Dog Bite Levels Explained: Severity, First Aid and What to Do Next

By Dr Duncan Houston.

A dog bite can range from a warning snap that causes no injury to a life-threatening attack. Understanding the physical severity of a bite can help guide immediate safety decisions, medical care and behavioural assessment.

The commonly used Dunbar Bite Scale classifies incidents from Level 1 to Level 6. A modified version developed by veterinary behaviourist Dr Sophia Yin separates Level 3 into Level 3A and Level 3B.

The scale describes the injury caused. It does not diagnose why the dog bit, prove intent or reliably predict future behaviour on its own.

Quick Answer

If a dog has bitten or attempted to bite:

Separate everyone safely without grabbing the dog’s collar or placing your hands between fighting animals.
Control serious bleeding with firm pressure.
Wash human wounds thoroughly with soap and running water.
Seek appropriate medical or veterinary care.
Prevent further access to the victim or trigger.
Arrange a veterinary examination for the dog.
Contact a qualified behaviour professional.
Check local bite-reporting and rabies requirements.

Never punish the dog after the event. Punishment may increase fear, suppress warning signals and make future incidents less predictable.

What Is the Dunbar Dog Bite Scale?

The Dunbar Bite Scale was developed by veterinarian and animal behaviourist Dr Ian Dunbar to classify the physical severity of dog bites.

Its six levels range from threatening behaviour without skin contact to a fatal attack. The official Dunbar Bite Scale focuses on observable injuries rather than assumptions about motivation.

Dr Sophia Yin later popularised a modification separating Level 3 incidents into:

Level 3A: One bite producing shallow punctures
Level 3B: Multiple bites producing shallow punctures

This distinction helps identify incidents involving repeated biting, but it is still only one part of a complete risk assessment.

Level 1: Aggressive Behaviour Without Tooth Contact

The dog may:

Growl
Bark
Lunge
Snarl
Snap towards a person
Air snap without making contact

No teeth touch the person’s skin.

An air snap is not necessarily a “missed bite”. Dogs often have excellent control over their mouths, and the snap may be a deliberate warning intended to increase distance.

What it may mean

The dog could be experiencing:

Fear
Pain
Frustration
Resource guarding
Handling sensitivity
Territorial behaviour
Overstimulation
Conflict or uncertainty

What to do

Stop the interaction.
Give the dog space.
Identify what happened immediately beforehand.
Do not punish the warning.
Prevent the situation from being repeated.
Arrange professional help if the behaviour is new, frequent or escalating.

A Level 1 incident causes no physical injury, but it still provides important information about the dog’s emotional state.

Level 2: Tooth Contact Without Skin Puncture

The dog’s teeth touch the skin but do not create a puncture wound.

There may be:

Redness
Superficial scratches
Minor bruising
Small nicks caused by tooth movement

This indicates that the dog made contact while retaining some bite inhibition.

What to do

End the interaction calmly.
Check the skin carefully.
Wash any superficial injury.
Prevent another incident.
Arrange a veterinary examination if the behaviour was sudden or unexpected.
Begin a formal behaviour and safety assessment.

Although the skin was not punctured, Level 2 should not be dismissed as harmless.

Level 3A: One Bite with Shallow Punctures

The dog delivers one bite that produces one or more punctures. No puncture is deeper than approximately half the visible length of the dog’s canine tooth.

There may also be shallow scratches or lacerations caused as the victim or dog moves away.

What to do

Provide immediate wound care.
Seek medical advice when human skin has been punctured.
Obtain veterinary care if another animal was bitten.
Prevent all further exposure to the original situation.
Arrange veterinary and behavioural assessment.
Check local reporting requirements.

A Level 3A bite is significant. However, it does not automatically mean the dog is destined to bite more severely in the future.

Level 3B: Multiple Bites with Shallow Punctures

The dog bites more than once, producing multiple shallow puncture wounds.

Repeated biting may indicate that:

Arousal remained high
The dog struggled to disengage
The trigger remained present
The incident continued without a safe exit
Another person or animal continued moving or fighting

What to do

Level 3B incidents require prompt professional involvement.

Use physical barriers and controlled separation.
Restrict access to children and vulnerable people.
Seek medical or veterinary care for the victim.
Arrange a medical examination for the dog.
Contact a veterinary behaviourist or suitably qualified behaviour professional.
Begin muzzle training and environmental management when professionally advised.

Do not attempt to recreate the incident to “see whether it happens again”.

Level 4: One Bite with Deep Puncture or Tearing

A Level 4 incident involves one bite with:

One or more punctures deeper than half the length of the canine tooth
Significant bruising
Crushing injury
Lacerations in more than one direction
Evidence that the dog clamped down, held or shook

This is a severe bite with substantial potential for injury.

