What is non-recognition aggression?
People recognize each other by sight. Cats rely more on smell. Each group of cats has a group-scent. If one cat goes somewhere and returns smelling as if he is from another group, he very well may be attacked when he comes home. He may also be attacked if he smells afraid or sick. This is called non-recognition aggression. His friend does not recognize him. Or he does, and is afraid of his fear or illness. His friend is frightened, and attacks to defend himself when this “stranger” or “unsafe cat” approaches. And, yes, it can even happen between cats that have been life-long friends.
How does this happen?
It often happens when one cat goes to the veterinarian. Just as a toddler may be frightened when his big brother walks in the door wearing a scary mask, a cat may be afraid of the scary smell of the veterinarian’s office. His friend smells like a stranger, but is coming right in the door! Right into his home! Well-meaning strangers do not do that, so this is frightening. The cat feels the need to defend himself.
Non-recognition aggression can also happen if that cat had gone to another house. And in the case of indoor cats, if one cat gets outside and then is found and returned, his housemate may attack him. In all of these cases, the cat is not recognized due to the scary smell he has acquired.
How do you prevent it?
If one cat has been out of the home for any reason, please keep him separated from the other cats for a couple of hours. This allows him to lose the smell of the foreign place and start smelling like home again. If the returning cat is sick, it is best to keep him separated until he is feeling better. Cats can smell differently when they are ill. And when you do reunite these friends, monitor them closely. Have a large towel handy to separate them should there be any tension. If a cat is staring, tense, or lashing his tail, separate them. Don’t wait for non-recognition aggression to occur before doing so. And do not punish either cat, or show fear or anger. Be matter-of-fact.
What if there was an attack?
If there was any non-recognition aggression, the cats will have to be kept separated and slowly reintroduced. You can learn about introductions in my blog about this. And you may want to schedule a consultation to ensure it goes smoothy. Undoing incorrect introductions is a long, tedious process.
Patience Fisher owns Patience for Cats LLC, a cat behavior business based in Pittsburgh, PA. She is Associate Certified by the International Association of Animal Behavior Consultants. She holds a Bachelor’s in Biology, a Diploma of Feline Behavior Science Technology, and is a certified veterinary assistant. Check out her humorous YouTube video at her Patience for Cats channel. Visit her on Facebook at Patience for Cats.
Comments 14
Hello there
I have 6 kittens (littermates)
I have 4 male kittens they will be going to get neutered
should I take all 4 to get fixed to avoid non recognition aggression ? I am worried due to recently taking 2 females and the males want nothing to do with them
thank you in advance any advice you can pass forward
Author
Either way, be prepared to slowly re-introduce them after they recover from surgery. My blog on cat intros might help with that. https://patienceforcats.com/introducing-two-cats/ Since they know your house, you’d be on the step of letting them see each other through toddler gates.
Our house is open plan. How can I successfully separate our 2 brothers as one has started attacking his brother and sniffs him alot
Author
You would need to close a cat in a bedroom, and have the cats take turns at large. Be sure they don’t see each other when you swap out!
I recently brought in a cat tree and it was unfortunately infested with fleas (didnt cross our minds to check) and of course my cats were rolling around on it and sleeping in it so i had to bathe them separately. Long since the shower (which was a few days ago) my cat has started hissing aggressively to my other cat (who are both females) but it seems that the other cat still recognizes my cat, my cat has started hitting the other cat. Any suggestions? And maybe something i should mention is that they share one litter box.
Author
I would separate them, or at the very least arrange resources such as litter boxes (you need at least two), food, water, toys, scratch post, etc. so that the cats need not cross paths to access theirs. For instance, you can have resources on each floor of a two-story house. Then you should book a consultation so we can come up with a customized reintroduction. Here is the link to my intake from. https://form.jotform.com/onebarnowl/cat-client-history
I took my male cat to get neutered and female started attacking him. They have been separated for a week now but when I try to reintroduce she starts attacking. Not sure what to do or if it’s just a matter of time. We swap rooms and do feedings at the door.
Author
You need to reintroduce them following the steps in https://patienceforcats.com/introducing-two-cats/
I do NOT recommend feedings at the door! That can make things worse, as the cat is forced to eat next to a cat that upsets him. Most people find a consultation useful, so I can help you take specific steps based on your cats’ body language during the first incremental exposure. All too often people make things worse doing the reintroduction on their own. You can request a consultation using the link to my intake form. https://form.jotform.com/onebarnowl/cat-client-history
I had this issue with my male cat when he had a urinary issue and was in the hospital for a few days. My cats are 3 years old and from the same litter and bonded. I was shocked when I brought male cat home female starting attacking him. Comments above worked for me,.. keeping them separated but I used baby gate so they could see and smell one another. I also bathed my sick cat with baby shampoo. I would also put them in same room and sit between them and give them both anttention/affection and play with them to reassure niether was a threat. It took about 3 weeks to get them back together.
Author
I’m glad you were able to reintroduce your cats successfully! But in general, bathing the cat is not recommended. That will create a strange smell as well, and might even frighten a cat. Smelling fear can cause an attack. As can smelling illness. And shampooing won’t get rid of those smells since they originate from within. I’m glad the shampooing didn’t cause any troubles for your cats. And I’m glad you took your time with the re-intro — well done!
One of my cats has had multiple surgeries, most recent being 48hrs ago. Each time we do a vet visit, we take both cats with us. Obviously the healthy one doesn’t stay at the vet, but does the trip there, gets out in the office and trip home. We thought this would help with the smells and up to now it always has.
It hasn’t worked this time, and I now have one poorly cat desperate for her friend, and another cat who is hissing and hiding from her.
I can’t work out what went wrong this time, but any ideas on fixing it?
They seem to have taken up residence in different bedrooms, but are both rather miserable
Author
You need to reintroduce them. I recommend scheduling a consultation with me so you have a customized plan.
Vet smells aren’t the only cause of so-called non-recognition aggression. There is also the smell of sickness or fear, and visual signs of both as well.
The vet came to my house to give all 3 their shots. Now my 2 male cats are yowling and trying to kill each other. The female is hissing at her littermate but not the other. I’m keeping them separate but they never left the house and shouldn’t smell different. What could it be?
Author
It could be that they saw and/or smelled fear. Once they are calm, you should re-introduce them per my blog https://patienceforcats.com/introducing-two-cats/