OVERVIEW: What veterinary research reveals about pain, biting, and the danger of mistaking illness for disobedience. Aggression in dogs is not always a behavioral problem; sometimes it is a response to physical pain or illness. Drawing on veterinary research and my firsthand cases involving cancer, arthritis, spinal disorders, dental infections, pancreatitis, and severe allergies, this article examines how medical conditions can contribute to biting and attacks, why these causes are often overlooked, and how appropriate veterinary care can sometimes resolve aggression without behavioral modification.

By Sam Basso | Professional Dog Trainer

More than twenty-five years ago, a woman called me about her one-year-old black Labrador Retriever. Until then, she had considered him an ordinary young Lab. One day she went into the yard to bring him inside, but he remained lying on the ground when she called. She approached, took hold of his collar, and tried to pull him up. He attacked her.

Shaken, she spoke with a neighbor who described himself as a German Shepherd trainer. His advice was that if his own dog had done such a thing, he would have “beat the hell” out of him. Fortunately, she sought another opinion.

When I evaluated the Labrador, I was troubled by the sequence of events. A young dog without an apparent history of aggression had refused to get up, and the attack occurred when his owner tried to move him. I could not explain the incident, but I was not satisfied that we were looking at a behavioral disturbance or a conventional training problem. I suggested a veterinary examination. The veterinarian found cancer.

The cancer had spread throughout the dog’s body, and the veterinarian confirmed that it was painful. That dog was seriously ill, and that a proposed beating would have subjected him to further suffering without first asking why he had remained on the ground. That case has influenced my work ever since.

A couple of years ago, I worked with an Australian Cattle Dog whose aggressive behavior did not improve as expected with behavioral modification. At the beginning of our work, I recommended a veterinary examination to investigate possible medical contributors, but nothing significant was identified at the time. Earlier this year, he died from cancer. Looking back, I wonder whether the disease had already been developing when I first evaluated him, perhaps affecting his behavior before there were recognizable clinical signs. Neither the veterinarian nor I had evidence of cancer at the time, and I cannot establish that it caused his aggression. Nevertheless, knowing what eventually happened has changed how I interpret that case. I now suspect that an undetected medical condition may have been a major contributor to the behavioral problems we were trying to address.

The medical question behind a bite

When an owner calls about aggression, the event itself usually dominates the conversation: a bite, an attack on another dog, or an incident in which a family member was injured. Safety must come first. Yet the sequence preceding the attack may tell us more than the attack alone. Who approached? Was the dog resting? Was someone trying to lift or restrain him? Had his movement, appetite, sleep, or willingness to be handled changed recently?

Behavior is not reducible to the final action we happen to witness. A bite occurs within a larger process shaped by physical condition, previous experience, environment, and what the dog is capable of doing at that moment. Pain is one possible contributor. It is not a universal explanation, but neither is it an exotic one.

A particularly relevant veterinary paper appeared in 2012. Tomás Camps and colleagues described twelve clinical cases of dogs with pain-related aggression; eight had hip dysplasia. The authors reported differences between dogs with previous aggression histories and those whose aggression appeared in connection with pain, including handling-related responses [1]. Twelve selected cases cannot tell us how often pain contributes to biting across the dog population. They can, however, establish that the combination of painful disease and aggressive handling responses is a genuine clinical concern.

The numerical results make the Camps study more revealing than a general assertion that pain and aggression are related. In the twelve-case series, dogs without an earlier aggression history were more likely to show aggression during manipulation (P = 0.0143) and to be described as impulsive (P = 0.0209). The comparison for defensive body posture approached, but did not reach, the conventional 0.05 threshold (P = 0.0533). These figures describe differences within a small, selected clinical group. They are not probabilities that an arbitrary dog with hip dysplasia will bite, and the sample was too small to establish breed-specific risk. The conditions included eight cases of hip dysplasia, two of chronic otitis, one skin injury, and one elbow osteoarthritis [1].

The authors also separated dogs whose aggression predated the painful condition from those whose aggression emerged afterward. That distinction matters because an animal with an established history of aggressive encounters may respond differently from one that first attacks during painful handling. The paper did not supply a controlled, long-term estimate of how many dogs stopped biting after treatment. Nor could it reconstruct the subjective experience of each dog at the instant of an attack. It offers clinical characterization, not a cure rate.

