Chihuahua and Border Collie rated high in fear of dogs but not in fear of strangers, whereas Miniature Schnauzer rated high in fear of strangers but not in fear of dogs.

Previous research has identified certain breeds that are more fearful than others36,37,38. These more fearful breeds include Chihuahua, Jack Russell Terrier, Lagotto Romagnolo, and Shetland Sheepdog. In contrast, German Shepherd Dog, Golden Retriever, Labrador Retriever, and Staff. Bull Terrier have been identified as less fearful breeds. We contrasted these fearful and non-fearful breeds and indeed discovered a difference in the probability of fear of dogs and strangers. However, more precise comparisons with previous research are difficult as the breed composition of study cohorts has been highly variable and moreover, instead of individual breeds, breed groups are often used to overcome small sample sizes in the statistical analyses. As a result, comparisons between findings of different studies might not be very meaningful.

We discovered that small dogs were more likely to show fear of dogs and strangers than large dogs. This result agrees with previous studies showing that fear of dogs and strangers decreases as the height of the dogs increases39, and that larger dogs are bolder in general38,40,41. Small sized dogs may feel more threatened by people and larger dogs due to the larger relative size difference and hence be more fearful. In addition, small dogs may not be trained and socialised enough42, as their small size makes them easier to handle even when they behave badly or unpredictably. Thus, undesirable behaviours may be more tolerated in small dogs than in larger conspecifics. For the same reason, behaviour may not be an important factor when making breeding plans, and thus, unwanted behaviours may accumulate. Another explanation is that body size could be genetically associated with reactivity and stress tolerance in dogs. However, as the most fearful breeds also include small sized breeds, despite having size as an explanatory variable in the models, the breed itself may be more important factor than the body size. This result emphasises the role of genetic predisposition in the development of behaviour and behavioural problems.

Interestingly, the living environment of the dog was associated with social fearfulness, as dogs living in an urban environment were more likely afraid of dogs and strangers than dogs living in more natural and agricultural areas. The relationship between behaviour and the living environment has not been studied in dogs before, but studies in humans have reported higher rates of mental disorders in urban areas when compared to rural environments43,44,45. However, the results have been somewhat inconsistent depending on, for example, the geographical location studied. In addition, the causality and mechanisms behind these associations are still mainly uncovered but studies have suggested several factors, such as diet, environmental toxins, stress, and social isolation43,46. As dogs share the environment with us, similar environmental factors could mediate this association in both species. In addition, urban areas, such as cities, may be very hectic and stressful environments to live as they are full of different stimuli, such as sudden and loud noises, potentially predisposing dogs to fear-related and other behavioural problems. On the other hand, dogs living in rural environments may meet other dogs and strangers less frequently due to the lower population density in rural areas. Nevertheless, in the lack of previous literature, no further conclusions can be made about the observed association between the urban environment and higher social fearfulness in dogs.

We found that dogs engaging in activities and training less frequently were more likely to show fear. In both subtraits, dogs participating only seldom in activities and training had a significantly higher likelihood to be fearful when compared to dogs participating in activities and training sometimes or weekly. Additionally, fear of conspecifics was associated with daily exercise. Dogs exercising less than two hours a day were more likely fearful than dogs getting more than three hours of exercise. Interestingly, lower levels of exercise have been previously associated with noise sensitivity and fear of strangers22,47. The observed associations may be explained by multiple different phenomena. Activities and exercise can fulfil dogs’ species-specific needs, acting as a way to reduce stress48. Therefore, dogs participating in activities more often may cope better in challenging situations. Previous research has demonstrated that both social and environmental enrichment together with exercise improves the wellbeing of dogs in kennels49,50. Moreover, dogs that engage more in activities and exercise may also habituate to the fearful stimuli. Additionally, dogs that are trained often likely interact more with their owners, possibly strengthening the human-dog bond7,51. Thus, the dog may feel safer in the presence of its owner and show less fear. On the other hand, owners may not be willing to train and exercise fearful dogs, as they may be difficult to handle and behave unpredictably, causing inconvenience and stress to the owner. Therefore, more research is needed to better understand the relationship between activities and social fearfulness.

Consistent sex differences in fearfulness were observed both in our dataset and in previous studies22,33,36,37,52,53. Females tend to be generally more fearful than males, and we observed the same trend in both fear of dogs and fear of strangers. In addition, neutered dogs were more likely afraid of dogs and strangers than intact dogs. Similar results have also been obtained earlier22,52,53. Moreover, we detected a significant interaction between sex and sterilisation in fear of dogs, as intact males were less fearful than intact females, but neutered males and females did not differ from each other. Interestingly, no interaction between sex and sterilisation was observed in fear of strangers. In some previous studies, neutering has been demonstrated as a risk factor for several problematic behaviours, potentially because of the hormonal changes caused by gonadectomy54,55. However, sometimes veterinarians may suggest neutering as a treatment for behavioural problems. In addition, dogs with undesirable behaviours are less likely used for breeding purposes, and thus they may be more likely neutered. Therefore, the causality of the relationship between neutering and social fearfulness remains elusive in our study.

Older dogs showed less fear of dogs, as the likelihood of fearfulness decreased after six years of age. A similar trend was also observed in fear of strangers, but the association was not significant. These results are supported by our previous studies: Tiira and Lohi (2015)22 discovered that younger dogs were generally more fearful, and Salonen et al.17 found that dogs 4–8 years old were most fearful of both dogs and strangers. However, opposite results have also been demonstrated33,52. The decline in fearfulness with age suggests that dogs may habituate to fearful stimuli and develop strategies to cope in these situations. Moreover, owners of fearful dogs may also adapt their actions, and learn to avoid situations in which the dog feels uncomfortable and shows fear.

In this survey study, we demonstrate that socialisation during puppyhood is strongly associated with social fearfulness in dogs, consistent with previous research. We have also replicated other findings from previous studies, as we show that fearful dogs are more often small, females and neutered, and participate less often in training and exercising. In addition, we identified several breed differences, suggesting that some breeds may be more vulnerable to develop social fear-related problems than others. Moreover, we report a novel association between the living environment of the dog and social fearfulness that requires further research. Most of the identified risk factors were common for both fear of dogs and fear of strangers, but we also identified some subtrait-specific risks, such as the association of daily exercise and fear of dogs, and the association of weaning age and fear of strangers. Our results indicate that social fearfulness in dogs is affected by multiple demographic and environmental factors and suggest that careful consideration and management of these factors could improve the wellbeing of pet dogs.