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Warning Signs When Introducing Cats & Guide To Do It Successfully 

Bringing a new cat into your home can be a nerve-wracking experience for your current kitty and any other pets you have in your home. I just went though this experience, so I have advice on introducing a new feline to your house of pets and signs that the meet-and-greet isn't going as smoothly as you'd hoped.

Sally Jones

Last Updated: December 14, 2023 | 10 min read

Angry cat hisses to another cat

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Most resident cats don’t welcome a new kitty into their home with open paws. The presence of a new feline usually forces cats to go into their natural territorial mode. This can occur even with laid-back cats and those who have been previously socialized with other cats. Unfortunately, it’s just the way our finicky furballs are wired.

Your current cat, or cats in my case, will most likely see a new feline sister or brother as a threat. But you have some ways to make this huge life change an easier transition for all involved. The best things to keep in mind during this process are to take it slow, be patient, and try not to get discouraged. Cats aren’t naturally social with fellow felines, so it can take weeks and even months for them to get used to each other.

I have important tips for you to follow on everything from finding a compatible kitty to specific ways to help the introduction process go as smoothly as possible. I also share some of the warning signs when introducing cats that you may need to slow things down.

First Things First: Finding An Ideal Match

A personality match can be key when choosing a second kitty. It’s impossible to predict if the two will eventually become best buddies, but considering some of the following factors can at least help them get along better. The Animal Humane Society says that adult cats typically accept a kitten more easily than another adult cat. And American Humane says that gender, breed, size, or other qualities usually aren’t major factors to consider.

  • Try to find a cat with a similar personality and disposition to that of your resident cat.
  • If your current kitty is very laid-back, shy, or finicky about interactions, a highly energetic and boisterous adult cat may not be a good fit.
  • On the other hand, if your current cat is a wild one, a quiet, low-energy, or skittish cat may be overwhelmed in your home.

In my case, I rescued a 6-week-old kitten, who my daughter’s friend found in an outdoor trash can and was covered in mud. How could I not take him in? Monk is an extremely sociable kitten and wants to be with his new feline sisters most of the time, so it was hard to keep them separate for so long. He’s also quite rambunctious, so I had to take the introduction process very slowly. It can be a frustrating time, but it’s worth it in the long run.

Before The Introduction

I have two resident sibling cats, Lola and Bammy, and a dog, Tiny, so I had to ensure that I was prepared to bring a new cat (especially a young kitten home). What are the basics you need to know?

  • If your new feline friend is a stray, you’ll need to get him thoroughly checked out by your vet to protect your resident cat’s health. This involves a couple of regular tests. I did this with Monk since he was a stray. I got the all-clear from my vet the same day, so Monk was ready to come to his new home.
  • If you adopt your new kitty from a shelter, he’s likely already been tested for feline diseases and checked for fleas, worms, and other health issues.
  • Make sure you have everything on hand, your house set up, and a clean bill of health before bringing your newcomer home.

What You’ll Need To Purchase

It’s important to have all of this gear for your new kitty because you’ll need to keep her separated for the first phase.

  • Food and water bowls
  • Another litterbox (you should have the same number of litterboxes as cats)
  • A kitty bed
  • Interactive toys (a lot in my case for a playful kitten)

You’ll also need a tall pet safety gate, two shorter baby gates (stacked on top of each other), or a mesh screen door. This aims to keep your new kitty physically separated but allows them to see each other. This will help the introduction process go more smoothly and is a good way to keep cats separated when you have to leave them alone. I chose the QWR Reinforced Cat Screen Door, and it worked well.

Prepare A Separate Room

Select a small bedroom or bathroom with an inch or two of space under the door for your newcomer. Set up the litterbox, food and water bowls, toys, and bed. The space under the door will serve an important purpose with initial introductions.

Being in an enclosed area of your home will help your new kitty warm up to his new environment without becoming too overwhelmed. And it keeps your cats separate so you can control the introduction process. I got Monk all set up in my spare bedroom, which was ideal for him to have enough room to run around.

How To Introduce Two Cats: A Step-By-Step Guide

An orange cat sitting on a table with a Tabby hissing up at him from the floor.
If introduced too quickly, cats may take much longer to warm up to one other and may never get along.

Since cats are highly territorial and solitary creatures who don’t adjust well to changes in their environment, it’s extremely important to plan out first impressions. Following the steps below is key. There’s no set-in-stone amount of time you should spend on each step.

