Recognizing Pain in Cats

Breed Identification

Recognizing Pain in Cats

FĒLIS Editorial Feb 2026 18 min read

No domesticated animal is better at hiding pain than a cat. How good are they at it? A cat with complete urethral obstruction can sit quietly in its bed while its bladder is on the verge of rupturing, and the only sign might be biting the owner's hand when they touch its abdomen, which then gets recorded as "aggressive behavior."

The Old Debt of Veterinary Education

Before the mid-1990s, a judgment circulated through clinical teaching in British and American veterinary schools: cats are less sensitive to pain than dogs. This judgment was wrong. Cats and dogs share the same types of nociceptors and nerve fiber conduction systems, and the pain processing mechanisms in the spinal dorsal horn show no fundamental species-level differences. The judgment came from behavioral misreading. Dogs whimpering after surgery were read as "in pain." Cats curling up after surgery were read as "sleeping."

The consequences were concrete. Before 2000, the proportion of cats receiving post-operative analgesia after spay surgery in North America was far lower than that of dogs. A phrase appeared repeatedly in nursing records: patient resting comfortably. A cat that had just had its abdominal cavity opened and its ovaries and uterus removed, curled motionless in the corner of a cage, was documented as comfortable. That phrase was practically auto-filled in veterinary nursing records of the era. Nobody stopped to think about what it actually meant when an animal that had just undergone abdominal surgery was balled up and motionless.

AAHA and WSAVA later published dedicated guidelines for feline pain management, and veterinary school curricula were updated. The gap between publishing guidelines and updating attitudes is long. A veterinarian who completed residency training in 1990 may still be practicing in 2025. Thirty-five years of clinical inertia does not get erased by a PDF. Cat owners' awareness lags behind the veterinary profession by yet another generation.

This history's effect on the present: the chain is broken from upstream.

The Ear Problem with FGS

Feline Grimace Scale. Five facial action units scored, maximum 10 points, 4 or above suggests the need for analgesic intervention. The tool itself is solid. What follows is not an overview of this tool. It is about where it most commonly goes wrong in a home setting.

The trouble with the ear scoring unit is that it looks too much like a fear expression. When a cat is fearful, the ears press flat backward, tight against the skull, with the inner surface of the pinna nearly invisible from the front. When a cat is in pain, the ears do something different: they rotate outward. The ear tips point laterally and posteriorly, the pinna has an outward-turning angle, and from the front you can see part of the pink inner skin. With a phone photo taken at a slightly off angle, these two ear positions can look identical.

The way to distinguish them is dynamic observation. A fearful cat's ears track the direction of the threat source. You walk from its left to its right, and the direction of the ear flattening follows. A painful cat's ear rotation is constant and does not shift with environmental stimuli. This distinction has never appeared in the official FGS quick-use guide. It has been mentioned in passing in a few of Steagall's team's subsequent application studies, but has never been highlighted as a standalone operational point.

The impact of this omission is bigger than it looks. In a home environment, "threat sources" for a cat are everywhere: unfamiliar visitors, new furniture, a stray cat outside the window. A cat that simultaneously has chronic pain and environmental anxiety will produce mixed ear signals. If the assessor does not know that fear ears are tracking and pain ears are constant, the two signals get blurred together and the resulting score is meaningless.

The whisker scoring unit has a lower error rate. Relaxed and fanned out in a natural spread when pain-free, pulled forward and bunched together, taut, when in pain. The physiological basis is that the muscles at the whisker roots are innervated by the motor branch of the trigeminal nerve, and the pain afferent and motor efferent pathways have synaptic connections in the brainstem. When pain signals come in, this reflex arc causes a change in whisker muscle tension. The cat has very little voluntary control over this response, making it harder to fake than ear position.

