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I have two cats that have always got along well together. I have never had to stop my cat from bulling my other cat, and never experienced any kind of conflict between them. In fact, I’d have said they were best friends. So you can imagine my surprise when one cat is hissing at my other cat after a vet visit. What is going on? Why are my cats suddenly fighting after vet visits?
As it turns out, this is an extremely common form of cat aggression known as non-recognition aggression. Your cat doesn’t recognize your other cat when it returns home and thinks it is an imposter. This is because of unfamiliar smells your cat has picked up on their time away from home.
In this article, I explain how this is possible – how can your two cats seemingly have forgotten each other after a short time apart? And more importantly, I share tried and tested tips on how to stop cat aggression after a vet visit. Or at least, to speed up the re-introduction process.
What is Feline Non-Recognition Aggression?
The reason for your cat hissing at your other cat after the vet – or after any time spent away from home for that matter – is because of feline non-recognition aggression. This is where your cat fails to recognize your other cat after they return home. They see your cat as an intruder that is infringing upon their territory!
Cats hate new people and animals being in their space. Think about it, when you first brought your second cat home, did your old cat dislike it? Cat depression after a new kitten is introduced into the family is extremely common. I bet you worked hard to make your cat stop hissing at the new kitten. And slowly, your two cats became best friends.
However, failure for your cat to recognize your other cat on their return home essentially resets this initial dynamic. It is as if you are bringing a new kitten into the home all over again. Your cat is scared of the “new” family member. Both your cats need to re-learn to trust and like each other again before they can live together comfortably.
What Causes Aggression After Vet Visits?
So, feline non-recognition aggression is to blame for your cat’s hissing and other aggressive behaviors. But hold up – how can a cat completely forget its best friend after such a short time apart?
In truth, this type of aggression is not fully understood, but it is all to do with changes in your cat’s scent while they are away. Cats rely heavily on scent for communication. Their sense of smell is 14 times as strong as ours! Therefore, it is thought that cats identify other cats not through what they look like, but rather through how they smell.
Cats that live in the same household will share the same family scent. It is this scent around your home that helps cats feel calm and why moving to a new environment is so stressful. But when your cat returns from the vet, it might not smell like it did before it left. Below are some examples of how your cat’s scent has changed:
- Hormonal Changes: The hormones of sick cats will be all over the place as their bodies try to recover from illness. Because cats have such a strong sense of smell, your other cat might be able to sense these changes. In other words, your cat smells sick. This smell overlays the family scent, causing your other cat to not recognize them.
- Stress Pheromones: Most cats hate going to the vet. I have to deal with my cat biting and attacking me every time I put her in the cat carrier! This stressful experience will cause your cat to release stress pheromones from their anal sacs. Once home, your other cat will be able to smell these stress pheromones and assume that danger must be nearby. This can cause them to act aggressively.
- Vet Smells: There is also the chance that your returning cat smells of the vet. For example, they might smell of alcohol, medication, cleaning products, or disinfectant used. This will cause your other cat to not recognize your cat. Plus, your cat probably has negative associations with these scents, further worsening their aggressive behavior.
- Other Animals & People: Your cat will also have picked up smells that belong to other animals and people on their trip to the vet’s office. This could be the vet themselves or from the other pets waiting to be seen. Your other cat can detect these smells and get confused about who your cat is when they come home.
How to Prevent Aggression After a Vet Visit?
If you are dealing with feline non-recognition aggression, know that your cats will recognize each other over time. The lingering smells from the vet’s office will gradually get lost and your cats will be friends again. So don’t panic that this new dynamic will last forever – it won’t.
However, aggression after a vet visit is not easy to deal with even if it is only temporary. You’re going to need to take your cats to the vet regularly for check-ups and more so as they age and develop more serious medical conditions. You don’t want to be dealing with hissing and aggression after every vet visit!
Therefore, it is a good idea to prevent your cats from acting aggressively in the first place. Here are just some things that can really help with this.
1. Schedule Vet Visits Together
This is a simple but effective fix. If both your cats go to the vet together, they will both have been handled by the same staff and in the waiting room with the same animals. They’re being exposed to the same cleaning products, disinfectants, and so on.
