Problems with other Cats in house when one returns from vet

We have two cats that are brother and sister that we have had since they were small kittens. They've always gotten along and snuggled to sleep together and are the sweetest cats. Theyve never hissed, bitten anyone or growled. The male cat had a urinary problem and we took him to the vet today, upon returning the female keeps hissing and growling at him. At first when I scolded her she would stop and run away, then a few minutes later she hit flipped out and tried to bite me and continuously hissed and growled at me while I was separating her from her brother. The male is just confused and wants to be around her and is standing outside the door to the room she is in waiting for her. She is growlimg thru the door. What do we do and why is this happening? We have been home for hours now and she smelled the carrier and was fine. She didn't even get 15 feet from him before this started and won't get closer unless she's hissing, growlimg, or attacking him. Any suggestions or thoughts would be greatly appreciated.

My malé cat would do that when my female came home from the vet. It is because the cat smells like the vet office. If your cat takes baths you can wash him and the other cat will stop. Otherwise in a day or so the vet smell will go away and they'll be back to normal.

I'm really eager to share with you and see how things go with you and your girl.  I started another thread without seeing this one because I am having a similar issue.  The cat in question is doing it whenever any of mine go in and unfortunately it is going on 6 days now.  She has recovered faster before and I'm concerned.

Mine goes absolutely like she has a screw loose when this happens.  She can be fine and then if she sees or smells something threatening she goes totally bonkers -hissing, growling, swatting, running and even sometimes looking around like she is hearing voices in her head.  It is very sad, and also heart breaking and stressful.

Maybe we can at least share what we are trying and perhaps it will help to know we have company.  It makes me rather nuts in kind, you?

This is very normal.  They smell different when they come back from the vet especially because it is a stressful thing.  Cats know each other by scent.  I have this issue every time my girls go to the vet...even when they go together.  They are litter mates also.  It can take up to a few days for things to calm down.  She may also be reacting to him being sick.

I will put a dab of vanilla (like I use for baking) on the back of each of their necks to help them start smelling alike again.  

I would keep them separated while the girl calms down.  If you had a towel or blanket in the carrier the boy cat laid on while on the way to and from the vet you can put that in the room with her so she can check the scent out off it.  Also if she has a blanket some say rubbing your boy cat with that may help transfer her scent to him.  I've not had to try these things myself.  We have some good articles on introducing cats that may have things that will help you smooth things out too.

One thing you can do before the next vet visit is rub each cat down with a sock, paying close attention to the heavy scent areas like around the face and the base of the tail.  Then, when the vet kitty comes home rub it down with the same sock so you are putting "home" smells back on.  Again, paying attention to the base of the tail and face....all over though.  When I remember to do this I really think it helps.

I agree with MoochNNoodles, you need to change the way your cats smell, since smell is their most used and most powerful sense. Cats are territorial and mark their territory with their scent by rubbing against everything, so you can see why a change in the way one of them smells is going to throw off the other cats. You can use vanilla or talcum powder to make all of the cats smell the same. I use talcum powder. Be careful if you go the talcum powder route. You want to rub the powder into your hands, then pet your cats. Don't apply directly to your cats since the powder can get in their sinuses. This has worked 100% of the time for me, and it's usually a very quick fix.

Also, remember that you have to do this with all of the cats, not just the one who went to the vet. You're trying to make them all smell identical, not just cover up the vet smell with another foreign smell.