The Labrador’s refusal to rise remains the detail I find most instructive. It could have been interpreted as stubbornness. In a different dog it might have been simple inattention. But once an attack followed physical prompting, it became important to investigate what moving might have meant to that particular animal. A trainer can recognize the need for that investigation without claiming to know the medical answer.

What owners may not see

Pain does not always announce itself through crying or an obvious limp. Dogs may continue eating, greeting people, and taking part in familiar routines while experiencing discomfort. Gradual changes are especially easy to overlook: a dog takes longer to rise, hesitates before jumping into the car, stops enjoying rough play, or becomes less tolerant of being bumped. The 2022 American Animal Hospital Association pain-management guidelines emphasize the importance of veterinary examination alongside observations of posture, movement, function, and behavior reported by owners [8].

Osteoarthritis is a useful example. In a large United Kingdom primary-care study, researchers examined veterinary records from more than 455,000 dogs and found that 2.5 percent had a recorded osteoarthritis diagnosis during the study year [6]. That figure reflects documented diagnoses in a defined population, not the total prevalence of undetected pain. A separate study used owner observations and veterinary examinations to identify osteoarthritis and then monitored physical function during veterinarian-directed care [7]. Improvements in mobility are meaningful, but these studies did not establish that medication prevents biting.

The scale of the osteoarthritis research is valuable, but it must be read correctly. Anderson and colleagues analyzed a large primary-care population rather than a sample selected for aggression. The 2.5 percent figure was a one-year prevalence of recorded osteoarthritis diagnoses, not a lifetime probability and not the true prevalence of every painful joint in Britain. Their analyses found differences by age, body weight, and breed. This gives veterinarians epidemiological context when assessing mobility complaints; it does not turn any breed into an aggression category [6].

Wright and colleagues approached osteoarthritis from another direction: could an owner questionnaire help identify affected dogs, and could functional mobility measurements track response to care? Their screening process involved 500 dogs, with osteoarthritis confirmed in 188; a treatment-monitoring subset included 133 dogs. The outcomes concerned pain and physical function, including mobility tasks—not biting or attacks. For this article, that is supporting evidence about an often-overlooked source of discomfort, not direct evidence of an anti-aggression effect [7].

I evaluated a male Great Dane whose owner was concerned about his reactions to other dogs running nearby. To observe the behavior, I accompanied the owner to the fence line of an off-leash dog park. Sure enough, when dogs ran close to him, the hair along his back stood up, a response known as piloerection. The Great Dane had hip dysplasia, and I suspected that the approaching dogs made him feel physically vulnerable. A dog with painful or unstable hips may have good reason to be concerned about being bumped, knocked off balance, or forced into a sudden movement. Piloerection alone does not establish fear or aggression, but the circumstances suggested that his response was not necessarily a conventional dog-to-dog behavioral problem. I believed his orthopedic condition was an important part of the explanation. Treating him as simply intolerant of other dogs would have overlooked the possibility that he was trying to protect himself from painful contact.

Spinal disease presents another problem. Disorders affecting the neck or back can make movements such as being lifted, turning, or having a collar pulled uncomfortable. Intervertebral disc disease is well documented in breeds including Dachshunds and French Bulldogs, although disease risk is not an aggression prediction [12]. A dog may also have neurological deficits or abnormal sensation rather than pain alone. Such distinctions belong to veterinary examination, not guesswork by a trainer.

The neck deserves special attention in the interpretation of a collar-related incident, although a collar reaction cannot diagnose a cervical disorder. Intervertebral disc disease, degenerative changes, and other neurological or musculoskeletal conditions can produce different combinations of pain, weakness, altered movement, or abnormal sensation. A dog with neurologic impairment may not be refusing to move in the ordinary sense at all. Veterinary assessment must distinguish pain from weakness and from other causes of altered movement. Clinical research comparing disc extrusions across Dachshunds, French Bulldogs, and English Cocker Spaniels illustrates why breed history can inform the medical differential without determining an individual diagnosis [12].

Another case involved a Boerboel, an exceptionally large dog with narrowing of the spinal canal in his neck and compression affecting the spinal nerves. He had lashed out when people petted him around his head and neck, and he strongly resisted having a collar and leash put on. The veterinarian advised against using a collar or leash because of his cervical condition. In this case, the relationship between physical contact and pain was particularly important: what appeared to be aggression toward people could also be understood as an attempt to prevent handling that hurt him. His extraordinary size complicated matters further. Surgery, if medically feasible, would have presented substantial questions about risk, expense, and recovery. I also wondered whether breeding for excessive size had contributed to his physical problems. That possibility cannot be established from one dog, but it raises a legitimate concern about breeding practices that prioritize extreme physical characteristics without sufficient attention to structural health and long-term welfare.

