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How To Deal With Non-recognition Aggression In Cats

Nov 8, 2017 · Updated Nov 8, 2017 · ·
  1. Anne
    How To Deal With Non-recognition Aggression In Cats
    It's a story we often hear on the cat forums. Two cats that used to get along suddenly turn into enemies. The trigger? One of the cats had spent some time outside the home. Upon its return, the other cat sees him or her as a threatening stranger. The term for this kind of behavior is "non-recognition aggression". If you have more than one cat, you could be facing this situation too someday.

    Why does non-recognition aggression even happen?

    I have two cats, Shadow (10 years old) and Sylvester (5 years old). Shadow has a gum disease and I took her to the vet last Friday. I brought her back in the house and put her down on the ground and Sylvester attacked her, ripped off her bandage, her collar and had tuffs of her fur under his claws.
    From the cat behavior forum

    Why are we seeing this type of behavior in cats? Why would a healthy cat turn on the sick cat and attack? After all, they used to be good friends before.

    The answer is that they probably don't even recognize the cat at that very moment.

    This sounds strange to us as we rely on sight for recognizing other people. For cats, however, the more relevant sense is scent. The cat returning from the vet doesn't smell like the cat they knew before. This cat is covered with strange scents to the point that he or she becomes unrecognizable. The resident cat therefore reaches a conclusion: Someone swapped his former friend with a stinky alien.

    Cat behavior experts call this "Non-recognition syndrome". Some believe that it's not only the strange smells that were picked up by the cat while outside the home. The new smell may also be the result of the cat's own fear. Having spent the day in unfamiliar surroundings, the returning cat could very well be very stressed and fearful. He or she may still be in pain or under the influence of anesthesia drugs, and this is something other cats could pick up on, whether through smell or body language. Those cues - invisible to us - could also trigger an aggressive response.

    For some cats, the smells from a veterinary clinic may just be too frightening in their own right. Even if they recognize the returning cat, they may still lash out in response to the smells that remind them of their own scary experience at the clinic.

    Is non-recognition aggression triggered only by vet visits?

    Non-recognition aggression can be seen in any situation where the cats were separated. A vet visit is the most usual scenario because that's a common occasion where one cat leaves home and returns hours or days later. The same type of behavior can also happen following a visit to the groomer but most cats don't require such visits, making this a rare trigger.

    When an indoor-only cat manages to get outside for a few hours or even days, he or she may experience the wrath of non-recognition aggression upon returning home. The longer the time spent outside, the more likely he is to pick up new and unfamiliar scents that can trigger the response in other household cats.

    How to deal with non-recognition aggression in cats?

    Whenever one of your cats is separated from the others, you should keep this type of aggressive behavior in mind. There are things you can do to try and prevent an onset of non-recognition aggression, but if all else fails, you need to be prepared to deal with the situation.

    Deal with stress early on.

    Stress makes cats more prone to aggression in general. Just like in humans, elevated levels of stress can put a cat "on edge". When a stressed-out cat is confronted with the unfamiliar scents on the returning cat, he or she is more likely to lash out.
    Read more about stress in cats and the strategies you can use to reduce stress.

    Use care when bringing a cat back home from the vet

    Don't just waltz into your home and put the cat down on the floor. Instead, keep the returning cat in a separate room for a few hours to make sure he or she is feeling better and is more relaxed. If Kitty underwent anesthesia, make sure the effects have passed and he or she is ready to face the world again. Keeping the cat in a separate room gives him or her time to groom and regain some of the familiar scents of your home.

    Before allowing the cats to meet, grab a blanket or a cloth that your cats regularly come in contact with and rub it on the returning cat. Your aim is to re-apply familiar scents to cover up the "vet stink".

    Have the cats meet each other in a gradual way. Open the door to the separate room to an extent that allows mutual sniffing but allows you to cut the encounter short by shutting the door if needed.

    Remain calm while the cats meet each other and avoid staring directly at either cat. At the same time, do keep an eye on them and be prepared to step in.

    What to do if one of the cats becomes aggressive

    A certain amount of hostility is normal in this situation. If one of the cats hisses and then moves on, that's ok. However, if either cat lashes out, you'll have to break up the cat fight by placing some kind of barrier between the cats. Be careful! If one of the cats is very upset he or she can quickly re-direct that aggression towards you. Always keep your hands away from a scared or aggressive cat.