On whiskers there is another detail worth mentioning. Many shorthaired cats have white or light-colored whiskers, and in good lighting it is easy to observe the degree of bunching. The problem with longhaired cats is that the fur on both cheeks often obscures the whisker roots. All you can see is the middle and tip of the whiskers, while the tension change at the root is hidden behind fur. The situation is even more complicated with flat-faced breeds like Persians and Exotic Shorthairs. Their facial bone structure means the whiskers sit in a more forward and tense default position, and using FGS reference images as a comparison will systematically overestimate pain scores. The FGS validation studies used predominantly domestic shorthaired cats, and applicability to flat-faced breeds has not been independently validated. Anyone with a Persian or Exotic Shorthair who wants to use FGS needs to at least know about this limitation.

FGS works well for acute pain assessment. Its sensitivity drops significantly for chronic pain. A cat in long-term pain has facial muscle tension patterns that have become the new baseline state. Without having seen its face when it was pain-free, there is no reference.

Breathing

Breathing is the only physiological channel a cat cannot voluntarily manipulate. It is an autonomic rhythm controlled by the medullary respiratory center, beyond the reach of the cat's behavioral masking system.

Somatic pain

Normal resting respiratory rate for a cat is approximately 15 to 30 breaths per minute, predominantly abdominal. When somatic pain (from bone, joint, muscle sources) enters the picture, the rate increases and the depth decreases, because deep breathing pulls on the pain source and the body automatically switches to a shallow-fast strategy.

Visceral pain

Visceral pain (cystitis, pancreatitis, and similar conditions) produces a different pattern: the respiratory rhythm becomes irregular, with intermittent sigh-like deep inhalations followed by a pause after exhalation that is longer than normal.

These pattern differences have diagnostic value in a clinical setting. In a home setting they have almost no practical operability. The reason is simple: you need to first know what this cat's breathing normally looks like. During light sleep, watch the rib cage or abdominal rise and fall, count for 30 seconds and multiply by two, average over three consecutive days. That is the baseline. Without that number, everything said above about respiratory assessment has no anchor.

There is one easily overlooked confounding factor: purring. Cats also purr when in pain. This is something many people do not know. Purring is not exclusively a signal of contentment and relaxation. Cats activate purring under stress, pain, and even while dying. This may be related to the beneficial effects of purr vibration frequencies on bone repair, or it may be a self-soothing mechanism. A cat that is simultaneously purring and breathing at an elevated rate will have the respiratory frequency change masked by the purr, giving the impression that "it's purring, so it must be fine."

What the Coat Tells You

This section needs to be long. Coat changes carry the highest information density of all chronic pain signals, and are simultaneously the most commonly misattributed.

Feline self-grooming is a whole-body movement. Licking the mid-to-lower back requires significant spinal flexion. Licking the ventral abdomen and inner hind legs requires full hip abduction. Licking the tail base requires lumbosacral rotation. Each region corresponds to a set of joint range-of-motion demands. When osteoarthritis limits the range of motion of a particular set of joints, the cat abandons the grooming zone that makes the highest demands on those joints.

The coat quality distribution on an elderly cat's body therefore becomes a map. The head and chest are clean, because these areas can be reached with the front paws and mouth without bending. The scapular region is slightly worse. The mid-back begins to show roughness and mild matting. The lumbosacral area and tail base become oily and tangled. The inner hind legs and ventral abdomen are worst.

The boundary line of coat deterioration is the contour line where pain limits range of motion. This line migrates upward as joint degeneration progresses. If six months ago the boundary was at the lumbar region and now it has moved up to the mid-back, it means spinal flexion capacity has further deteriorated.

The vast majority of owners who notice this phenomenon interpret it as "the cat has gotten lazy about grooming" or "could it be a skin condition." The first attribution shuts down any further investigation. The second at least gets the cat to a vet, but after a dermatological exam turns up no primary skin pathology, many veterinarians stop there too, without asking "why has it stopped grooming this area."