Other painful conditions are less visible. Fractured or infected teeth can make handling around the mouth unpleasant even when the dog continues to eat. Pancreatitis can involve significant abdominal discomfort, sometimes accompanied by vomiting, poor appetite, or weakness [11]. In my own work, owners have described reduced aggression after veterinarians addressed dental infections, pancreatitis, orthopedic problems, and spinal conditions. These are field observations, not controlled demonstrations that each illness caused each attack. They matter because they show why a trainer should not restrict the investigation to obedience or learning history.

Oral disease deserves more than a passing mention because a dog may continue eating even while a tooth or the surrounding tissues hurt. Periodontal inflammation, fractured teeth, tooth-root disease, and oral tumors can all require veterinary attention. The 2019 American Animal Hospital Association dental guidelines describe periodontal disease as a common, frequently overlooked source of pain and infection [14]. An owner might notice reluctance to chew on one side, dropping food, bad breath, a changed interest in toys, or a new objection to the face being touched. None of these signs diagnoses dental disease, and a normal appetite does not rule it out. A dog that resists having its mouth opened, being groomed around the muzzle, or being physically guided by the head may be protecting a painful area rather than refusing to cooperate.

Years ago, when I was living in Bellevue, Washington, I worked with a small black dog on Mercer Island that had bitten numerous people. The dog was eventually found to have such severe dental infections that every tooth had to be extracted. By then, the disease was too advanced to save them. Following the surgery and recovery, the biting stopped. Some might argue that a toothless dog simply could no longer bite effectively, but that explanation misses an important distinction: a dog without teeth can still attempt to bite, even if the consequences are different. According to the outcome reported to me, this dog stopped making those attempts. I believe the relief of severe oral pain was the decisive change. Although we cannot prove that pain accounted for every earlier incident, the sequence strongly suggested that what had appeared to be a serious behavioral problem was closely associated with an equally serious medical condition.

The veterinary dental examination may reveal problems that a trainer cannot see, including disease below the gumline. An awake look at the mouth is not equivalent to a complete dental assessment, and a distressed or aggressive dog should not be forcibly examined by an owner. As with arthritis, the existence of a painful dental condition is established more securely than its precise contribution to a particular bite. Where owners report improvement after dental treatment, the strongest account records both the veterinarian’s findings and the circumstances in which handling became easier, rather than simply declaring the dog cured of aggression.

Pain from internal organs can be even more deceptive. The abdomen contains structures that can be inflamed, distended, obstructed, or otherwise diseased without producing an obvious limp or a visible injury. Gastrointestinal disease, urinary disorders, and some abdominal masses can be associated with discomfort; other organ diseases may cause weakness, nausea, altered activity, or neurological changes without necessarily causing pain. The relevant clinical question is not whether every organ disease produces aggression. It is whether the dog has an illness that changes how movement, pressure, handling, or ordinary social contact feels. That distinction requires a veterinary history and examination, and sometimes laboratory testing or imaging.

Pancreatitis provides a particularly vivid example of visceral pain. The pancreas is involved in digestion and blood-glucose regulation; inflammation can cause severe abdominal discomfort as well as vomiting, reduced appetite, weakness, and dehydration. Mild or chronic presentations may be much less obvious. A 2025 professional review in the Merck Veterinary Manual explains that canine pancreatitis is diagnosed by integrating clinical findings with pancreatic lipase testing and, when appropriate, imaging, rather than relying on one sign or test [15]. A dog may be reluctant to change position, tense its abdomen, or react when bumped, although those responses are not specific to pancreatitis. Veterinary care addresses the disease and its complications; it is not a behavioral experiment.

I worked with two adult Boxers that fought when the younger dog bumped into the older one. The older Boxer was subsequently found to have pancreatitis, which was very painful. That finding changed the interpretation of the fights. What looked at first like a conflict between two dogs also involved an animal with a serious source of abdominal pain, and accidental contact may have been especially unpleasant. I cannot say from the case history alone that pancreatitis explained every fight, nor do I have a documented post-treatment outcome to report here. The practical lesson is still substantial: the location and timing of contact can point toward a medical question that a conventional training analysis might overlook.