This means that your cats will be able to understand these scents when they come home. They’ll still be able to recognize each other for who they are under the lingering vet smells. As a result, they’ll be much less likely to attack each other or any other animals and people in your home. Scheduling routine veterinary visits together can work wonders!
2. Keep Sick Cats Separate
One of the reasons your cat might not recognize your other cat is because sick cats smell differently. Therefore, it might be a good idea to keep your sick cat in a separate room on their return home. If your kitty is recovering from an illness, the last thing they will want is to be attacked! As they recover, their hormones and “sick smell” will fade so they are recognizable once more.
Besides, removing your sick cat initially will give them time to groom. Through grooming, they’ll remove any lingering smells from the vets, such as alcohol and disinfectants. It also gives your sick cat a chance to calm down from the stressful vet visit, which is another big plus.
3. Spread the “Family Scent”
All cats that live in one household share the same “family scent”. This is what your cats use to know who is a friend and who is a foe. You can help spread the family scent back onto your cat that has been away so they are recognizable to your cat that has stayed at home.
To do this, take a towel and gently rub it on the cheeks of your cat who has stayed at home. Cats produce a lot of pheromones from glands in their cheeks. Rubbing here will transfer these pheromones and the family scent onto the towel. You can then rub this towel all over the cat who has been to the vet to transfer the scent onto them.
4. Make a New Communal Scent
Some owners find making a new communal scent and spreading this on both of their cats to be more effective. The cats will still smell alike which will help them to identify each other as family. Just be sure that whatever scent you choose is (1) safe for cats, (2) pleasant for cats, and (3) strong smelling.
One good example would be to use juice from a can of tuna. We all know that cats love the smell and taste of tuna, so it is pleasant. Tuna is also safe for cats and won’t do them any harm. And tuna has to be one of the smelliest fish there are. Simply pour a little tuna juice on your hands and rub it on both cats to transfer the scent onto them.
Using this method will also encourage cats to self-groom. Doing so will help to remove any lingering smells your cat has picked up from the vet. It will also help to renew the family scent and potentially even lead to your two cats grooming each other.
5. Brush & Bathe Your Cat
You can also help remove the unfamiliar veterinary scents from your cat yourself by brushing and bathing your cat after their trip to the veterinarian. Most cats will enjoy being brushed and it can even help them calm down after their stressful vet visit. Bathing is a less popular pastime for cats, but if you’re up for the challenge it can help remove foreign smells.
6. Be Patient with the Re-Introduction
Most importantly, you need to be patient with your cats’ re-introduction. When bringing your cat back from the vet, be very aware that your other cat may be aggressive. Watch for the first signs of confrontation to help avoid fights from breaking out.
For example, cats arch their backs when scared and defensive. They’ll also have puffy tails, flattened ears, and wide eyes. This will usually be the case for the cat returning to the household. The cat that is left behind will instead show attacking signs. This includes staring with small constricted pupils and facing the other cat as if ready to pounce.
If you notice any of these early warning signs, you should separate your cats for a little while. Moreover, if your scared cat hides, leave them to it. Dragging your cat out of hiding could make them more fearful, which in turn leads to more aggressive behaviors. Slowly re-introduce your cats at a pace that works for them.
What to Do if My Cats Are Fighting?
Despite trying your hardest at preventing non-recognition aggression from arising, sometimes it still does. Here are some tips on keeping things under control:
- Never let your cats fight it out! This could result in injury and tension. Instead, try and stop the fight by clapping your hands or spraying the attacking cat with a water gun. This could cause the cats the stop fighting long enough for your to separate them.
- Heard the attacking cat (usually the one left at home) into a separate room and give them time to calm down. Try to do this without picking your cat up as it could result in them scratching and hurting you. If you need to pick the cat up, pick them up in a towel.
- Let your other cat (the one that has just returned from the vet) retreat and hide. This is an instinctive response to stressful situations and soothing your cat too early can make the situation worse. Let them come to you and offer them comfort and affection when they want it, never before.
- Once both cats have calmed down, you can reintroduce them. It is usually a good idea to do this gradually. For example, you might want to feed them on separate sides of a screen door. Once they seem relaxed like this, you can slowly let them spend more time together.
MY FINAL THOUGHTS
Your cat hissing at your other cat after a vet visit is extremely common. This is known as feline non-recognition aggression, and it all boils down to cats and their powerful sense of smell. Your returning cat will smell different and be perceived as a risk.