Here there is something rarely discussed. Coat changes do not only indicate the presence of pain. They can also indicate the rate of pain progression. If you take a set of standardized full-body photos of your cat once a month (one from each side, one from above, one from below, with lighting as consistent as possible) and arrange the photos chronologically, the expansion speed and direction of coat deterioration zones become trackable. Three months ago only the tail base area had mild matting, and now the lumbar back is also starting to get oily. That rate of change is, by itself, useful information for the veterinarian. Far more useful than walking into the clinic and saying "its coat hasn't been great lately."

There is another situation that is easy to confuse with pain-related grooming reduction: psychogenic over-grooming. Cats driven by anxiety or compulsive behavior will excessively lick specific areas, licking the fur off and sometimes creating skin ulcers. In these cats, the coat problem presents as focal alopecia zones with clear boundaries, and the distribution of alopecia has nothing to do with joint range of motion. It usually occurs in the areas easiest for the cat to reach (inner forelimbs, ventral midline). The distribution pattern of pain-related grooming reduction is the exact opposite: the hardest-to-reach areas have the worst coat. The two patterns on the map are complementary. If both are present simultaneously, with a cat whose forelegs are licked bald and whose back is matted, the probability of concurrent anxiety and pain is high.

Jumping

The early signal is an increase in the crouch time before takeoff. A healthy cat's jump is almost instantaneous from crouch to launch. A cat with joint pain pauses an extra beat in the crouched position. This "extra beat" is roughly a fraction of a second. Without deliberately watching for it, it goes completely unnoticed.

A signal with even more diagnostic value than the pre-launch pause is the landing. A healthy cat lands with all four limbs touching down nearly simultaneously, and the whole movement is quiet. A cat with joint pain lands front limbs first, hind limbs slightly delayed, and at the moment of touchdown the body has a very brief freeze, under one second, before resuming normal movement. This freeze is a reflexive muscle contraction triggered by the landing impact transmitting through the forelimbs to the shoulder joints and spine. The audible difference on a hard floor: a healthy cat landing makes one soft thud, a cat with joint pain makes two, with a discernible time gap between them.

If you have more than one cat in your home, one young and one old, find a surface they both jump onto (a windowsill, a tabletop) and listen carefully to the difference in landing sounds. It will be very obvious.

Changes in jumping route appear later than changes in landing sound. A cat that used to jump directly from the floor to the windowsill and now detours via a chair is already showing a relatively late-stage signal. Long before that, the extra fraction-of-a-second pause on landing was already there.

The Litter Box

A cat with joint pain shortens its time crouching in the litter box, reduces or eliminates digging and covering, shifts urination position from the center of the box to the edge, and may eventually urinate on the floor outside the box. The driving force behind all of these changes is the same: crouching and stepping over things hurts.

Under this topic there is a practical detail that often gets skipped. High-sided litter boxes and enclosed litter boxes are extremely unfriendly to elderly cats with joint pain. Stepping over the box wall requires single-hind-limb support plus hip flexion, which is a high-load movement for a deteriorating hip and stifle. Many litter boxes have entry heights between 15 and 20 centimeters. For an elderly cat with hip pain, those 15 centimeters are the entire reason it chooses to urinate on the floor. Switching to a shallow tray with an entry height below 8 centimeters sometimes resolves the out-of-box elimination problem the same day. This is not behavior modification. This is removing a physical barrier.

Joint pain

A cat with joint pain urinates at normal frequency and volume, and the out-of-box location it chooses is typically right next to the litter box, because it walked to the box and then could not or would not step over.

FLUTD / Cystitis

A cat with cystitis urinates more frequently, in smaller volumes, possibly with hematuria, and the locations it chooses outside the box are usually random, anywhere at all.

"Urine next to the box" and "urine on the living room couch" point in completely different directions.

