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.
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.