However, hissing can soon lead to attacking and a full-blown catfight! Therefore, it is important to try and prevent non-recognition aggression before it happens. Also, watch for the early warning signs that a fight could be brewing and separate your cats as soon as possible.
I had one cat spayed a couple days ago and was prepared for the possibility of the one being home to become aggressive or upset. Well my cat at home did do the normal hissing and taunting so I kept them apart best I could. Now it’s my newly spayed cat that is doing the attacking. They are now completely separate. When the newly spayed cat even sees a glance of the other cat she will run full force claws out and attack her. I’ve never seen this before… what do I do?!
I hope you managed to sort this out, and get them to start first tolerating each other, and then getting along again. I had to bring one of my cats into the vet to have dental cleaning and one tooth extracted. I have three cats, they have lived together since being kittens, born in 2017. The cat was only gone a couple of hours. That was over a week ago, today is the first day that I have a little bit of hope that the aggressive cat that was left at home is going to accept her again. I’ve even had to get medication for the cat that was left at home, she has been so nasty and combative. Gabapentin. And also, because it was dental surgery, I have to make sure that the patient doesn’t eat any of the dry food. I cannot believe that it lasted so long, and that it is still going on, today is day 10. I have had to split the entire house into two or three separate zones, and also make sure that I am spending time with all of them, because jealousy will start otherwise. It has really been a nightmare, I don’t know what I’m going to do the next time one needs to go to the vet for a procedure.
Good luck with yours.
I’d take them all to the vet, regardless. Only way to get them all to smell alike,
I have never had this problem even though I’ve had various cats over the years. I have a problem now after one vet visit and not the other. The situation has been going on for a month now and shows no signs of stopping. I have tried a suggestions on the internet – now going to try both cats in the same room with harnesses and leads on but not able to reach each other.
This was SOOO HELPFUL!! thank you so much! My tortoiseshell cat had two teeth extracted four days ago and has been so aggressive towards my Siamese boy. They normally have a love/hate relationship but she never fights him even if he jumps on her back. Now she is the aggressor and we didn’t know what to do. I wish the vet would have warned us that this could happen and we could have tried some of these ideas sooner and prevented the fights from happening. I hope they eventually forgive each other and move on.
I agree. It would be nice if the vet had warned us. We are having this problem right now.
Our vet actually DID warn me about this, but I shrugged it off…. Oops! Sure enough, even though we were only at the vet for an hour, just getting vaccinations, senior check up and blood work, when we returned our other younger cat was hostile. Ironically, I took her to the vet the day before and our older cat couldn’t have cared less when she got home! But thanks for the suggestions, I will definitely try them all!
We are having this same problem after taking 1 of our Ragdolls to the Vet for normal exam 6 days ago. This has never happened before and I have had cats for over 20 years. So bizarre. They used to get along pretty good before. The aggressive cat will walk by the treated one and hiss and smell her behind and then growl and sometimes swat. I hope this goes back to normal soon. We had them separated for a few days but now they are out. Not sure what to do at this point…
I have 2 cats, brother & sister, same age. The girl cat is the only one that shows aggression toward her brother if he, she or BOTH of them go to the vet. I take them in separate crates because they’re pretty big now & the girl cat has a bowel movement in her crate once the exam is completed. He’s never behaved aggressively towards her even if she’s the only one that’s gone to the vet. It’s always her who hisses & growls at him if he gets close. I feel so badly for him because he’s sad & confused at her behavior towards him. I tried separating them, but neither will eat because they usually eat side by side. But after they’re done eating she wants nothing to do with him. HELP!!
I’ve always had multiple cat households. Old kitties passing to the rainbow bridge and new cats moving in. Luckily, for over 40 years, it been a smooth transition. I have noticed that when my cats get older, 14 and up, that sometimes the other cats start bullying. Nothing extreme but it bothers me because I’m trying to keep a calm house for everyone, including the elder cats. Does anyone have any suggestions (other than Pheromone spray) on how they’ve kept the cats from bullying the elders? Thank you.
Both of my cats went to the vet today for a routine checkup and my girl cat has been hissing at my boy since they got back. They both smell different I know but she seems to be really struggling with this non-recognition even though they left together and came home together. I will try wiping down their fur tonight and if that doesn’t work I’ll try the tuna tomorrow!
