Pain Masking in Dogs: Why Discomfort Is Hard to See

1. The Problem in One Sentence

1.1 Pain Shows Up as Behavior

Dogs do not report pain in words. What they do is behave differently, and the change is often subtle, gradual and easy to attribute to something else. A review of medical conditions and behavior problems puts it plainly: one of the most important signs of pain in animals is a change in behavior, and those signs include both the loss of normal behaviors and the appearance of new ones (Camps, Amat & Manteca, 2019).

That single fact explains why pain is missed. The household is often not looking for a visible limp; it is living with a dog that has become slightly less keen on the stairs, a little grumpier with the other dog, and harder to settle in the evening.

1.2 Why "Masking" Is a Loaded Word

The popular explanation is that dogs hide pain to avoid appearing weak to predators or rivals. That story is repeated everywhere and is difficult to test. What can be observed is simpler and does not require an evolutionary motive: many painful conditions develop slowly, dogs adapt their movement and routines around them, and the signs that remain are ambiguous.

This article uses "masking" in that descriptive sense — pain that is present and not obvious — rather than as a claim about why dogs behave as they do.

1.3 How to Read the Evidence

Most of what follows comes from clinical work: review papers, case series from behavior referral practices, and large primary-care datasets. That is the nature of the field. Each section says what kind of evidence stands behind the claim (why the type of evidence shapes the claim).

1.4 Why This Matters for Trainers

A dog whose behavior is influenced by pain may receive weeks or months of training while the underlying condition remains unrecognized, reducing the chance that training alone will succeed. The household loses money and confidence, the trainer's method appears to fail, and the dog spends that time hurting. That is the practical case for taking this seriously, and it does not require anyone to practice veterinary medicine.

The reverse error is cheaper. A dog sent for a veterinary check that turns out to be healthy has lost one appointment; the training then proceeds with one differential excluded.

1.5 Acute and Chronic Are Different Problems

Acute pain is usually obvious: the dog yelps, limps, stops eating, or reacts sharply to being touched in one place. Chronic pain is the problem this article is about. It builds slowly, the dog adapts around it, and the signs blend into everyday behavior.

That difference also explains why owners often report no pain when asked directly. They are answering about the acute picture, which their dog does not show.

2. How Common Is This

2.1 Pain in Behavior Caseloads

Estimates of how often medical factors contribute to behavior cases have risen over the decades. An early report indicated a prevalence of around 5 percent; a later figure was 12 percent in dogs and 19 percent in cats; an unpublished review of a referral caseload in 2013 returned 23 percent for dogs, and the authors of a 2020 review describe this as at the lower end of what has since been reported across a wider geographic base. Across the practices they reviewed, the proportion of presented dogs with a painful condition involved ranged from 28 to 82 percent, conservatively estimated at around one third (Mills et al., 2020).

Those numbers are not population prevalence. They describe referral caseloads, where difficult cases concentrate. What they show is a trend: the more carefully clinicians look, the more often pain turns up.

2.2 One Painful Condition in the General Population

Osteoarthritis gives a sense of scale. In a VetCompass analysis of 455,557 UK dogs under primary veterinary care, the estimated annual period prevalence of appendicular osteoarthritis was 2.5 percent, equating to roughly 200,000 affected dogs in one year. Risk factors included certain breeds, neutering, higher bodyweight and age over eight years, and the condition was calculated to affect around 11.4 percent of an affected dog's lifespan (Anderson et al., 2018).

That is one diagnosed condition, in dogs that were brought to a practice, in one country. Dental disease, soft-tissue injuries, gastrointestinal pain and neurological pain add to the picture (how internal pain shows itself).

2.3 The Practical Reading

Pain is clinically relevant, chronic pain can affect a substantial period of a dog's life, and behavior is one important channel through which it may become visible. A trainer or behavior consultant who never finds pain in their caseload is probably not finding it rather than not having it.

2.4 What the Numbers Cannot Say

None of these figures tells a household how likely it is that their particular dog's problem involves pain. Referral caseloads are selected, primary-care records capture only diagnosed conditions, and many painful conditions are never recorded because nobody brought the dog in for them.