What to do

Treat the incident as an emergency.
Obtain immediate medical or veterinary care for the victim.
Securely separate the dog.
Prevent contact with children, visitors and other animals.
Arrange an urgent veterinary examination.
Seek assessment from a veterinary behaviourist.
Review legal and reporting obligations.
Implement a written safety and management plan.

Do not casually rehome a dog after a serious bite. Rehoming may transfer an undisclosed risk to another household and may be unsafe or unlawful.

Level 5: Multiple Level 4 Bites or Repeated Severe Attacks

The original Dunbar scale describes Level 5 as:

A multiple-bite incident involving at least two Level 4 bites, or
Multiple attack incidents involving at least one Level 4 bite

These cases represent an exceptionally serious safety concern.

What to do

Immediate measures may include:

Complete separation from potential victims
Secure barriers and locked access points
Basket muzzle conditioning
Direct adult supervision
Veterinary investigation for pain or disease
Veterinary behaviourist assessment
Contact with local authorities or insurers where required
An honest assessment of whether safe lifelong management is realistic

Decisions about management, placement or behavioural euthanasia must be made individually with veterinary, behavioural and legal input. Bite level alone should not be the only factor, but the severity cannot be minimised.

Level 6: Fatal Attack

A Level 6 incident is one in which the victim dies.

This is the most severe category and requires immediate involvement from:

Emergency medical services
Police or animal control
Public health authorities
Veterinary professionals
Other relevant local authorities

Level 6 describes the outcome of the incident. It does not attempt to explain the dog’s motivation.

The Bite Level Does Not Tell the Whole Story

Two incidents producing similar wounds may carry very different future risks. A complete assessment considers:

What happened before the bite
Whether the trigger was identifiable
Whether the dog attempted to escape
Warning signals shown beforehand
The dog’s ability to disengage
The number and depth of bites
Previous bite or aggression history
Whether incidents are escalating
The age and vulnerability of potential victims
Access to children or dependent adults
The dog’s size, speed and physical ability
Pain, illness or neurological disease
The household’s ability to maintain safety measures

Risk exists within the interaction between the dog, people, other animals and environment. It should not be assessed from breed or wound severity alone. The American Veterinary Medical Association also advises against treating breed as a reliable predictor of aggression.

Why Do Dogs Bite?

Dogs may bite because of:

Fear or anxiety
Pain or illness
Resource guarding
Handling or restraint
Territorial behaviour
Maternal behaviour
Frustration
Conflict with another animal
Startling while asleep
Redirected aggression
Predatory behaviour
Learned associations
Neurological disease
Cognitive decline

Saying that every dog bites because earlier warnings were ignored oversimplifies the issue. Some warnings are extremely subtle, while others may not be visible before a rapidly triggered incident.

A veterinarian should investigate any sudden, uncharacteristic or escalating aggression.

What to Do Immediately After a Human Is Bitten

1. Create safety

Secure the dog behind a closed door, barrier or other reliable form of separation. Do not hit, corner or physically confront the dog.

If an attack is continuing and cannot be stopped safely, contact emergency services or local animal control.

2. Control bleeding

Apply firm pressure using clean cloth or gauze. Call emergency services if bleeding is severe or does not stop.

3. Clean the wound

Wash broken skin thoroughly with soap and running water. Public health guidance recommends prolonged washing, particularly where rabies exposure may be possible. World Health Organization

4. Obtain medical advice

Seek prompt medical care for:

Any deep puncture
Crushing or tearing injuries
Bites to the face, hands, feet, genitals or near a joint
Uncontrolled bleeding
Numbness or loss of movement
Bites involving children, older adults or immunocompromised people
Increasing pain, swelling, redness or discharge
An unknown dog
An unvaccinated dog
Any possible rabies exposure

A healthcare professional may assess the need for antibiotics, tetanus vaccination, rabies prevention or further wound treatment.

Rabies requirements depend on the country, location, animal and vaccination history. The CDC advises urgent medical assessment after a possible rabies exposure.

What to Do When Another Animal Is Bitten

Dog bite wounds can look small at the surface while hiding:

Deep tissue damage
Crushing injuries
Internal bleeding
Chest or abdominal penetration
Joint involvement
Infection
Damage beneath thick fur

Arrange veterinary care, particularly if there is a puncture, swelling, pain, breathing difficulty, limping, weakness or any bite involving the chest, abdomen, face, eye or neck.

Do not give human pain medication unless instructed by a veterinarian.

Reporting and Documentation

Bite-reporting rules vary between countries, states and councils. A bite is not automatically reportable everywhere simply because it meets a particular level.

After an incident:

Record the date, time and location.
Photograph injuries when appropriate.
Write down what occurred before, during and after the bite.
Record the dog’s vaccination details.
Obtain contact details for everyone involved.
Keep medical and veterinary records.
Contact local authorities or public health services for reporting guidance.

Do not alter or destroy records. Accurate documentation supports medical care, behavioural assessment and legal decision-making.

The Dog Also Needs a Veterinary Examination

Pain and disease can reduce a dog’s tolerance and change behaviour.