I have two 15 year old cats- they are siblings and the girl cat came home from the vet and her brother is hissing at her and I wiped her down and it doesn’t seem to be helping. She is trying to snuggle her brother but he is not having it. I don’t know what to do.
I have 2 cats brother and sister they have been hand reared and have spend every second of their time together you couldn’t separate them were the one was the other one was. She had a seizure around 3 weeks ago and they were separated for 3 days but were completely fine her brother was really concerned when he seen her not well. But my Tom cat got hit by a car last week and has had to have surgery for a broken femur it has been the other way for her with him. he was gone for a week in between vets and home so they have been separated on and off for the last week. since he has come home she now won’t come in the house only to eat and on the rare occasion she does come in and sees him in his crate she is hissing and growling at him then goes back out. He has to be inactive and kept in a crate for 8 weeks for his leg to have any chance of healing but I’m really concerned the longer they spend apart they will never have the close bond they had before and how can I try and coax her to come in from outside as she just stands by the door meowing like she’s scared to come in.
I’m searching this topic after the fact. I had no idea and it’s challenging. 2 sisters from the same litter have been together for over 5 years with no problems. 1 had to go to the vet and I thought about bringing the other, but didn’t. We were gone a little over 3 hours. The visit was stressful enough for her and me, so I was completely taken off guard by the 1 who was left at home. I never heard her hiss a day in her life, at her sister or at me. I couldn’t understand how one seemed to forget the other. It’s a little over 24 hours now, but the one who stayed home is still somewhat uneasy. After the fact, the vet did tell me that the medications, numerous handlers, and the pet dander of other patients can play a role. Feliway was suggested. All I know, is that I’ll never leave the house without the other again.
Same here. Big problem. I took my cat to the vets yesterday because she had a urine infection. Came home and my other cat who is her sister attacked her. I stayed up all night with them and they still the same today. Tried putting old scent on her but hasn’t worked so far.
How are things now? Are they back to their old selves? If so.. how long did it take?
Same is happening to me, 2 cats, ages 7 and 11. Took the younger one to the vet yesterday and the elder one has been hissing, ears back, and growling since we got home, we were only gone 3 hours and it didn’t happen the last time, there were a lot of dogs in the waiting area this time though.
Its worrying as the elder one had a bladder blockage 6 months ago and gets cystitis when stressed, luckily I have gabapentin for him but it hasn’t helped so far!
Just reading all the messages has really reassured me though so thank you, I thought he had gone senile or something, hopefully, this will sort itself out soon as I too did not sleep properly last night, and neither will tolerate being shut in a room so having to manage it by providing food and litter trays in separate rooms and staying with them constantly, it’s a nightmare!
I have two 6 year old cats that are brothers. They have always been close with each other. 3 days ago, I took them to the vet together for their yearly check up/shots. They were hissing and growling at the vet, which they have never done before or at home. Since returning home, they are still doing it only to each other. I don’t know what to think. They should both smell the same.
My sibling, female siamese cats spent almost 2 weeks hissing, growling and fighting after one returned home from the vet after a dental extraction. It was a living hell. I just couldn’t leave them alone. They got over it thankfully. I used feli friends and pet remedy sprays and plug ins. Next vet visit for their annual vaccinations they went together in separate carriers and I actually put them back into the opposite carrier coming home to ensure a good mix of smells. Sadly it didn’t make any difference. The same cat was terrified and hissing at her sister. It took a couple of days for them to settle again. Then tonight I had to take the same one who’d had the dental extraction to the vet. I’ve got the same hissing and fear from the other one yet again. I’ve sprayed pet remedy, turned on the diffuser, rubbed them both around the jowls with remedy wipes and still it’s happening. I’m currently lying on the bed with the scared one with a cat calming gadget playing soothing music. I’m feeling so stressed It’s making me feel sick. I hate this happening every time no matter what I try,
I have to take my cat regularly to the oncologist as it is a chronic condition. It seems like the aggression is lasting longer each time I come home. They are brothers that I have had since kittens. When I separate the aggressor, he sprays the room I keep him in which he never had done this before however I’ve never had to close him in a room before. How do I stop the spraying and why is the aggression getting worse as the vet visits go on?