The same reasoning applies to the urinary tract and other abdominal structures. Straining to urinate, repeated attempts to urinate, blood in the urine, a tense abdomen, or an abrupt change in elimination habits are medical concerns, not reasons to increase correction. A dog with urinary obstruction or severe abdominal illness may need urgent veterinary attention. Conversely, a dog that is ill may be quieter or withdrawn rather than aggressive. Neither the presence nor absence of a bite tells us how severe the underlying disease is. The medical signs, not a theory of aggression, should determine the urgency of the referral.

These examples should not be treated as equally supported explanations of aggression. The veterinary evidence that pancreatitis can cause abdominal pain is much stronger than evidence quantifying how often pancreatitis treatment ends biting incidents. The same distinction applies to dental infection. An infected or fractured tooth is a plausible source of painful handling responses, but a general dental-disease reference does not establish a causal link to a particular attack. My cases provide reasons to ask questions, not estimates of prevalence or treatment success. This is a point where a veterinary coauthor or reviewer could help identify additional case series or controlled studies, if they exist.

Chronic itching belongs in this discussion, although itching and pain are not identical sensations. In a 2022 study involving 141 dogs with atopic dermatitis, investigators found associations between chronic skin disease and higher owner-reported scores for several behavioral measures, including aggression and touch sensitivity [5]. The design did not establish that dermatitis caused attacks or that treating the skin disease would eliminate them. It does, however, broaden the question from a painful joint to the animal’s overall physical comfort.

The practical consequences of severe skin disease can be far more serious than the word “itchy” suggests. In one case, I worked with a Cocker Spaniel whose skin allergies were so severe that touching him could provoke intense aggression. His owners had pursued repeated veterinary treatment: medications, topical products, special baths, and even surgical removal of the ear canals. Despite these interventions, the condition remained intolerable. Ultimately, according to the owner, the veterinarian recommended euthanasia because the dog’s suffering could not be adequately relieved. This was not a story of an owner unwilling to seek treatment, nor a dog whose behavior could be solved by teaching him to accept petting. It was a case in which chronic physical disease and the limits of available relief dominated the animal’s life. I cannot separate the contribution of itch, pain, secondary infection, and learned anticipation of touch, but those distinctions do not diminish the seriousness of the suffering.

In another household, an American Bulldog had begun nipping the children. The dog’s skin and ears were conspicuously pink, and I was concerned that unwanted touching might be provoking defensive responses. The veterinarian confirmed that the dog was very uncomfortable and that the discomfort was contributing to the nipping when touched. This is a different sort of case from the Cocker Spaniel’s: the immediate priority was to protect the children and prevent further unwanted contact while the veterinarian addressed the skin disease. A child cannot be expected to diagnose pain from a dog’s appearance, and even a familiar family dog should not be repeatedly exposed to touching that elicits warning or biting behavior. I do not have enough follow-up information to claim that medical treatment permanently resolved the nipping.

Ear disease deserves special attention within this discussion. Allergic skin inflammation can predispose dogs to painful otitis externa, sometimes complicated by bacterial or yeast infection. Merck’s veterinary review lists pain, itching, redness, swelling, erosions, and discharge among the clinical findings and explains why recurrent disease requires attention to underlying causes [16]. Severe, chronic ear disease may become a problem of both skin and deeper ear structures, and treatment can itself involve repeated uncomfortable handling. The presence of inflamed ears therefore changes how a trainer should interpret resistance to head handling. The McAuliffe questionnaire findings remain valuable evidence of an association between atopic dermatitis and aggression-related scores, but these two clinical histories show why the lived severity of an individual case cannot be read directly from a questionnaire average.

The McAuliffe study is more specific than a general statement about dogs being irritable when uncomfortable. Its 141 affected dogs were older than one year, had clinically diagnosed atopic dermatitis, and had been itching for more than three months. Owners completed the Canine Behavioral Assessment and Research Questionnaire, or C-BARQ. Compared with a large healthy control group, the affected dogs had higher scores for owner-directed, stranger-directed, and familiar-dog aggression, among other outcomes [5]. Yet a questionnaire category called aggression may encompass a range of threats and actions. The paper does not establish the incidence of serious bite injuries, and its cross-sectional comparison cannot determine whether skin disease preceded every behavioral difference.

Some breeds are more susceptible to particular orthopedic, spinal, or other medical disorders. Those predispositions may help a veterinarian decide what to investigate, but they must never be converted into claims that a breed is aggressive because it is prone to disease. The individual dog, its clinical findings, and the circumstances of the incident remain decisive.

