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Why is my cat hissing at his sister after she was outside for weeks?

Updated On September 23rd, 2025

Pet's info: Cat | American Shorthair | Female | spayed | 2 years and 5 months old

Why is my male cat hissing at his sister? She's been gone for two weeks cause she ran outside, but we caught her yesterday. They grew up together.

2 Answers

Most Helpful Answer

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Answered By Jennifer Summerfield, DVM CPDT-KA

Veterinarian, Certified Dog Trainer

Published on July 20th, 2016

Cats will often do this if they have been separated for a period of time, especially if one cat looks or smells different - your female cat may have strange smells on her from her time outside. Most of the time, this reaction is mild and the cats will get along again after a day or two. If there is any serious fighting or if his aggressive behavior towards her does not seem to be improving, then you may need to separate them and gradually reintroduce them to each other - feel free to ask for additional help on this if needed :)

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16Pet Parents found this answer helpful

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    Answered By David Elbeze, DVM, MRCVS

    Veterinarian

    Published on

    She probably came back with smells from other animals, maybe other cats, and that is probably what makes him hiss at her. Once the smell will be gone, he will stop, it might take a couple days.

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    15Pet Parents found this answer helpful

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