Feline Non-Recognition Aggression

Non-recognition aggression is exclusive to felines and only adds to the mysterious persona cats have taken on.

One term used to describe and assess feline personality is “equability,” referring to mood stability. Some cats scoring high on this scale are extremely stable and highly unlikely to fly off the handle. Others, at the opposite end of the scale, are mercurial and may become enraged almost literally at the drop of a hat.

The latter type of cat is most likely to be the aggressor in what is descriptively termed “non-recognition aggression.” This type of aggression is something that all veterinarians should know about because it usually entails aggression of one cat to another after a visit to a veterinarian’s office. A typical scenario is as follows:

Cats A & B, though not necessarily mutually bonded, cohabit peacefully until the fateful day. Cat A is taken to the veterinarian’s office for some procedure, often one entailing the use of heavy sedation or anesthesia. On being brought home and let out of his carrier, Cat A is immediately and savagely attacked by Cat B, almost as if Cat B does not recognize his long-term housemate.

The attacks by the resident non-equable cat on the cat returning home from the veterinarian’s office can be quite savage and may lead to ongoing feuding between the cats, with subsequent development of territoriality and fearfulness propagating the on-going conflict.

In one case, a husband tried to break up an attack by one of his cats on the other, who had just returned from the veterinarian’s office having been de-matted and given a bath under heavy sedation or anesthesia. Unfortunately for the man, the resident cat’s non-recognition aggression redirected toward him and he was forced to lock himself in the bathroom for hours before the cat’s ire subsided.

Needless to say, I advised the owner that these two cats, who were, at that time, engaged in ongoing hostilities, should be kept separate for quite some time. They were to be reintroduced to each other gradually over a period of days or weeks at a rate determined by their reaction to each other.

Digging Deeper

When I inquired about these two cats’ history together, the owner remembered that there had been a similar incident in the past after the victim cat adopted full affective defense mode—hair on end, pupils dilated, hissing and claws unsheathed—and discharged its anal glands on seeing a wild animal outside. Immediately following discharge of its anal glands, the other cat attacked it and feuding ensued for several days.

It should have been clear at that time that because of the aggressor’s non-equable personality, the stage was set for another aggressive incident whenever something untoward or unexpected occurred.

Anal gland discharge  struck me as a distinct possibility as the cause for non-recognition aggression. My thinking was as follows:

Cat goes to vet and has to be restrained, becomes scared, expresses its anal glands and, when it comes home, literally smells of fear, which alarms the other cat and promotes an attack.

It turns out, however, that anal-gland discharge may not be the trigger, at least not in every case, because this owner took it upon herself to have the victim cat’s anal sacs extirpated following our meandering discussion of the subject. The anal sacectomy had been a simple procedure, she assured me after the fact, taking only a few minutes and causing minimal discomfort.

Naturally, when the cat came home after the procedure it was kept separate from the other cat for a while before the two were allowed to mingle. If anal gland discharge was the trigger, that should have been that, a permanent fix. But it was not so. Sometime later, the victim cat was taken to the vet again and a false sense of security by the owners caused them to allow the cats to see each other soon after the victim cat’s return. A vicious fight ensued, followed by separation and gradual reintroduction, as usual.

I have heard all sorts of suggestions about what may be the trigger for non-recognition aggression. It may be something unusual about the look of the returning cat. Perhaps it has not recovered properly from anesthesia and is walking differently or just looks strange. Perhaps it is something about the smell of the cat, if not anal glands, perhaps the smell of iodine, alcohol or vitamin B (which seems to pervade most veterinary establishments).

I’m not sure exactly what the true cause is and it may even be different in each case. I do know that people have tried myriad measures to prevent non-recognition aggression, such as always bringing both cats to the vet’s office or rubbing them down with the same cloth before reintroducing them so that they smell alike. None of these of works consistently.

The only thing vets can do is appreciate that non-recognition does sometimes occur and seems to involve the non-equable personality of one of the cats. If this type of aggression occurs even once it is likely to occur again, so steps must be taken to guard against it.

What to Do?

It does not seem that there is anything that can be done before or during a veterinary visit but afterwards it is necessary to separate susceptible cats for however long it takes for them to get back to square one in their relationship. Maybe it takes only a few hours or days for both cats to realize that there is nothing to fear and get back to their regular feeding, playing and self-grooming schedule.

Once reaching this stage, when the sight of each other through a 1-inch crack in a partially closed door does not trigger an aggressive response from either cat, they can be allowed greater access to each other under strictly controlled and closely monitored conditions. This can be achieved by holding one or the other cat in a blanket for the reintroduction, applying a harness to the aggressor or confining him in a cat carrier until it is clear that peace reigns.

Non-recognition aggression in cats is an odd entity that does not seem to occur in dogs. I believe it is unique to the cat world. What it is about their personalities or sensory perception that leads to this phenomenon is unclear, adding to the usual perception of cats as being mysterious, unfathomable and, in general, something of an enigma. 

An author and researcher, Dr. Dodman is a professor at Cummings School of Veterinary Medicine at Tufts University and is founder of Tufts’ Animal Behavior Clinic.


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4 thoughts on “Feline Non-Recognition Aggression

  1. We just gave our new cats (brothers from the same litter, 4 months old) a bath for the first time, bathing Cat A first. We noticed Cat B getting aggressive and hissing at cat A but assumed he just didn’t want to Cat A to get him wet. We bathed Cat B, who showed no signs of aggression toward us after getting out of the bath, and let them both roam our apartment to dry off at their leisure. However, we started noticing continued aggression of Cat B to Cat A. This seemed odd after reading your post because they should both smell the same now since we used the same soap on both. I’m not sure what to do about it since every trick I’ve seen has been related to getting them to smell the same.

    1. Sorry you went though that, I go through it myself . I hope by now things are back to normal. After the bath your still suppose to seperate the cats . I also would use strictly fragrance free cat shampoo. Then once separated after the bath it can take days or weeks for their normal scent to come back. If you open the door a crack and there’s still aggression then they are not ready to be together again. I didn’t give my stay at home cat a bath just the one that went to the vet. Then waited for his scent to be reestablished which for me took about a week. I kept him in a room and the day after the bath, I gave him his favorite blanket to help him along to get his scent back along with him grooming himself.. it worked, but was stressful and hate to think I may go through it again. It is no fun..heartbreaking

  2. I have 2 cats:Rosie and Lucy. They were best friends, cuddling, playing, and grooming each other. 2 nights ago Rosie accidentally got locked outside. I found her hunkered undered a parked car in my parking lot. I brought her back in and Lucy started hissing. I bathed Rosie 3 times and Lucy is still hissing. Lucy will hard stare are Rosie and look on edge. If they get close, Lucy hisses. I rubbed them botb with the same cloth, rubbed juice from wet food can on them hoping that would make them sniff and make nice. No luck. I locked Rosie in my room all day yesterday and Left Lucy in the living room. Then I switched then. I locked Lucy in my room last night and left Rosie in the living room. I reintroduced this morning and Lucy still hissed. I’ve had Rosie for 8 years and Lucy for 2. Lucy was never this mean, not even when I first adopted and brought her home. Then, they hissed for about a day and then they were best buddies. This is so sad.


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