Non-recognition aggression is so preventable!

Only one cat going to the vet.

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. This is called non-recognition aggression. His friend does not recognize him. His friend is frightened, and attacks to defend himself when this “stranger” 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.

A man prevents non-recognition aggession by blocking the cats view of each other with a towel.
Preventing non-recognition aggression.

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 8

  1. 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

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  2. Our house is open plan. How can I successfully separate our 2 brothers as one has started attacking his brother and sniffs him alot

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      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!

  3. 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.

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      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.

  4. 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.

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      You need to reintroduce them following the steps in

      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.

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