I once evaluated a Pug and a French Bulldog that played together without difficulty until their excitement reached a certain point, when the play would escalate into fighting. I suspected that physical discomfort might be contributing to the problem, so rather than beginning behavioral modification, I recommended a veterinary examination. The veterinarian subsequently prescribed medication for what I recall was an orthopedic or spinal pain condition affecting the French Bulldog, although I no longer remember the precise diagnosis or medication. After the dog began receiving veterinary care, the owner reported that the fighting stopped. We never needed another training session. I had been paid for the initial evaluation, but I believed it was important to investigate a possible medical explanation before recommending further lessons. The outcome was consistent with my suspicion that pain had been contributing to the fights, although it could not establish that pain was the sole cause.

What changes after veterinary care?

The most interesting cases are often those in which behavior changes after a veterinarian identifies and manages a painful condition. Daniel Mills and colleagues reviewed interactions between pain and behavioral problems in dogs and cats, describing several possible relationships: pain may directly contribute to an action, aggravate an established difficulty, or coexist with other changes [2]. Their case material includes a dog whose renewed vigilance and stronger responses to people and dogs coincided with gait abnormalities. The owner later reported behavioral improvement during a veterinarian-directed trial of grapiprant, while the existing management program continued. The observation is suggestive; it is not a controlled demonstration that the medication eliminated biting.

The 2020 Mills review deserves more attention because it attempts to organize the clinical problem rather than reduce it to a single disease. Its authors describe pain as a possible direct source of problem behavior, a contributor to secondary problems, an exacerbating influence on existing behavior, or a condition accompanying other signs. This framework accommodates a dog whose first attack occurs during painful handling, another whose long-standing aggression worsens with arthritis, and a third whose learned responses persist after treatment. The paper draws heavily on clinical material and professional interpretation, which makes it useful for generating hypotheses but weaker for estimating population-wide effects [2].

A separate caution concerns species. The review includes cases involving both dogs and cats, and its examples must not be blended into a single canine treatment history. A reported return of aggression following a medication change in a cat cannot be presented as a demonstrated canine result. Where the dog case involving grapiprant is discussed, the relevant observations are the owner’s reported changes in vigilance, reactions, and play, while management continued—not an independently measured disappearance of injurious bites [2].

It is also important to distinguish pain from pruritus, nausea, and other forms of physical distress. These experiences are not interchangeable, and a dog may have more than one at once. A skin-disease case may involve intense itching and painful secondary ear inflammation; a dog with pancreatitis may experience abdominal pain and nausea; a dog with advanced cancer may be weak, painful, or both. Describing all of them merely as “pain aggression” obscures the very mechanisms that a veterinary examination is intended to investigate. The more precise question is whether a particular medical condition altered the dog’s tolerance of contact, movement, or social interaction.

That difference matters. A dog that stops biting after treatment may be more comfortable. It may also be moving less, meeting fewer visitors, or being handled differently. Some medications affect alertness and activity independently of pain relief. A dog who has no opportunity to bite because he is kept apart from everyone has not necessarily become safer. To interpret change responsibly, we need to know what happened to the dog’s normal movement, sleep, social engagement, and opportunities for ordinary interaction—not merely whether the household recorded another incident.

A convincing treatment-response record would therefore have at least two parallel histories. One would describe veterinary findings, physical function, treatment dates, and adverse effects. The other would describe actual aggression: what contact occurred, whether injury resulted, how often comparable situations arose, and what environmental restrictions changed. If a household stops inviting visitors after an attack, the subsequent absence of visitor-directed bites is not a meaningful before-and-after comparison. If a dog resumes ordinary activity without sedation and shows better tolerance of routine handling, that is a more informative observation, though still not a controlled experiment.

Veterinarians have several ways to manage particular painful conditions, including prescription anti-inflammatory drugs. Carprofen, meloxicam, firocoxib, and grapiprant are examples used in dogs under veterinary supervision. They differ in indications and mechanisms, and they carry risks; the U.S. Food and Drug Administration warns that adverse effects of veterinary nonsteroidal anti-inflammatory drugs may involve the digestive tract, kidneys, or liver [9, 10]. Naming them here is reporting veterinary practice, not recommending a drug or suggesting that owners try medication to test an aggression hypothesis.