    Keep calm and avoid shouting or reprimanding any of the cats, regardless of their reactions. They're not misbehaving. They're just being cats, acting on sensory input that you don't have access to.

    If the cats are very hostile towards each other, you may need to separate them for a few days until both sides calm down and then introduce them again, as if they've never met before. Use our guide: How to successfully introduce cats and follow through. Don't rush the process to give the cats the best chance at becoming friends once again.

    Have you ever experienced non-recognition aggression with any of your cats? Share your story in a comment below and let us know what happened. As always, if you need more help, share your experience in our cat behavior forum where members can support you in your efforts to deal with non-recognition aggression.

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  1. Michael Brown
    We have two cats, a male (6 years old) and female (5 years old). They adore each other. The male recently got sick and made several trips to the vets. When he returned from his last visit, the female was very aggressive towards him and attacked. She had never done that before. It was distressing to say the least because the male was weak. We separated them. With her, I knew the aggression was due to his new smell. But, he had started to hiss back at her because of the attack and had looked distressed. We worried that the dynamic between them had changed as he, the male, was putting out fearful, defensive signals. Cats are hyper sensitive to body language. The vets had advised us to keep the cats separated for 2 weeks to a month. My instincts told me otherwise based on knowing our two cats. I wanted to re-introduce them quickly so as to not develop a rift. I'm not saying this is the way to do it for everybody, I just had a hunch it might work for us. That night, when the female was very tired and sleeping, I brought the male in. Then, I let him roam around. She saw him. Before there was a face to face, I grabbed a laser so as to distract them both. They both focused on the laser and chased it. Then, as we finished, I quickly fed them their favorite snack out of my hand. They sat side by side focusing on the food. Finally, that night, they slept in their usual chair together. There were the odd hisses but they were basically back to normal. As the days passed, more and more their normal relationship resumed. The male was still hesitant of her but as time wore on, that changed. For us the key was in avoiding the stares and head on confrontations yet letting them get familiar by being in the same environment together. I did it through distraction and by petting both of them to exchange each others' smells. They were in the same environment but were not focusing on one another. I hope this helps anyone else going through the same situation.
      Furballsmom purraised this.
  2. caracoveney
    This happened with two of my cats last year. I had to keep the younger in a cattery on its own for over a week whilst I 'cat-proofed' my garden, as he was getting ill by going into a neighbouring field, where there was a lot of ash. (The other two cats didn't wander into the field so were not at risk.)

    On his return, it was horrendous between my two. They had never been the best of friends but had been amiable enough, but the older cat treated the younger like a mortal enemy on his return! Snarling, spitting, swiping - it was awful for a couple of days I went onto a cat forum and a lady there suggested that I use a cloth on both cats, and then rub the 'mixed' scent onto each of them, then wipe it along things in the house and garden at 'cat height'. It was like magic. The effect was immediate. I have used this method ever since if one of the cats has had to stay at the vet for any reason.
      blozano purraised this.
  3. debl58
    We are going through this right now. Wish I had known this was a “thing” before taking the one cat to vet. I would have just taken both of them and avoided this nastiness. But at least I know now and hope the one that was left at home “wakes” up and realizes Loco is her baby brother she’s known for 5 yrs. great article, great advice.
      dustydiamond1 purraised this.
  4. kitty chew
    I'm having this problem also. Just brought my cat Smokey home from a traumatic 3 day stay at the vet with a virus, to have his sister and best buddie, hiss at him. She is being horrible towards him, doesn't even want to stay in the house with him. She has been hiding in the cat run.
  5. terischlem
    Still dealing with this non recognition aggression, since one of our cats got a lion cut on Monday. He had alot of mats & some were starting to pelt. Andy was at the Vet’s office for 8 hours getting shaved down in short increments. Now his sibling sister is a bully toward him. She hisses & appears like she may lunge after Andy. We have tried separating them. We bought a Feliway diffuser & a Feliway spray bottle, to spritz around tables & under beds where they hang out. Andy’s sister(from the same litter), is still angry at Andy.

    We will give it one more week, but if Zoey doesn’t stop her hissing & bad behavior, we are thinking about giving her up. It is sooooo sad to witness this aggression. They were bosom buddies before. Not they are enemies. Andy is just Andy...& Zoey now sees him as a threat. Never saw this coming. Never heard of such a thing until we started researching it.