Used properly, the numbers do one job: they move pain from the category of rare explanation to the category of routine consideration.

2.5 Age Is Not a Diagnosis

Osteoarthritis was diagnosed at an average age of around ten and a half years in the UK dataset, and being older than eight years was a risk factor (Anderson et al., 2018). Households hear this as confirmation that slowing down is just age. The finding says the opposite: age raises the probability that a painful condition is present, not that a change needs no explanation (what else changes in older dogs).

2.6 Why the Estimates Have Risen

The rise from around 5 percent to figures above 20 percent in behavior caseloads is unlikely to reflect dogs becoming more painful. The more plausible explanations are that clinicians now look for pain deliberately, that diagnostic access has improved, and that the concept of maladaptive pain has entered behavioral medicine (Mills et al., 2020).

That has a direct implication for anyone reading an older textbook or an older course: the figure they learned was probably an artifact of not looking.

3. What Pain Looks Like

3.1 Lost Behaviors

The review literature groups the signs into two kinds. Lost normal behaviors include decreased activity or movement, less interaction with people or other animals in the household, a lethargic manner, reduced appetite and reduced resting behavior (Camps et al., 2019).

Loss is harder to notice than addition. A dog that stops doing something does not create an incident, and households often describe the change as the dog getting older or calmer.

3.2 New Behaviors

The second group covers behaviors that appear: aggression, fear responses, house soiling, vocalization, altered facial expression, altered posture, restlessness and hiding (Camps et al., 2019). These do create incidents, which is why they reach a trainer — usually described as a behavior problem rather than a medical one.

3.3 What Belongs on the Differential

From a clinical standpoint, pain should be included in the differential diagnoses for aggression, fear and phobia responses, sleep disturbances, inappropriate elimination, vocalization and repetitive behaviors (Camps et al., 2019). That is a wide list, and it is the reason a medical check belongs early rather than after a training plan has failed (where repetitive behavior comes from).

3.4 Why the Clinic Is the Worst Place to See It

Subtle behavioral changes may not be apparent to veterinary staff in a consulting room, where fear, excitement or anxiety can override them. A dog that has been reluctant to jump into the car all month will trot cheerfully across the practice floor on adrenaline, and the examination finds nothing (why behavior in the clinic is not representative).

3.5 Adaptation Hides the Signs

Dogs may redistribute load and change movement strategies before obvious lameness becomes visible. A dog with hip pain may sit down differently, take stairs in a rush to get them over with, or stop shaking off after a wet walk. Owners see a dog moving normally and a few odd habits, not a symptom.

That is the mechanical version of "masking" and it needs no evolutionary story: adaptation is what bodies do, and it works well enough to keep the problem out of sight for months.

3.6 Intermittent Pain Is Especially Deceptive

Many painful conditions fluctuate. The dog is stiff after rest and loosens up with movement, is worse in cold weather, or has a bad week after a long walk. A household that sees a good day concludes the problem is behavioral, and a consultation on a good day finds nothing.

Day-to-day inconsistency is therefore not evidence against pain. It is one of the patterns that should raise suspicion.

3.7 Touch and Handling

Changes around handling — flinching at the collar, avoiding being picked up, growing intolerant of grooming in one area, or objecting to being lifted onto a table — are among the most direct signals available, and they are frequently read as the dog becoming difficult (how handling can be arranged).

3.8 Facial Expression and Posture

Altered facial expression and altered posture are on the list of behaviors that appear with pain (Camps et al., 2019). In practice they are the signs most often noticed in retrospect, once someone looks at old photographs or videos: a tighter face, ears held differently, a slightly tucked stance, a weight shift away from one side.

That retrospective recognition is why home video taken now is worth more than a description. It gives the next assessment something to compare against.

4. The Noise Sensitivity Case

4.1 The Study

One of the clearest demonstrations that pain changes the shape of a behavior problem comes from a comparison of clinical records at a university behavior clinic. Twenty cases of noise sensitivity were examined: ten in which musculoskeletal pain was identified, and ten without (Lopes Fagundes, Hewison, McPeake, Zulch & Mills, 2018).