The AAHA guidelines also show why medication should not be portrayed as a single-purpose switch. Veterinary pain care is an ongoing sequence of assessment, treatment, reassessment, and revision; it may involve environmental adaptation, rehabilitation, exercise planning, weight management, surgery, or pharmacological treatment depending on the diagnosis [8]. A medication may relieve pain, alter arousal, cause sedation, or produce side effects. The presence or absence of biting is only one part of evaluating what has changed. Owners should never start, stop, or alter medication as an aggression experiment.

For years I have informally called my referral-and-observation approach a “pain test.” It is not a medical test that I administer or a validated diagnostic procedure. When the circumstances of aggression raise concern about illness, I refer the dog for veterinary evaluation. If the veterinarian finds and addresses a condition, I pay attention to what changes afterward. Sometimes owners report striking improvement. Sometimes the change is partial; sometimes there is no clear change. The observation helps guide the next behavioral questions, but it does not replace the veterinarian’s judgment or establish a cause by itself.

The strongest version of this observation is not a dramatic before-and-after anecdote but an attributable chronology. Who first noticed the change? What did the veterinarian diagnose? Which behaviors did I observe personally, and which were reported by the owner? Did the dog improve physically? Did aggressive encounters cease because the dog was more comfortable, because the household altered its routines, or because the dog had fewer opportunities to encounter the provoking situation? Sometimes the record cannot answer those questions. Saying so preserves the value of the case without turning uncertainty into a diagnosis.

A careful history also preserves information that is easy to lose after a frightening event: the severity and location of a bite, whether skin was broken, what immediately preceded it, what the dog could do physically, and what happened when similar situations occurred naturally afterward. There is no justification for deliberately recreating a dangerous encounter to see whether a dog will bite again. The comparison must rely on safe, ordinary observation and professional judgment.

When the medical and behavioral histories meet

Suppose a dog repeatedly experiences discomfort when a person reaches for his collar. He may initially try to withdraw. If the person continues and a bite causes the handling to stop, the dog may learn that biting changes the situation. The person’s approach may also become associated with an expectation of discomfort. Even if the original pain improves, the learned response can persist. Medical care and behavioral work are therefore not competing explanations; sometimes both are needed.

The opposite is also true. An established aggression problem may become more severe when a dog develops painful disease. A dog that once tolerated close contact might react sooner when movement hurts. It would be a mistake to interpret the change exclusively through reinforcement, just as it would be a mistake to assume that every aggressive action reveals an underlying medical condition. Learning explains part of the history, not the whole animal.

What if the veterinarian finds no medical explanation? That result is useful, but it is not proof that every conceivable illness has been excluded. Some conditions fluctuate or require further investigation, and the veterinarian determines whether additional testing is appropriate. When the medical questions have been appropriately addressed, behavioral assessment can concentrate on developmental history, social experience, environmental conditions, previous consequences, and the exact sequence surrounding each incident. For serious attacks, management and safety remain necessary regardless of the suspected cause.

The Cocker Spaniel also raises a difficult ethical point that a discussion of treatment success alone would miss. Some diseases remain severe despite extensive and appropriate medical intervention. An animal’s quality of life may deteriorate even when its owners and veterinarians have done everything reasonable to help. Decisions about humane euthanasia belong to the owner in consultation with the veterinarian, informed by suffering, prognosis, realistic treatment options, and safety. A trainer should neither prescribe that outcome nor promise that a behavioral program can overcome uncontrolled physical distress. Recognizing the limits of treatment is not the same as abandoning the animal.

The distinction between medical and behavioral expertise should be clear without becoming a wall between them. I can describe what I saw, ask about changes in movement or handling tolerance, and help the owner assemble an accurate history. The veterinarian examines the animal and makes medical decisions. When the dog is medically ready, a trainer can work on the behavioral problems that remain. Good collaboration means neither professional pretending to do the other’s job.

What the evidence leaves unresolved

There is a substantial difference between a dog that growls during handling, a dog that snaps without contact, and a dog that inflicts a serious bite. Research papers do not always separate these outcomes. Owner questionnaires may measure aggression broadly; studies of arthritis may measure mobility rather than aggression at all. The strongest evidence for pain-related aggression includes clinical cases, but controlled evidence about the disappearance of actual attacks after pain treatment remains limited [1–4].