    We love both cats, but refuse to live with one cat being mean to her brother. It’s like we brought home an unwelcome adopted cat... only it’s not. It’s her own brother that she grew up with. They are 4yrs old now. Very sad. ☹️
  6. Nikki_P

    I posted this question on the article regarding gradually introducing new cats, but thought it would be appropriate to post on this thread, too, as it concerns feline non-recognition aggression. Thanks!

    We recently brought home our kitty, Mi-Go, from an extended stay at the vet. To our surprise, our other kitty, Binx, became extremely aggressive towards Mi-Go. We have since learned that this is called feline non-recognition regression and should have taken steps to reintroduce the cats slowly, much like is suggested in the article above. Unfortunately, it's been three weeks since Sir Mi-Go has been back home and we're just now finding this all out.

    To further complicate matters, Mi-Go is an extremely emotional cat and would come undone if we cloistered him away for a few weeks. No exaggeration, this cat is extremely sensitive and is prone to depression over the littlest thing (eg: we didn't "invite" him to sit with us on the couch, or we dared to shut our bedroom door).

    Binx, however, would probably do fine if we shut her in the master bedroom for a few days. We've actually done that very thing in the past few weeks when neither my partner nor I have been home to referee between the cats, and she seems very at ease in there by herself (of course, taking care to give her loves, treats, and attention when we return).

    My question is, do you think this will work to sequester the aggressive/threatened cat, Binx, or will it cause more harm to keep her from roaming freely through her house? Is the only way for this to successfully work to have Mi-Go, the returning cat, be the one that's tucked away?

    Also to note: We really love our cats and give them all a lot of affection and play time, and try to use positive reinforcement as much as possible. Also, we've tried Feliway, but it hasn't seemed to help in this situation.

    Any advice appreciated!
  7. yelpot
    Firts I have to thank you for this article. I wish I had this Saturday . My Milo went to the groomer. When we arrived home my heart broke. Him and pepa we're so close. I feel so bad
  8. BayouBlessings
    I wish I'd known about this! Yesterday I shaved my Maine Coon and now my other cat, who just adores him, hates him! I'm a groomer, so it's not like I took him somewhere else, but as soon as I finished his haircut, the other one screamed at him. They got into a terrible fight. I've separated them and will follow the guidelines of introducing a new cat. Thanks for the article!
  9. Kez
    We have 17 month old brother sister siblings who we keep probably 97% of the time locked up inside. We have a large 4 bedroom house with a two and a half car garage all well equipped with several litter boxes, scratching posts, toys and plenty of free shelving for them to climb up on. They are only ever outside if we are home (they don't wander far) and we never leave them out at night either.
    We are very interactive with our cats, playing with them all the time, chat away to them - they quite often chat back (cute) Maisie especially likes to stay close but everything is on her terms when it comes to picking her up for cuddles where as Stuart loves cuddles and play fighting with my Husband. He is a bit of an explorer and will go for a wander to the paddocks behind us when allowed out.
    Stuart is a much larger cat than his sister Maisie and has on the odd occasion thought it would be a good idea to bail her up, much to her protest. We never hear Stuart letting out the blood curdling cat scream but Maisie will.
    What we are confused about is that Stuart, when confronted by any of the neighbour's cats, he either runs for his life or becomes quite submissive - much like Maisie when Stuart has a go at her. BUT. Maisie, as tiny as she is, has no problem having a go at any of the neighbourhood cats should she feel threatened, even coming to Stuart's aid if need be.
    Why do the roles get reversed and why does Stuart just randomly do this to Maisie? Any help or advise would be much appreciated as getting rid of either of them is not an option and if we can "nip" this in the bud now, would be great.
    Cheers from NZ
    1. Michael Brown
      Context. In your house they have defined roles. Cats operate on a hierarchy--there's almost always a dominant cat--in this case Stuart. That doesn't necessarily mean aggressive. Outside, their roles/behaviors might be different. Not sure why Stuart does that to Maise, he may be reading her body language and a bit of fear. Not sure how to help--but I did see a show in which an animal behaviorist came in to a house in a similar situation and retrained the submissive cat how to act so as to not be targeted.
  10. Threecozycats
    We think this could be happening with our two cats who are littermates. They got along just fine until about 1.5 years ago when the female started growling/hissing at the male every time he walked in The room and/or attacking him just for walking by. Want to say this started after a vet visit for the male being sick but cannot remember as it was so long ago. This behavior has progressively gotten worse despite feliway diffusers and calming collars. It’s gotten to the point where they cannot be in the same room together and she pretty much has isolated herself to our bedroom. Now the male is exhibiting anxiety and anxious behaviors and the fighting has just gotten worse. Is there any way to manage this now that it has been going on for so long? Feel like we have tried everything under the sun. Also both got a clean bill of health from the vet so we have ruled out any medical issues.
    1. Michael Brown
      This is heartbreaking. I'm not sure if there's a good answer. I really think vets have to be more cognizant of this and advise all of their customers about these dangers. It's probably best to bring them in together. Here's my guess--based on our experience. Initially, the hissing occurred after a vet visit. This would have been due to the different smell--and cats recognize each other through smell. But that would have worn off after a couple of days. I think after the initial hissing or attack, the attacked cat becomes fearful and releases whatever fear hormones there are--the other cat picks up on it and reacts aggressively--then there's a cycle of behavior that gets established. The key may lie in the immediate return from the vets and separating them until the smells are back to normal. In your case, now it seems like there is a behavioral pattern that needs to be addressed. Have you tried a cat behaviorist specialist to come in and see if he/she can fix it?
  11. BangkokKittens
    Great article. I wish I had seen this before I tried to reintroduce a post surgery mother to her four kittens (see link below)