In general, many experts recommend not moving on to visual contact until at least five days. In reality, a cat introduction timeline boils down to how things are going. Just keep in mind, don’t move on to the next step until each cat seems fairly comfortable with the situation. See below for positive signs and warning signs to look out for to gauge how your cats are handling each step of the process.

How to introduce cats infographic.

1: Bring Your New Kitty Home

Before walking into your home with your newcomer, make sure someone else keeps your current kitty occupied, so he doesn’t see your new fuzzy bundle of joy. Take your new kitty to the room you’ve set up; this will be his temporary pad for several days. Having space under the door is key because animals use scent as a crucial way to first explore each other. This way the cats can hear and smell but can’t see or touch each other.

2: Feed Them On Opposite Sides Of The Door

At mealtimes, place each cat’s bowl near their respective side of the door that separates them. Feed them at the same time. This helps them associate coming close to each other with a pleasant experience. Give both special treats near the door to enhance this positive association. You can begin to move the bowls closer to the door after each meal. You’ll continue this ritual throughout the entire introduction phase.

3: Exchange Scents

Once your newcomer seems comfortable (this could be anywhere from a few hours to a few days), it’s time to kick up the scent introductions by switching places. This method allows each cat to further sniff out the other’s scent.

  • Remove your newcomer from her pad and take her to a location where your current kitty can’t see her (no sightings are extremely important at this stage).
  • Let your resident catwalk into the pad and shut the door.
  • Then allow your new cat to explore your house.
  • Repeat this swap several times per day.

An excellent additional way to exchange scents is by rubbing your cats with the same towel or blanket separately to intermingle their scents. Then leave the towel with each cat for a while so they can investigate their intermixed scents. I used this method for several days.

During this time, you may also want to play with the cats near the door. You can encourage them to paw at a small ball or mouse toy under the door. If things go well, they could even bat the toy back and forth. This gets them to associate a positive, fun experience with each other.

4: Make Visual Contact

The next step is to open the door and place a tall gate or mesh screen in the doorway. This way, they still don’t have full access but can see and have some contact with each other. Once you’ve secured your gate, have someone place each cat on the floor several feet from the gate at the same time. When they notice each other, give them a treat and praise to make the experience less stressful.

Expert Tip: Many cat behaviorists recommend starting the visual introduction by first draping a blanket or sheet over the gate. This method gives you more control over the degree of visual access, so you can gradually let the cats get used to the sight of each other. Anxious cats may benefit from this extra layer of taking things slow.

Continue feeding, treating, and playing with your cats near the gate, gradually moving bowls and toys closer. I used a cat wand toy and a laser pointer to engage them in some interactive play. My resident kitties were fascinated watching Monk play in his room.

Positive Signs When Introducing Cats

If your cats are exhibiting the following signs in the visual introduction phase, it’s likely time to take the next big step to the full meet-and-greet. However, many cats will only reach the point of eating near each other, so it’s fine to move on as long as there aren’t any warning signs.

  • Eating food and treats and playing with a toy close to the other cat.
  • Ignoring each other but seeming content on their side of the gate.
  • Touching noses through the gate.
  • Rubbing their bodies against the gate.
  • Pawing each other playfully through the gate.

5: Meet Fully (When They’re Ready)

Once your cats seem comfortable with one another’s presence, it’s finally time to remove the barrier. Be sure to supervise their face-to-face meetings, keeping them short initially. It can help to have a family member or friend with you during the first few meetings. Start by having your resident cat already occupied with a pleasurable experience (e.g., a toy, cuddle time, etc.), and then bring in your new cat and immediately engage her. The goal at first is to keep both cats preoccupied with positive experiences so that their entire focus isn’t just on the other cat in the room.

Mild hissing or growling can be normal at first, but if there are signs of aggression or the hissing and growling escalate, redirect the cats with toys. Gradually increase their supervised time together until you’re confident they won’t start fighting.

I spent about a week on this phase because my resident cats were hissing at Monk a lot at first. I found taking it slowly with short times together helped them gradually get used to the new situation.

Once Comfortable, You Can Leave Them Home Alone

While you’re in the process of having your cats physically together, it can be wise to keep them physically separated when there’s no supervision possible. This step may not be necessary if your kitties are showing positive signs. But if not, keeping them separate when you’re away can help over the long term until they get used to each other.