A 2025 systematic review by Boonhoh and colleagues underscores both the breadth of the question and the thinness of the literature. The authors screened 14,267 records, included 29 studies in their qualitative review, and only four in their meta-analysis. Aggression was the most frequently reported behavioral problem in the included disease literature, appearing in eighteen articles. But the quantitative meta-analysis concentrated on feline immunodeficiency and leukemia virus associations in cats—not on treatment of pain-related biting in dogs. Its pooled feline figures must not be borrowed as canine aggression statistics. The review’s principal relevance here is the fragmented state of research connecting physical illness and behavior [13].

The literature also contains a clinical review by Mills, Coutts, and McPeake on behavior problems associated with pain and paresthesia [4]. Its discussion broadens the possible sensory mechanisms beyond straightforward tissue pain, while remaining a review rather than a controlled canine bite-treatment trial. Reviews synthesize existing evidence; they do not automatically create stronger primary evidence than the studies they cite. Together these papers support serious clinical attention to medical contributors while exposing how little prospective research isolates violent attack outcomes.

An additional complication is selection bias. Dogs referred to specialty behavior services are not a random sample of dogs, and owners who seek specialty care may differ from those who do not. Striking treatment responses are also more likely to be remembered or published than uneventful ones. Figures drawn from behavioral referral populations must not be presented as the percentage of aggressive dogs in the general population that are in pain. Any future case series should include partial and unsuccessful outcomes, not just memorable successes.

The research is difficult for good reasons. Investigators cannot ethically provoke dangerous attacks simply to count them. Owners alter routines after an incident, sometimes dramatically. Medical conditions fluctuate, medications may have multiple effects, and learning histories differ. These limitations should make us careful, not dismissive. A clinical observation may justify further investigation without supporting a universal prediction.

That is why I would be wary of either extreme: the claim that an aggressive dog simply needs firmer correction, or the equally sweeping claim that aggression will disappear once a painful condition is treated. Both bypass the individual dog. Neither gives owners a reliable way to understand what happened.

I still return to the young Labrador lying in his owner’s yard. The neighbor saw the attack and immediately proposed punishment. The veterinarian later found cancer. We cannot reconstruct the dog’s experience, but we can recognize the danger in deciding what an action means before investigating the animal’s condition. In that case, the refusal to get up may have been the most important part of the story—and it was the part most easily mistaken for disobedience.

Glossary

Aggression. Threatening or attack-related actions directed toward another individual; studies vary in whether they count growls, snaps, bites, or injuries. Ethologically, aggression refers to violence, but to normalize the various studies, I had to use their expanded definitions.

Analgesia. Relief or reduction of pain.

Atopic dermatitis. A chronic inflammatory skin disorder commonly associated with itching.

Behavioral assessment. An investigation of a dog’s history, actions, interactions, and environment; not a substitute for veterinary examination.

BASSO pain test. The author’s informal term for veterinary referral followed by observation of behavioral changes; not a validated medical test.

Breed predisposition. A higher relative likelihood of a particular condition in a breed; not evidence that individual dogs will become aggressive.

Chronic pain. Pain that persists or recurs over time and may affect function and welfare.

Confounding factor. Another change, such as reduced exposure or altered handling, that makes an apparent treatment effect harder to interpret.

Defensive aggression. Aggressive actions occurring in the context of perceived threat or unwanted contact.

Intervertebral disc disease. Disorders affecting discs between vertebrae that may cause pain or neurological impairment.

Negative reinforcement. A learning process in which an action becomes more likely because it removes or prevents something unpleasant.

Nociception. Neural detection and processing of potentially damaging stimuli; not identical to the experience of pain.

NSAID. Nonsteroidal anti-inflammatory drug, a medication class used under veterinary oversight for certain painful conditions.

Osteoarthritis. Joint disease associated with structural changes, inflammation, pain, and possible mobility limitations.

Pain-related aggression. Aggressive actions to which pain or anticipated pain may contribute.

Pancreatitis. Inflammation of the pancreas, which may involve abdominal pain and other clinical signs.

Pruritus. Itching.

Treatment-response observation. Documentation of changes after care, interpreted alongside concurrent changes and possible confounders.

Veterinary behaviorist. A veterinarian with specialized training in animal behavior and its medical and environmental interactions.

Visceral pain. Pain originating in internal organs or associated structures; its outward signs may differ from pain involving skin, joints, or muscles.

Otitis externa. Inflammation of the external ear canal, sometimes associated with allergies, infection, itching, and pain.

Periodontal disease. Inflammatory disease affecting the tissues supporting the teeth, potentially associated with infection and oral pain.

