I took my cat to the vet for 30 minutes. When I got her back home, her brother started to hiss on her and he looks aggressive. she tried to touch his nose but he still doesn't like it.

  • Should I leave them alone? Can they resolve the problem?
  • What is causing that problem? do you have an idea? Is it maybe the perfume of the vet? or he doesn't recognise that smell?
  • Did not work at all. Took both cats to vet. The non-treated cat is hiding in the family room and hisses when he sees his sister. Even treats do not work. I am at a loss.
    – Ruth
    Aug 20, 2021 at 21:38
  • @Ruth I think you meant to leave your comment under the current answer by Rebecca, not under the question. Aug 22, 2021 at 23:36
  • Hello @Ruth, Hope your cats are ok. Don't worry about it. Let your cats get some steam out. Leave them alone, do not interfere in their business. Sooner or later they will get along again. After their sterilization surgies. It took the female cat, one week to get back to normal. She was so mad at her brother. IT's hard and annoying, but remain calm and let them be. They will come to terms. Don't call them "BAD" or shout at them. Let them be
    – Hani Gotc
    Aug 23, 2021 at 8:55

1 Answer 1


Why does this happen?

This is fairly common and is termed Non-Recognition Aggression, cats rely on scent to recognize each other. Her visit to the hospital has changed her scent to the point where her brother can no longer recognize. A few theories behind it are:

  • The cat expressed his/her anal glands or is emitting pheromones associated with stress.
  • The cat took home scents of other animals who were previously at the clinic

What to do?

It is a good idea to keep them separated in the meantime for each others protection. A few things that can help:

  1. Giving blankets with each others scent to opposite cats (i.e brothers blanket goes with sister and vice-versa)
  2. Feliway Friends

After 24 hours try to gradually re-introduce them, either by opening the door a crack for them to sniff or to have a gate in between. It does self-resolve after some time you just need to make sure the conflict is over before putting them in the same room.

How can I prevent this?

Next time, if possible, bring both cats to the hospital - they won't lose sight of each other.

  • 2
    well I tried to let little mizzy out. Mr grumpy smelled her nose and all went well. SOO HAPPY
    – Hani Gotc
    Sep 25, 2018 at 17:07
  • 1
    For future references I applied the first suggestion: Giving blankets with each others scent to opposite cats (i.e brothers blanket goes with sister and vice-versa) Thank you
    – Hani Gotc
    Sep 26, 2018 at 22:08
  • I am trying to better understand this answer. If cat A no longer recognizes cat B because cat B no longer smells like cat B, how does giving cat A a blanket with cat B's scent help? (Or did I misunderstand the recommendation?) Aug 22, 2021 at 23:35
  • @RockPaperLz-MaskitorCasket This is *symmetric . When you rub Kitty B with Kitty A blanket. Then Kitty A will think. Holly mother of Cats. Kitty B has the same smell as I R. So it will know that they belong together. Or at least belong to the same pack and vice versa. Freaking Cats, I know
    – Hani Gotc
    Aug 25, 2021 at 11:35
  • 1
    @HaniGotc Thanks for getting it though my dense non-kitty brain. As an experiment, I tried removing the middleman, and so instead of using a blanket, I just rubbed the kitties together real fast. All I wound up with a flaming ball of kitties. Lesson learned. Aug 26, 2021 at 1:25

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