After Frunevetmab

Chronic analgesia in cats was long constrained by species-level hepatic metabolism characteristics. Cats have low UGT enzyme activity. Many NSAIDs that dogs tolerate chronically carry accumulation risks in cats. Long-term use of meloxicam has always been controversial. Gabapentin has limited efficacy for osteoarthritis pain. In 2021 frunevetmab was approved. Anti-NGF monoclonal antibody, subcutaneous injection once monthly, does not go through the hepatic glucuronidation pathway, safety profile suitable for long-term administration. It filled a gap that had existed for a long time.

The reason this drug occupies space in this article is not the pharmacology. It is what happens in cats after treatment.

Many cats that received frunevetmab therapy prompted owner reports that went beyond "it can move again." The cat started grooming the fur on its back again. Started jumping onto laps again when someone sat down. Started sitting at the windowsill again, watching the outside. Recovery of mobility can be explained by the joints no longer hurting. Recovery of social willingness and environmental interest cannot.

Long-term pain, through sustained HPA axis activation and altered central monoamine neurotransmitter function, puts a cat into a state of overall reduced vitality: sluggish, withdrawn, indifferent to stimulation. This is not a personality change. It is a functional suppression at the neurochemical level. Analgesia lifts the suppression, and the cat "from years ago" reappears.

Regarding this recovery process, there is a reaction on the owner's end that is worth recording. When the cat becomes active and affectionate again after treatment, the owner's first response is usually not happiness. It is guilt. The realization that "its quietness before was not personality, not age, it was pain the whole time" hits harder than the joy of seeing the cat jump onto the refrigerator again. A sentence that appears repeatedly when owners share their frunevetmab treatment experience on social media: "I didn't know it had been in pain for so long."

Veterinary Visit Rates

The annual veterinary visit rate for cats is significantly lower than for dogs. Transport stress is high, the waiting room environment is unfriendly to cats, and "cats don't need regular checkups" is a widespread belief among cat owners. The Cat Friendly Clinic certification system has attempted to improve the waiting room experience, with limited reach.

The consequence of this does not need much elaboration. If the cat never comes through the door, no professional assessment can take place. For most household cats, the owner is all there is for pain recognition.

Behavioral Problems

A cat suddenly biting may have had its pain site pressed, triggering a protective attack. Increased aggression toward cohabiting cats may stem from chronic stress lowering social tolerance thresholds. Excessive licking of a specific area may indicate deep-tissue pain at that site, with the cat attempting self-relief through endorphin release via licking. Decreased tolerance for petting may be the result of central sensitization, where the dorsal horn, after prolonged nociceptive input, lowers its excitability threshold so that previously non-painful touch-pressure starts being processed as pain signals.

Starting behavioral modification before pain has been ruled out means stacking training pressure onto an animal that is already enduring pain. This does not need discussion. It needs to stop.

One trap that is particularly easy to fall into is interpreting out-of-box elimination as "revenge." "It's peeing outside the box because it's angry." Cats do not have the concept of revenge. A cat's cognitive architecture does not support the causal reasoning of "you did something I didn't like, so I will use a behavior you don't like to punish you." Out-of-box elimination has only two categories of cause: physiological (pain, urinary tract disease, nerve damage) and environmental (litter box location feels unsafe, litter substrate is not accepted, box is too dirty, box walls are too high to get into). "Retaliatory urination" is not among them. The subsequent responses this misattribution leads to (punishment, isolation, abandonment) all point in the wrong direction.

Baseline

Approximate daily food and water intake. Number and volume of urine clumps in the litter box. Frequency and route of jumping onto elevated surfaces. Frequency and coverage area of self-grooming, with particular attention to the back half of the body. Resting respiratory rate. Response speed to the sound of a can opening or a feather wand. Number of times per day the cat voluntarily rubs against a person or jumps onto a lap.

No spreadsheet needed. A rough sense of the normal range for each dimension is enough. A single dimension shifting: take note. Two or more shifting simultaneously: book a vet appointment.

Taking three standardized full-body photos of your cat each month is worth repeating. It is more useful than any single observation technique.