9 Warning Signs When Introducing Cats

Couple of Ragdoll cats.
Following these steps, you should have happy cohabitating cats.

Before you start your cat introductions, it’s helpful to familiarize yourself with the warning signs to look out for throughout the entire process.

  1. Intense staring at each other: A stare-down is a common way cats size each other up, but if it goes on for too long or you notice other warning signs, it’s time to separate them.
  2. Dilated pupils: Wide open eyes and dilated pupils are signs that a cat is nervous and feeling defensive. It usually occurs when they first see each other.
  3. Flattening their ears: When cats’ ears are lying flat or turned backward or sideways, it means they’re feeling threatened or annoyed by the other cat.
  4. Puffed-up fur: Cats typically puff up their fur as a sign of dominance or fear. When two cats meet, this is a sign that one (or both) are trying to look as big as possible. The more submissive cat will usually puff up larger than the other one.
  5. Swishing tail: If your cat’s tail is twitching back and forth when in the presence of another cat, this can be a sign of agitation. Cats also swish their tails when they’re excited, so pay attention to other cues.
  6. Growling: Growling is a normal way cats communicate that they’re feeling uncomfortable in a situation. Some growling is to be expected, but if it’s prolonged, you may need to slow down your process.
  7. Hissing: Hissing is a natural way cats vocalize that they’re feeling fearful and threatened. It’s a warning sign to stay away. Hissing is extremely common when introducing cats, and it’s usually not a major concern.
  8. Stalking, chasing & hiding: The more submissive cat may slink away and hide under furniture, while the dominant kitty may try to assert his power by stalking and chasing. This is a sign to slow down the process.
  9. Urinating outside the litterbox: You most likely will notice this with your resident cat. It means he’s feeling threatened by the new cat and is defending his turf by marking his territory.

Reading Cat-To-Cat Body Language (Video)

Not sure how to read your cats’ body language when they’re interacting? This video from cat behaviorist guru Jackson Galaxy is a must-see to help you understand what’s going on and what to do about it.

Frequently Asked Questions

Here are some common questions kitty owners have about introducing cats. Don’t see yours here? Ask us in our comments.

Can’t you just put cats in a room together and let them work it out?

No. While this introduction process may seem like overkill to you (and your patience level), it’s crucial for a successful relationship. Sure, some laid-back cats may be fine with each other fairly quickly, but that’s not a chance you want to take. You never know how a cat will react. And “letting them work it out” is a potential recipe for disaster.

What if I have multiple resident cats?

Unfortunately, the best course of action is to introduce the newcomer to each of your current cats separately. I placed one of my resident kitties in a closed-off room so the other one had one-on-one time with Monk.

How much hissing is normal when introducing cats?

Hissing is a natural way for cats to communicate, so don’t be alarmed if one or both of your kitties exhibit this behavior. It may begin as soon as they sense each other through the closed door, but some may not hiss until the full in-person meeting.

My resident kitties didn’t hiss until they were physically in the same room with Monk. It’s been about a month since they’ve all cohabitated together. While there’s still some hissing, it’s decreased a lot. Most of it now is when Monk goes into aggressive play mode with my other cats.

What do I do if a fight breaks out?

Never just let cats work it out with a fight. It’s important to separate them immediately, but don’t try to physically get between them. You could end up being injured by flying claws. Stop the fight by distracting them with a loud noise or another means.

What are the signs that cats are starting to get along?

It can take many cats a good 8-10 months to become friends, and some will merely tolerate each other and never reach the friend zone. Signs cats are starting to get along include:

  • Gently head butting
  • Touching noses
  • Hanging out near each other
  • Grooming each other
  • Sleeping together
  • Play fighting and chasing

After a month from when I fully had all three of my kitties fully cohabitating, they now get along fairly well. Monk and Bammy even occasionally sleep together. It’s so amazing to see such progress, and I think taking the initial stages slowly really helped in my case.

Final Thoughts

Following these steps carefully and heeding the warning signs when introducing cats can be a game changer for a successful and peaceful coexistence. This process can most certainly be a test of your patience. And don’t be discouraged if your feline family members are taking a long time to get along. Most cat behavioral experts agree that this slow approach is your best chance for a harmonious kitty home.

White Cat sitting in cat window perch

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