What Makes a Dog “Dangerous”?
The debate about “dangerous dogs” cannot move forward without first clarifying the meaning of “dangerous.” A thing, activity, dog, or person should be considered “dangerous” if it or he presents an unacceptably high risk of serious injury, even before causing harm.
This definition emphasizes risk. Cars, plastic bags, and electrical cords are dangerous not because of their individual history of crashes, suffocations, or electrocutions, but because of their potential for harm. When applying this concept to dogs, the issue is not whether a particular dog will ever bite, but whether it presents too great a risk of serious injury—based not on its own past, but on what others of its class have done.
The definition also uses the term serious injury. The bites of very small dogs, or herding dogs that use their mouths to seize and guide rather than crush and rip, generally do not present the same risk of serious injury as the bites of dogs bred specifically to kill animals. When “dangerous” is defined in this way, many believe it accurately describes the latter group.
Legal Meaning of “Dangerous Dog”
A dog can be legally classified as “dangerous” or “vicious” based upon its actions, its breed, or the conduct of its owner, either before or after an official hearing, pursuant to the law of the jurisdiction where the dog is present. (Blacks Law Dictionary 589 (10th ed. 2014), following the definition previously set forth in this article on dogbitelaw.com.)
Once classified, a “dangerous” or “vicious” dog is subject to strict rules of confinement or care, and may even be euthanized. Its owner may be fined, jailed, and ordered to comply with conditions affecting the keeping of animals.
These statutes are commonly known as “dangerous dog laws.” They usually appear in municipal or county codes, but often form part of a state code as well. Case law can also become part of the dangerous dog law, as can local regulations such as those issued by a city’s animal control department—even if technically not part of the statute itself.
Distinction Between “Dangerous” and “Vicious”
The law often distinguishes between the two terms.
Dangerous usually refers to the risk of harm from any action of the dog, even if benign. This includes biting, jumping, knocking into people, grabbing, swiping with paws, or overly friendly behavior such as leaping on strangers. For example, a dog that habitually runs toward and jumps on people could be deemed dangerous because of the risk of harm to an elderly pedestrian.
Attorney Kenneth Phillips has also argued that a dog’s propensity to chase or fight with other domestic animals should be considered dangerous to people, because such incidents often lead to serious human injuries. (See, A Propensity to Attack Other Dogs Means a Dog Is Dangerous to People.)
Vicious refers to a dog that has demonstrated, by its actions, an intention, habit, or tendency to cause harm to people. For example, a dog that repeatedly jumps on people might be classified as dangerous, but not vicious.
Basis for Classification
The criteria for declaring a dog “dangerous” or “vicious” vary across jurisdictions. All aim to reduce unacceptable risks, but the focus can differ:
- Some jurisdictions classify a dog as dangerous if it threatens a person, even without causing injury.
- Others base the classification on repeated violations of animal control rules by the owner. In effect, it is the owner who is deemed dangerous, and the dog is regulated because of the risk posed in that person’s hands.
- Several nations and U.S. cities classify entire breeds as “dangerous,” regardless of any individual dog’s temperament or behavior.
For a summary of the statutory definitions of “dangerous” and “vicious” dog from all 50 U.S. states and the District of Columbia, see “Dangerous” and “Vicious” – A Comparative Analysis of Statutory Definitions in the USA by Attorney Kenneth M. Phillips (Aug. 12, 2025).
Legislative Findings
Many statutes contain findings that explain the need for dangerous dog laws. For example, the Colorado State Legislature enacted this finding (codified in Colorado Revised Statutes):
18-9-204.5. Unlawful ownership of dangerous dog.
(1) The general assembly hereby finds, determines, and declares that:
(a) Dangerous dogs are a serious and widespread threat to the safety and welfare of citizens throughout the state because of the number and serious nature of attacks by such dogs; and
(b) The regulation and control of dangerous dogs is a matter of statewide concern.
Similarly, the California State Legislature studied dog bites and passed this finding (codified as section 31601 of the Food & Agriculture Code):
31601. The Legislature finds and declares all of the following:
(a) Potentially dangerous and vicious dogs have become a serious and widespread threat to the safety and welfare of citizens of this state. In recent years, they have assaulted without provocation and seriously injured numerous individuals, particularly children, and have killed numerous dogs. Many of these attacks have occurred in public places.
(b) The number and severity of these attacks are attributable to the failure of owners to register, confine, and properly control vicious and potentially dangerous dogs.
(c) The necessity for the regulation and control of vicious and potentially dangerous dogs is a statewide problem, requiring statewide regulation, and existing laws are inadequate to deal with the threat to public health and safety posed by vicious and potentially dangerous dogs.
The bill that amended section 399 of the California Penal Code (Bill No. AB 1709) contained this urgency finding:
SEC. 3. This act is an urgency statute necessary for the immediate preservation of the public peace, health, or safety within the meaning of Article IV of the Constitution and shall go into immediate effect…. In order to protect the public from the rising incidents of dog maulings across the state it is necessary for this act to take effect immediately as an urgency statute.
Los Angeles County has a similar statement in its code:
10.37.010 Purpose of this chapter. Within the county of Los Angeles there are potentially dangerous and vicious dogs that have become a serious and widespread threat to the safety and welfare of the citizens of the county which should be abated.
Conclusion
Although we may feel we know a dangerous dog when we see one, the reality is more complex. Dangerousness is a political and controversial issue, and the laws that address it are often confusing and contradictory.