Why does my cat hiss at her sister after she returned home?

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 :)

Cats exhibit this behavior sometimes when one leaves the house. Most of the time it’s more growling and hissing and running then anything else. Most cats will get over this quickly. Supervise them so that they don’t hurt each other and make sure one does not bully the other. If you have something they really like it such as canned cat food, you could try feeding both cats the food or treats close to each other and talking sweetly and petting both. I hope this helps and best of luck!

This can happen after a stay at the veterinary clinic. It should pass in a few days as Stella loses the scent of the clinic. You can try a pheromone product, such as Feliway spray or plug in diffuser, to decrease any anxiety.

It's possible the stress of your being gone caused the behavior change. I would give Hippy a few days to rest, relax, and make sure she can get to her food, litter, places to hide, etc without being bothered and see if that helps. Sometimes, pain or underlying illness can also cause a cat to suddenly lash out and hiss or swat at other cats, so if the behavior continues or you see visible signs of illness, a vet visit to rule out health issues is best.

Did Pernell go to the vet recently or leave the house for a period of time? When cats go to the vet or leave the house for a period of time (such as going to a kennel), they can come back smelling differently and that would cause the existing cat to view the returning cat as a stranger. Then that would lead to aggression. Or it could be that Gattino isn't feeling well. If he was in pain that would causing him to react aggressively to Pernell. I'd recommend a check up with the vet for Pernell to make sure everything is ok. I hope this helps!

Hi and thanks for posting on Petco Pet Education Center, formerly Petcoach! If Milo has stayed for the week with your brother or sisters cats whom Milo has never met before while you were away, it possible those cats did not like Milo very much or became stressed with a new cat in their home. If Milo use to get along with your brother/sister's cat before, perhaps you leaving triggered the stress and aggression of the other cats. Cats do not do well with change and can really become stressed when their owner's habits or environment changes suddenly. It is best is Milo is kept at distance from your brother and sister's cats as much as possible for several weeks and then try slowly reintroducing them with a few short introduction sessions under supervision. Feliway pheromone spray diffusers around the house can work on easing tension. I hope this helps and best of luck to you and Milo!

Gizmo can likely smell the vets off of DeEtta, she will think this is very odd and be unsure. This should only be a temporary situation and should resolve with time. You could try using a feliway diffuser to help settle them.