4.2 What Differed

Loud noises as a trigger appeared in both groups but were present in every case where pain was involved. In those cases, the age at which the noise sensitivity began was on average nearly four years later than in the cases without pain. Two further themes emerged only in the pain group: widespread generalization to associated environments, and avoidance of other dogs (Lopes Fagundes et al., 2018).

In this small case series, several dogs improved after pain was identified and treated.

4.3 Why This Matters Beyond Noise Sensitivity

Three features of the pain group are useful as general warning signs: a late onset for a problem that usually starts younger, an unusually wide spread of the fear to places and situations, and avoidance of other dogs that were previously unremarkable. A dog in pain has a reason to avoid unpredictable bumping and jostling, which fits the pattern (what is known about noise sensitivity).

4.4 The Reach of the Study

Twenty cases from one referral clinic, analyzed qualitatively. The findings are a strong prompt for clinical attention and not a prevalence estimate or a diagnostic test.

4.5 Why Pain Widens a Fear

The generalization finding fits what is known about learning under aversive conditions: an animal in a heightened state forms broader associations, and a dog that is uncomfortable has less capacity to discriminate between the specific trigger and everything around it. That is a plausible interpretation rather than a directly tested mechanism. It explains why pain cases looked less like a tidy conditioned fear and more like a general avoidance of places and company (how fear associations form).

The practical consequence is that a desensitization plan that targets only the original noise may make little progress while the underlying condition continues (how fear responses are changed).

4.6 What the Pain Group Had in Common

Reading the two groups side by side, the dogs with pain were not more afraid of noise; they were afraid of more things, in more places, and for longer, and their problem had started at an age when most dogs' noise sensitivity is already established (Lopes Fagundes et al., 2018). The distinguishing feature was the shape of the problem rather than its intensity.

That is a useful reframing for intake: instead of asking how bad the fear is, ask how wide it has become and when it began.

5. Why Detection Fails

5.1 Three Kinds of Difficulty

A case series of ten dogs referred to a behavior practice sorted the diagnostic challenges into three categories: bias in observation, limitations of the clinical examination, and interpretation of behavioral signs (Kwik, De Keuster, Bosmans & Mottet, 2025). Each is worth spelling out, because each is fixable in a different way.

5.2 Observation Bias

Owners see their dog daily, which makes gradual change nearly invisible, and they interpret what they see through an existing story: he's stubborn, she's always been anxious, he's just getting old. Signs that fit the story get noticed and signs that do not get explained away.

5.3 The Examination Misses It

Clinical signs of maladaptive pain are often non-specific and may be absent during the examination itself (Kwik et al., 2025). A normal orthopedic exam on a particular afternoon does not exclude a painful condition that shows itself on stairs at home, after exercise, or in the second half of the night.

5.4 Signs Get Interpreted as "Purely Behavioral"

Certain signs are routinely dismissed as behavioral. The authors give pica as an example: in two of their cases, dogs that had undergone repeated intestinal surgery illustrated that pica can also be associated with musculoskeletal pain rather than only with gastrointestinal or behavioral causes (Kwik et al., 2025).

5.5 What the Case Series Found

In their ten cases, all dogs were diagnosed with altered socioemotional functioning. In seven of ten, the structured approach indicated maladaptive pain, confirmed by imaging in three of those seven, and multimodal treatment led to recovery in six of the seven. In three dogs with an existing behavioral history, an acute worsening of signs suggested maladaptive pain, confirmed by imaging in all three (Kwik et al., 2025).

Ten selected cases from the authors' own practice cannot establish how often this happens. What they demonstrate is a workable method and the size of the difference it made for these dogs.

5.6 The Owner's Story Is Data, Not Noise

Observation bias cuts both ways. Owners miss gradual change, and they also hold the only long-term record of the dog's behavior that exists. The task is not to distrust the household but to ask questions that bypass the story: what did the dog do a year ago that it does not do now, which of these things happened first, and what does a normal evening look like?

