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Q&A: Why Is My Male Cat Suddenly Aggressive Toward My Other Cat?

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Dr. Mark is a veterinarian. He works with dogs, cats, exotics, and livestock.

Feline non-recognition aggression can be frightening to witness, but there are steps you can take to help.

Feline non-recognition aggression can be frightening to witness, but there are steps you can take to help.

How Do I Stop My Cats From Fighting After a Brief Separation?

"Our two male cats always got along very well but recently we took one cat for a 30-minute car ride and after returning they got into a bad fight. The cat now hisses and searches for the other cat to attack him. What caused this?" —Nathaniel

Feline Non-Recognition Aggression

This problem is common among families that bring one cat to see the vet and leave the other cat home. It is actually called Feline Non-Recognition Aggression (1) and is something we do not see with other pets.

I hope by now that your cats have stopped fighting, because in some cases this only goes on for a day or two (while the cat that went out for a car ride smells differently).

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How to Reduce This Type of Aggression

The first thing to try is to rub a washcloth on the aggressive cat's face and then rub that on the cat that went for a ride. In some cases, this can work immediately.

If the aggression is still going on after trying the washcloth method, you can purchase a pheromone from Amazon called Feliway, which has been proven to reduce this problem (2), but it may take up to four weeks to work.


  1. Dodman, Feline Non-Recognition Aggression, Veterinary Practice News, 2011.
  2. DePorter, T. L., Bledsoe, D. L., Beck, A., & Ollivier, E. (2019). Evaluation of the efficacy of an appeasing pheromone diffuser product vs placebo for management of feline aggression in multi-cat households: a pilot study. Journal of feline medicine and surgery, 21(4), 293–305.

This article is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from your veterinarian. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.

© 2022 Dr Mark

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