Your veterinarian may investigate:

Dental pain
Ear disease
Arthritis
Spinal pain
Skin disease
Gastrointestinal discomfort
Vision or hearing loss
Hormonal or metabolic disease
Neurological disorders
Medication effects
Cognitive dysfunction

Treating an underlying condition may reduce risk, but medical treatment does not replace a safety and behaviour plan.

Building a Safety Plan

A personalised plan may include:

Secure doors, gates and barriers
Separation during visitors or meals
Preventing access to known triggers
Direct supervision around children
Separate feeding areas for pets
Avoiding forced handling
Basket muzzle training
Lead and harness management
Teaching recall, targeting and mat behaviours
Reward-based behaviour modification
Medication when prescribed
Regular professional reassessment

A basket muzzle can reduce injury risk, but it does not make unsafe situations appropriate. It must be fitted correctly and introduced gradually with positive reinforcement.

What Not to Do After a Bite

Avoid:

Hitting, shouting at or physically confronting the dog
Punishing growling or warning signals
Using shock, prong or choke collars
Forcing the dog back into the triggering situation
Allowing children to “make friends” with the dog
Testing the dog with another person or animal
Assuming obedience training alone will solve aggression
Hiding the dog’s bite history
Rehoming without complete disclosure and professional guidance
Relying only on social media advice

Punishment may temporarily suppress behaviour without changing the underlying fear, pain or motivation.

Preventing Future Dog Bites

Learn early body-language signals

Watch for:

Turning the head away
Lip licking
Yawning
Freezing
Crouching
Showing the whites of the eyes
Moving away
Stiffening
Growling
Raising the lips
Hard staring

Respect growling

A growl is valuable information. Punishing it may remove the warning while leaving the underlying discomfort unchanged.

Supervise children properly

Direct supervision means an attentive adult is close enough to intervene. If that is not possible, use complete physical separation.

Children should never:

Climb on a dog
Hug tightly
disturb a sleeping dog
Take food or toys
Corner a dog
Place their face near the dog’s face

Use reward-based training

Teach practical safety behaviours such as:

Recall
Hand targeting
Going to a mat
Dropping objects
Moving behind a barrier
Voluntary muzzle wearing

Frequently Asked Questions

Does an air snap mean my dog tried to bite and missed?

Not necessarily. An air snap may be a controlled warning. It should still be taken seriously because the dog is communicating discomfort or a need for distance.

Is every skin-breaking bite automatically Level 3?

A shallow puncture may fit Level 3, but wound depth and the number of separate bites matter. Medical professionals should assess the injury regardless of its classification.

Does a Level 3 bite mean the dog will eventually deliver a Level 4 bite?

No. Bite level alone cannot predict future behaviour. Risk depends on the trigger, history, environment, medical health, management and many other factors.

Is one Level 4 bite worse than several Level 3 bites?

Both require serious assessment. Wound depth is important, but repeated biting, predictability, victim vulnerability and the household’s ability to prevent recurrence also affect risk.

Should a dog be euthanised after biting?

There is no responsible universal answer. Decisions should consider severity, frequency, predictability, medical findings, victim vulnerability, quality of life and whether reliable management is realistically possible.

Can a dog with a bite history be rehomed?

Sometimes, but rehoming may simply transfer the risk. Full disclosure, legal guidance and professional assessment are essential. Some dogs cannot be safely or ethically rehomed.

Who should assess a biting dog?

Begin with your veterinarian. Depending on the case, seek a board-certified veterinary behaviourist or another appropriately qualified, reward-based behaviour professional experienced in aggression cases.

Final Thoughts from Dr Duncan Houston

A bite scale gives us a shared way to describe physical injury, but it is not a verdict on the dog.

Every incident deserves careful consideration of the victim, the dog, the trigger and the environment. Immediate safety comes first, followed by medical care, veterinary investigation and qualified behavioural support.

Early intervention at Levels 1 and 2 may prevent serious injuries. Once punctures or repeated bites occur, professional assessment should not be delayed.

Get Dog Bite and Behaviour Support with ASK A VET™

If your dog has growled, snapped or bitten, knowing what to do next can feel overwhelming. ASK A VET™ can help you organise the information and take safer next steps.

Through the ASK A VET™ app, you can:

Discuss sudden or concerning behaviour with a veterinary professional
Share videos of body language when it is safe to record
Record incidents, triggers and warning signs
Track medical and behavioural changes
Prepare a practical household safety plan
Understand when an examination or specialist referral is needed

ASK A VET™ does not replace emergency services, wound treatment, public health advice or local reporting requirements.

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About the author

Dr Duncan Houston

Veterinarian · Founder of ASK A VET

Every ASK A VET article is written and reviewed by qualified veterinarians.

About Dr. Duncan →drduncanthevet

Dog Bite Levels Explained: Severity, First Aid and What to Do Next