5.7 Why a Single Consultation Is Not Enough

Between the dog's adaptation, the fluctuating course of many conditions and the arousal of the clinic visit, one appointment samples a narrow and unrepresentative slice. Repeated observation over time, ideally recorded at home, is what the structured approaches in this literature rely on (Kwik et al., 2025).

5.8 Fear of the Clinic Compounds It

A dog that is frightened at the practice is harder to examine, which limits what a physical examination can find and makes the examination itself more aversive. Over repeated visits that becomes its own problem, on top of the one that brought the dog there (what arousal does to observation).

5.9 The Structured Alternative

The approach described in the case series combines caregiver questionnaires, medical history, home video analysis, clinical observation and a timeline, with behavioral signs sorted into adaptive and maladaptive categories to guide differential diagnosis (Kwik et al., 2025). None of those components is expensive; what they require is that somebody collects them systematically rather than relying on a single consultation.

For a trainer, three of the five are directly available: the history, the home video and the timeline. Supplying those to the veterinarian is the most useful contribution available from outside the practice.

5.10 Why Owners Say "He Doesn't Seem to Be in Pain"

Households are answering an honest question honestly: their dog does not whimper, does not limp visibly, eats, and greets them. Those are the signs of acute pain, and chronic pain rarely produces them. Rephrasing the question — what has your dog stopped doing this year — usually produces a different and more useful answer within a minute.

That reframing is also kinder. Owners who later learn their dog was in pain for months often blame themselves; the literature is clear that these signs are hard to see from the inside (Kwik et al., 2025).

6. Signals Worth Taking Seriously

6.1 Change Without an Obvious Cause

The strongest single indicator is not a particular behavior but a change: something the dog used to do and no longer does, or something new that has appeared, without a corresponding change in the household, the routine or the training.

6.2 Sudden Aggression in a Dog That Was Not Aggressive

Aggression that appears in an adult dog with no history of it, particularly around handling, being approached while resting, or specific body areas, belongs on a medical differential before a training one. Pain lowers the threshold for defensive responses, and the dog is not "turning on" anyone (how pain and aggression are connected).

6.3 Reluctance Around Specific Movements

Hesitating at stairs, avoiding the car, no longer jumping onto the sofa, sitting crookedly, standing up in stages, or shifting position frequently while resting are all movement-related signs. They are easy to attribute to age, and age is not an explanation in itself.

6.4 Changes in Rest

Reduced resting behavior appears among the lost normal behaviors associated with pain (Camps et al., 2019). A dog that circles for a long time before lying down, changes position repeatedly, sleeps in new places or is restless at night is describing something about lying down (how canine rest is organized).

6.5 Training That Stops Working

A dog that could do something and now cannot, or a training plan that was progressing and has stalled without explanation, is a practical reason to consider possible contributing factors, including pain. Motivation, movement and concentration all suffer when something hurts.

6.6 Changes in Social Behavior at Home

Reduced interaction with people or other animals is on the list of lost normal behaviors (Camps et al., 2019). In multi-dog households this often surfaces as new friction: a dog that used to tolerate being walked over now objects, or avoids the other dog's play invitations and then snaps when pressed (how conflict develops between dogs in one home).

6.7 Toileting and Vocalization

House soiling and increased vocalization both appear among the behaviors associated with pain (Camps et al., 2019). Both are also classic behavior-problem presentations, which is precisely the point: the presentation does not identify the cause.

6.8 Restlessness in the Evening

An evening pattern of not settling, shifting position, pacing and starting things is often read as too little exercise. In a dog with chronic pain, the day's activity is the reason the evening is uncomfortable (why more exercise is not always the answer).

6.9 Young Dogs Are Not Exempt

Pain is associated with age in the population data, and individual young dogs have injuries, developmental orthopedic conditions, dental problems and gastrointestinal pain. A behavior change in a young dog that does not fit the developmental picture deserves the same question as one in an old dog (what is expected during adolescence).