References and veterinary resources

1. Camps, T., Amat, M., Mariotti, V. M., Le Brech, S., & Manteca, X. (2012). Pain-related aggression in dogs: 12 clinical cases. Journal of Veterinary Behavior, 7(2), 99–102. https://doi.org/10.1016/j.jveb.2011.08.002

2. Mills, D. S., et al. (2020). Pain and problem behavior in cats and dogs. Animals, 10(2), 318. https://doi.org/10.3390/ani10020318

3. Camps, T., Amat, M., & Manteca, X. (2019). A review of medical conditions and behavioral problems in dogs and cats. Animals, 9(12), 1133. https://doi.org/10.3390/ani9121133

4. Mills, D. S., Coutts, F. M., & McPeake, K. J. (2024). Behavior problems associated with pain and paresthesia. Veterinary Clinics of North America: Small Animal Practice, 54(1), 55–69. https://doi.org/10.1016/j.cvsm.2023.08.007

5. McAuliffe, L. R., Koch, C. S., Serpell, J., & Campbell, K. L. (2022). Associations between atopic dermatitis and anxiety, aggression, and fear-based behaviors in dogs. Journal of the American Animal Hospital Association, 58(4), 161–167. https://doi.org/10.5326/JAAHA-MS-7210

6. Anderson, K. L., et al. (2018). Prevalence, duration and risk factors for appendicular osteoarthritis in a UK dog population under primary veterinary care. Scientific Reports, 8, 5641. https://doi.org/10.1038/s41598-018-23940-z

7. Wright, A., et al. (2022). Identification of canine osteoarthritis using an owner-reported questionnaire and treatment monitoring using functional mobility tests. Journal of Small Animal Practice, 63(8), 609–618. https://doi.org/10.1111/jsap.13500

8. American Animal Hospital Association. (2022). 2022 AAHA Pain Management Guidelines for Dogs and Cats. https://www.aaha.org/resources/2022-aaha-pain-management-guidelines-for-dogs-and-cats/

9. U.S. Food and Drug Administration. Get the Facts about Pain Relievers for Pets. https://www.fda.gov/animal-veterinary/animal-health-literacy/get-facts-about-pain-relievers-pets

10. U.S. Food and Drug Administration. Controlling Pain and Inflammation in Your Dog with Nonsteroidal Anti-Inflammatory Drugs. https://www.fda.gov/animal-veterinary/animal-health-literacy/controlling-pain-and-inflammation-your-dog-nonsteroidal-anti-inflammatory-drugs

11. Merck Veterinary Manual. Pancreatitis and other disorders of the pancreas in dogs. https://www.merckvetmanual.com/dog-owners/digestive-disorders-of-dogs/pancreatitis-and-other-disorders-of-the-pancreas-in-dogs

12. Comparison of Clinical Features of Intervertebral Disc Extrusions in English Cocker Spaniels, French Bulldogs and Dachshunds. (2025). https://pmc.ncbi.nlm.nih.gov/articles/PMC11851645/

13. Boonhoh, W., Poolkhet, C., Waran, N., & Wongtawan, T. (2025). Systematic review and meta-analysis of the occurrence and association of physical diseases and behavioural problems in dogs and cats. Applied Animal Behaviour Science, 291, 106717. https://doi.org/10.1016/j.applanim.2025.106717

14. American Animal Hospital Association. (2019). 2019 AAHA Dental Care Guidelines for Dogs and Cats. https://www.aaha.org/resources/2019-aaha-dental-care-guidelines-for-dogs-and-cats/

15. Steiner, J. M. (2025). Pancreatitis in Dogs and Cats. Merck Veterinary Manual (professional edition; peer reviewed). https://www.merckvetmanual.com/digestive-system/the-exocrine-pancreas/pancreatitis-in-dogs-and-cats

16. Hoff, S. (2025; updated 2026). Otitis Externa in Animals. Merck Veterinary Manual (professional edition; peer reviewed). https://www.merckvetmanual.com/ear-disorders/otitis-externa/otitis-externa-in-animals

17. American Animal Hospital Association. (2026). Pancreatitis in Dogs and Cats: Signs, Causes, Treatment, and Prevention. https://www.aaha.org/resources/understanding-pancreatitis-in-pets/

Disclaimer: This article reports veterinary research and professional dog-training observations for educational purposes. It is not veterinary medical or legal advice. Diagnosis and medical care belong to licensed veterinary professionals. Serious aggression requires appropriate safety precautions and professional assessment.