    Rescuing Feral Kitten In Bangkok

    I was so happy to reunite them that I just crudely dumped Mom back in the room with the kittens and it was a disaster. At first they were extremely hostile and stressed out. So, I pulled her out and tried several more times. I think the core issue was the she smelled and acted differently, but I think I made it worse by just dropping her into "their space"

    Following that I gradually reintroduced her several times, with a bit less hostility but not much satisfaction. I always made sure they were all fed first and if I fed them together made sure the food was spread out and abundant.

    Importantly, I later just opened the door to the room they were in and introduced her downstairs, so they could meet in a neutral territory.

    Over 10 days or so, they seemed to gradually get more comfortable with each other and finally seemed to actually like each other. Oddly, I didn't see them redevelop a maternal bond until yesterday when she broke them out of the house and led them on a madcap escapade.

    Now that I have trapped them and have them all bad in the house, they are finally a family again!

  12. furrypurry
    This has happened several times with my two Himalayans, even when they both go to the vet at the same time! They are littermates and have been together since birth. Jaspurr gets hissy and it can last for a week. Purrcy never hisses or acts aggressive, even if Jaspurr goes to the vet without him and comes home smelling weird. It stresses me out drastically because we usually have a very peaceful household. The one thing I have found that works is similar to rubbing the cats down with a familiar blanket, etc. I read about this and I was thrilled that it worked. BEFORE going to the vet, take a pair of clean socks and rub one cat down well with one sock, then rub the other cat down with the other sock. Be sure to rub around the face and the scent glands. Put both the socks in a zip lock bag together. Upon returning home, before you let them have contact, rub both cats down with BOTH socks, melding their scents. The time I did this we had ONE half-hearted hiss from Jaspurr and all was well after that.
  13. dhruska211
    Thank you for the article. I have an aggressive cat the only one I have 26-month-old kittens that iPhone a one-year-old seven is the aggressive 17 and 21.
    And Neighbor asked me if I would take the now seven-year-old and she was not socialized she had two cats of her own she kept this one confined.
    She is free to mingle with the other cats but I don’t keep any of them locked up I never did I have tried everything but you still mean. To make matters worse I didn’t know that she was the one eating all of the dry cat food..... I recently change diet completely she will have nothing to do with raw food. But she does need food so I gave her the dry.
    Furthermore she has attacked to pet sitters. Growls and hisses at my son and she has bit me. I have to go to the hospital for that one it was very deep I was folding laundry at the time. I have tried everything oh and she went after my neighbors one year-old grandson. At this point I think there’s something seriously wrong with this cat She can be very loving one on one but is soon as the other cats come around she is just miserable. Any suggestions because all my other cats are nice - But they don’t put up with her either
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