6.10 Sensitivity to Being Left Alone

A dog that becomes less able to cope with being alone can be reacting to discomfort that is worse when nobody is there to interrupt it, to disturbed rest, or to a general reduction in its capacity to cope. Pain belongs on the differential here as in other presentations (how separation-related behavior is assessed).

6.11 Sudden Sensitivity to Being Approached While Resting

A dog that has begun to react when someone approaches its bed, steps over it or sits down next to it is showing a pattern that fits both a learned resource or space conflict and a dog that anticipates being disturbed while uncomfortable. The two look alike from the doorway, and the difference is usually in the rest of the picture: how the dog lies down, how it gets up, and what else has changed in the same period.

7. Pain or Behavior: Telling Them Apart

7.1 The Question Is Usually Not Either-Or

Pain and learning interact. A dog that has been hurt while being handled learns something about handling; the fear remains after the pain is treated. In the case series, dogs were diagnosed with altered socioemotional functioning and, in most cases, maladaptive pain as well (Kwik et al., 2025). Both need addressing (why the mechanism changes the plan).

7.2 What Points Toward Pain

Late onset relative to the usual pattern for that problem, wide generalization, avoidance of contact and of other dogs, changes around movement or rest, inconsistency from day to day, and a response that seems disproportionate to the trigger.

7.3 What Points Toward Learning

A clear history of the behavior working, consistency across days, a tight link to specific situations rather than to physical contexts, and a pattern that matches the household's responses.

7.4 Why the Distinction Cannot Be Made From Behavior Alone

The overlap is large, and none of the signs above is specific. The realistic approach is not to diagnose from behavior but to recognize when the pattern warrants a veterinary workup, and to say so early.

7.5 Two Cases That Look the Same

Case one. A five-year-old dog has growled at the children twice in a month when they approached its bed. Nothing else has changed. It has always been a little reserved with them, the growling follows a period in which the children have been home more, and it stops when they leave the dog alone.

Case two. A five-year-old dog has growled at the children twice in a month when they approached its bed. It also takes longer to get up, has stopped greeting them at the door, and has been reluctant on the stairs since spring.

The described incident is identical. The second case has three lost behaviors and a timeline, which moves it to a veterinary workup first. That is the whole of the practical skill involved: not judging the growl, but asking what else is different.

7.6 When Treatment Reveals the Answer

In the case series, multimodal treatment led to recovery in six of the seven dogs in whom maladaptive pain was indicated (Kwik et al., 2025). A response to treatment is informative after the fact, and it is not a reason to run an analgesic trial without a proper workup — improvement can also reflect time, changed handling or the household's changed expectations.

7.7 Two Errors With Opposite Costs

Treating pain as a behavior problem costs the dog time in pain and the household a failing plan. Treating a behavior problem as pain costs a consultation and a delay. Those costs are not symmetrical, which is the whole argument for checking early rather than late.

8. What Follows for Practice

8.1 Ask About the Timeline

When did it start, what else changed at that time, and has it got worse in steps or gradually? A timeline is part of the structured approach used in the case series (Kwik et al., 2025), and it is the single most informative thing a trainer can collect.

8.2 Use Video From Home

Home video analysis is part of the same approach (Kwik et al., 2025). It shows movement, rest, stairs and the behavior in its own context, none of which survives the trip to a consulting room.

8.3 Refer Early, Not After Failure

Where the pattern includes any of the warning signs above, a veterinary workup belongs at the start. Months of training with a dog that hurts are months the dog spends in pain, and the training outcome is poor as well.

8.4 Describe, Do Not Diagnose

Trainers are not diagnosing pain. What they can do is describe what they observe precisely — which movements, which situations, what changed and when — and pass that to the veterinarian in a form that is useful.

8.5 Treat the Trial Seriously

Where a veterinarian runs an analgesic trial, the observations that matter come from home over the following weeks: the behaviors the household reported, not just lameness. Deciding in advance what would count as improvement prevents the result from being read as a general impression.

8.6 What to Tell a Household

Four sentences cover it. Pain in dogs usually shows up as changed behavior rather than as obvious signs of hurting. Things your dog has stopped doing matter as much as new problems. A normal examination on one day does not rule pain out. And if the behavior changed without an obvious reason, the veterinarian comes before the training plan.

