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Why is my cat aggressive after vet? Reintroduce in small apt?
Updated on September 23rd, 2025
Pet's info: Cat | American Shorthair | Female | spayed | 8 lbs
Our cat had 3 teeth extracted. Now our other cat has feline non recognition aggression and is hissing and growling at her. We live in a small 1 BR apt so we can't keep them in separate rooms. Cat 1 also had very bad breath because of her tooth problems, so her smell has changed significantly. I'm afraid they'll never get back to their former relationship where they slept together, bathed one another, etc. is there anything we can do? I'm afraid to leave them tomorrow when we go to work!
4 Answers
Most Helpful Answer
Answered By Anna M., DVM
Veterinarian
Published on July 9th, 2017
The most important thing right now is to not allow them to fight or have negative interactions. As long as they can be kept separate while they both settle down, they will probably do ok - but if they continue hissing and growing, and worse yet if it escalates into a fight, that could permanently damage their relationship.
I would absolutely keep them separate until they seem to be relaxing. I understand that'll be challenging in a 1 BR living space - but if possible, you could put 1 in the bathroom with her own litterbox & food, and then have them switch places tomorrow so they can get reacquainted with each other's smells. If that's not possible, you may need to crate them both while you work on their reintroduction. Perhaps you could borrow dog kennels so they can each have their own living space while they're confined.
I know this isn't an easy answer - but the most important immediate intervention is to do what you need to do, to keep them from fighting while the stress levels come down!
Finally, adding a pheromone diffuser such as Feliway Multicat may help promote a calming atmosphere.
I hope this helps!
2Pet Parents found this answer helpfulRelated Answers from Veterinarians
Answered By Dr. Melanie, BVSc MS
Veterinarian
Published on January 12th, 2017
The reason why is that Gizmo may smell differently after being separated. You can see this behavior when animals come back from the vet, as they smell differently. I would separate the cats, and slowly reintroduce them to each other. Take the cat who is aggressive, and put her in her own room with her own food, water, and litter box. Keep the door closed, and for a few days, feed them both treats on other side of door so they associate each other's smell with a good experience. Then let the other cat in the aggressive cat's room while the aggressive cat is in a cat carrier. They can smell each other, but not be in contact. If either becomes upset or show signs of aggression, remove the second cat from the room, and try again later. Praise them when they interact appropriately. When they are interacting well with each other through the carrier, you can let the aggressive cat out of her room, and see how she interacts with the other cat. Praise them when they interact appropriately, and separate them with any sign of aggression or upset. I would get a cat tree with lots of shelves to give the cats vertical space to get away from each other. I would keep the cat in her room when you go out until they are comfortable with each other.
1Pet Parents found this answer helpful
Answered By Dr. Melanie, BVSc MS
Veterinarian
Published on May 7th, 2020
Thank you for contacting Petco Pet Education Center, formerly Petcoach with your question. Likely because one of your cats was at the vet, he smells differently so 2B views him as a stranger. leading to the aggression. I would separate the cats, and slowly reintroduce them to each other. Take 2B, and put him in his own room with his own food, water, and litter box. Keep the door closed, and for a few days, feed them both treats on other side of door so they associate each other's smell with a good experience. Then let the other cat in the aggressive cat's room while the aggressive cat is in a cat carrier. They can smell each other, but not be in contact. If either becomes upset or show signs of aggression, remove the second cat from the room, and try again later. Praise them when they interact appropriately. When they are interacting well with each other through the carrier, you can let the aggressive cat out of his room, and see how he interacts with the other cat. Praise them when they interact appropriately, and separate them with any sign of aggression or upset. I would get a cat tree with lots of shelves to give the cats vertical space to get away from each other. I would keep the cat in his room when you go out until they are comfortable with each other. I hope this helps!
1Pet Parents found this answer helpful
Answered By Dr. Melanie, BVSc MS
Veterinarian
Published on April 21st, 2018
Great question! When a cat spends some time at the vet, they can return home smelling differently and that can lead to the aggression from the other cat in the home. I can give you a method to help get them along again. I would separate the cats, and slowly reintroduce them to each other. Take the cat who is aggressive, and put him in his own room with hs]us own food, water, and litter box. Keep the door closed, and for a few days, feed them both treats on other side of door so they associate each other's smell with a good experience. Then let the other cat in the aggressive cat's room while the aggressive cat is in a cat carrier. They can smell each other, but not be in contact. If either becomes upset or show signs of aggression, remove the second cat from the room, and try again later. Praise them when they interact appropriately. When they are interacting well with each other through the carrier, you can let the aggressive cat out of his room, and see how he interacts with the other cat. Praise them when they interact appropriately, and separate them with any sign of aggression or upset. I would get a cat tree with lots of shelves to give the cats vertical space to get away from each other. I would keep the cat in his room when you go out until they are comfortable with each other. Best of luck, I hope this helps!
1Pet Parents found this answer helpful