8.7 What to Write Down

Before a veterinary appointment, a short list is worth more than a long description: what changed, when it started, what the dog has stopped doing, which movements it avoids, how it lies down and gets up, whether there are good and bad days, and what makes it worse. Add two or three short videos from home.

8.8 Where Training Still Belongs

Identifying pain does not make the training work unnecessary. The learned part of the problem — the fear of being handled, the avoidance of the stairs, the growl that has now worked several times — remains after treatment and needs its own plan (why both parts need addressing).

8.9 Medication and Behavior

Where a veterinarian treats pain and a behavior plan runs alongside it, the two interact: a dog in less pain can learn better, tolerate more and recover faster. The same logic applies in reverse to behavioral medication, which is a veterinary decision and not a substitute for finding a physical cause (how behavioral medication is used).

8.10 Working With the Veterinary Practice

The most productive version of this is a short written handover rather than a message that the trainer suspects pain: the timeline, the list of lost and new behaviors, the movements the dog avoids, and the videos. That gives the practice something to examine against, and it keeps the roles clear — observation from the trainer, diagnosis from the veterinarian.

Where a practice is not receptive to behavioral observations, the fallback is the same information given to the household in writing, so that they can present it themselves.

8.11 What Not to Do

Do not run an analgesic trial on a household's own initiative, do not interpret a dog's tolerance of handling as proof that nothing hurts, and do not treat a single unremarkable examination as a closed question when the behavioral picture keeps pointing the other way.

8.12 Keeping the Household on Board

Sending a household to the veterinarian in the middle of a behavior consultation can feel to them like being turned away. Explaining why — that pain is common, that it shows up as behavior, and that a plan built on the wrong cause wastes their time — usually turns it into the opposite: the sense that someone is finally looking at the whole dog.

9. Summary at a Glance

Behavior is the main sign of pain — Including both the loss of normal behaviors and the appearance of new ones (Camps et al., 2019).

Medical involvement in behavior cases has been reported more often over time — From around 5 percent in early reports to 23 percent in one 2013 referral caseload, and higher in more recent reports (Mills et al., 2020).

Osteoarthritis alone affected an estimated 2.5 percent of UK dogs in a year — Around 200,000 dogs, and about 11.4 percent of an affected dog's lifespan (Anderson et al., 2018).

Noise sensitivity looked different when pain was involved — Onset nearly four years later on average, wider generalization, and avoidance of other dogs (Lopes Fagundes et al., 2018).

Signs are often absent during the examination — Which is why a normal consultation does not exclude pain (Kwik et al., 2025).

Structured assessment found pain in most of a selected case series — Indicated in seven of ten dogs, confirmed by imaging in three of those seven, with recovery in six (Kwik et al., 2025).

9.1 One Caution About Red Flags

Lists of warning signs are useful and they invite overreach in both directions. Not every aggressive dog is in pain, and treating every behavior case as a suspected medical case would be its own error, delaying work that the dog needs and adding cost. The claim in this article is narrower: where a change has occurred without an obvious cause, or where the pattern includes loss of normal behaviors, movement-related avoidance or unusual generalization, the medical question comes first.

9.2 How the Findings Fit Together

The four strands agree. Pain expresses itself as behavior and belongs on a wide differential (Camps et al., 2019). Its contribution to behavior caseloads has been reported more often as clinicians look harder (Mills et al., 2020). It changes the shape of a specific problem in ways that can be recognized (Lopes Fagundes et al., 2018). And a structured assessment across history, video and timeline finds cases that a single consultation misses (Kwik et al., 2025). Together they describe a problem of detection rather than of rarity.

10. Research Gaps and Critical Appraisal

Prevalence in the general population is unknown. The figures come from referral caseloads, where difficult cases concentrate (Mills et al., 2020).

The evolutionary explanation is untested. The idea that dogs conceal pain to avoid appearing vulnerable is plausible and not demonstrated.

Case series are small and selected. Ten and twenty cases respectively, from the authors' own practices (Kwik et al., 2025; Lopes Fagundes et al., 2018).

No validated screening tool exists for trainers. The red flags in this article are clinical judgment, not a scored instrument.

Analgesic trials are rarely studied systematically. How often behavior improves under pain treatment, and by how much, has not been quantified in a controlled design.

10.1 What Would Move the Field

Three things. Prospective studies in general behavior caseloads, rather than referral practices, to estimate how often pain contributes. Controlled analgesic trials with behavioral outcomes defined in advance. And a validated screening instrument that non-veterinary professionals could use to decide when to refer, which currently does not exist.

Behavioral outcome measures are not standardized. Studies of pain treatment typically report lameness and mobility scores; the behavioral changes that brought the dog to a trainer are rarely among the outcomes.

11. Conclusion

Pain in dogs is common, and it usually announces itself as behavior rather than as an obvious sign of hurting. The most frequent indication of pain in animals is a change in behavior, covering both behaviors that disappear — movement, interaction, appetite, comfortable rest — and behaviors that appear, such as aggression, fear, vocalization, restlessness and hiding (Camps et al., 2019). Osteoarthritis alone was estimated to affect 2.5 percent of UK dogs under veterinary care in a year, for around a ninth of an affected dog's life (Anderson et al., 2018), and medical involvement in behavior caseloads has been reported at rising rates as clinicians have looked more carefully (Mills et al., 2020). Detection fails for reasons that are now well described: owners cannot see gradual change in a dog they live with, the examination often finds nothing because signs are absent in the consulting room, and certain signs get filed as purely behavioral (Kwik et al., 2025). The noise sensitivity comparison shows what pain does to the shape of a problem — later onset, wider generalization, avoidance of other dogs (Lopes Fagundes et al., 2018). For practice the conclusion is not that trainers should diagnose pain but that they should suspect it early, describe what they see precisely, take a timeline, use home video, and send the dog to a veterinarian before, not after, a training plan has failed.

Key Insights (Takeaways)

• Behavior change is the main sign of pain, and disappearing behaviors are as informative as new ones (Camps et al., 2019).

• A normal veterinary examination does not exclude pain, because signs are frequently absent in the clinic (Kwik et al., 2025).

• Late onset, wide generalization and new avoidance of other dogs distinguished noise-sensitivity cases with pain (Lopes Fagundes et al., 2018).

• Aggression that appears in an adult dog without a history belongs on a medical differential first.

• Osteoarthritis alone is common enough to make chronic pain a routine consideration (Anderson et al., 2018).

• Timeline and home video are the two most useful things a trainer can contribute.

• Pain and learned behavior usually coexist, so treating one rarely removes the other.

References

Anderson, K. L., O'Neill, D. G., Brodbelt, D. C., Church, D. B., Meeson, R. L., Sargan, D., Summers, J. F., Zulch, H., & Collins, L. M. (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

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

Kwik, J., De Keuster, T., Bosmans, T., & Mottet, J. (2025). Detection of maladaptive pain in dogs referred for behavioral complaints: Challenges and opportunities. Frontiers in Behavioral Neuroscience, 19, 1569351. https://doi.org/10.3389/fnbeh.2025.1569351

Lopes Fagundes, A. L., Hewison, L., McPeake, K. J., Zulch, H., & Mills, D. S. (2018). Noise sensitivities in dogs: An exploration of signs in dogs with and without musculoskeletal pain using qualitative content analysis. Frontiers in Veterinary Science, 5, 17. https://doi.org/10.3389/fvets.2018.00017

Mills, D. S., Demontigny-Bédard, I., Gruen, M., Klinck, M. P., McPeake, K. J., Barcelos, A. M., Hewison, L., Van Haevermaet, H., Denenberg, S., Hauser, H., Koch, C., Ballantyne, K., Wilson, C., Mathkari, C. V., Pounder, J., Garcia, E., Darder, P., Fatjó, J., & Levine, E. (2020). Pain and problem behavior in cats and dogs. Animals, 10(2), 318. https://doi.org/10.3390/ani10020318