Do You Know These Warning Signs When Introducing Cats?

There’s nothing as exciting as welcoming a new cat into your home. But if you already have a cat, what are the warning signs when introducing cats that you should look out for? And what are the safest and most effective ways to ensure your cats get along?

A quick overview of introducing cats

Are you thinking about getting a second cat? Do you want to make sure that your resident cat and new cat get along? Know this: cats are sensitive creatures who don’t easily handle abrupt changes.

Because of this, being prepared and taking the time to put a strategy into place is everything. 

Try to put yourself in your companion kitty’s paws for a moment. How would you feel if a stranger suddenly barged into your place? Imagine what emotions would come over you when you saw them raiding your fridge, eating your food, and making a mess out of your bathroom.

As humans, we can communicate when we’ve had enough with our words. We could insist on setting up boundaries and sort out a way to share the space we’re in. We could come to reasonable agreements about how to act in shared spaces and what we expect of each other.

With cats, it’s not so easy.

Along with being sensitive to change, cats are naturally territorial.

Even if you took care to match personalities, bringing a new cat into your home is a stressful event.

Your priority when introducing cats is to be mindful of your cats.

This means being aware of your cat’s body language, keeping an eye out for behavioral problems, and above all, putting the safety of both of your cats first.

So let’s get into the warning signs to look out for when introducing cats.

Common warning signs when introducing cats

First, we have to express again that the introduction period is a process, and it takes time. There are no shortcuts or secret hacks. There’s no instant way to guarantee a perfect introduction.

And sometimes things get hairy. A botched introduction could end in your resident cat and your new cat lashing out at each other (inter-cat aggression) or even you!

But before they get to that point of no return, you can intervene and smooth things over. It’s not all about behavior either. Your cat’s body language and vocalizations are a great way to get a read of how they’re feeling.

warning signs when introducing cats hissing

Here are the most significant physical inter-cat aggression warning signs when introducing cats:

  • Hissing or growling
  • Flattened ears
  • Large, dilated eyes
  • Thrashing or thumping tail
  • Swiping with claws out
  • Hair standing up on end and arched back

What are the most common mistakes when introducing cats?

The most common mistake when introducing cats is one of the most enduring. The old “wisdom” that says it’s best to let cats “work it out” independently.

Jackson Galaxy says that this is a recipe for failure and disaster. This “trigger[s] the territorial panic switch in your existing cat,” and creates a “long-term lack of trust between the cats.”

Another common mistake is plopping your new cat in a carrier and setting them in the middle of a room.

Paws Whiskers and Claws Feline Hospital says this is “incredibly stressful.” This technique allows your resident cat to circle the carrier, “mak[ing] the new cats feel like prey.”

Another negative first encounter is forcing the two cats together.

Physically restraining the cats with leashes, harnesses, or even your hands to make the two face each other is one of the worst things you can do. This is extremely stressful and can be dangerous for the cats and yourself. The cats can lash out at you or the other cat and cause serious injuries.

Cat Introductions Gone Wrong: They Will NOT Work it Out Without You

What happens if you introduce cats too quickly?

Physical aggression and violence isn’t the only thing that can happen if you introduce cats too quickly.

What if you introduce cats too quickly and the interaction goes badly?

It could result in subtler aggression and manifest in behavioral problems like:

  • Peeing or pooping outside of their litter box
  • Hiding for hours or days at a time
  • Cats fleeing from each other
  • Overgrooming and excessive hair loss
  • Redirected aggression where your cat attacks or lashes out at you, other pets, or other innocent bystanders in your household

Certified animal behavior consultant Pam Johnson-Bennett says that for both cats, “abrupt introductions will cause them to go into survival mode.”

Johnson-Bennett agrees with Galaxy that this means “they will start their relationship being hostile toward each other. . . [and] in some cases, that hostility may ease as time goes on, [but] it more often sets the tone for the relationship from that point on.”

warning signs when introducing cats fighting

How can I safely break up a catfight?

You can safely break up a catfight by:

  • Distracting them with noisy toys
  • Place a sheet of cardboard between the cats to quickly break them up
  • Trying pheromone products
  • Draping a blanket or towel over the cats

How long does it take for cats to get used to each other?

Every cat is an individual so it’s better to consider more generalized time frames.

Veterinarians at Paws Whiskers and Claws say that while cats may be able to exist in the same space together within a few days or weeks, it could take “six months or more before they [can] live peacefully under the same roof.”

That doesn’t necessarily mean that your cats will become BFFs either.

The ASPCA says it could take as long as 8 to 12 months for your kitties to strike up a friendship. Or, in some cases, they may, in the words of Mr. Darcy, find their new feline companion merely “tolerable.” Meowch.

How can I choose the right cats to put together?

If you are thinking about getting a second cat, you need to make sure that you find the right cat to pair with your current one.

Remember that your resident kitty has lived a life as the only cat in the house. Getting another cat is going to be an adjustment, no matter how friendly or outgoing they are.

Here’s what you need to take into consideration before introducing cats:


We don’t have a ton of information about age-related compatibility between cats. The facts we do have often come from small studies and sample sizes.

Some feline researchers, veterinarians, and behaviorists say that adult cats pair best with kittens. Others make a case for choosing a cat who’s close in age to your current cat, especially if they’re a senior cat. Some experts even argue that adopting a kitten could put undue stress on your senior cat. And, if they’re already ill, could potentially shorten what remains of their life.

Energy level

It’s best to adopt a new cat with the same or similar energy levels as your current cat.

Questions to ask yourself when considering a cat’s energy levels are:

“How much time does my cat spend playing with toys?”

“Does my cat greet friends and family members when they come home, or do they hide?”

“Does my cat like to run around the house?”

“Do they spend most of their time sleeping in the sun?”

warning signs when introducing cats personality


“Personality can have a profound effect on how two cats may get along,” says veterinarians Debra Horwitz, DVM, and Gary Landsberg, DVM.

Animal behaviorist Megan Maxwell agrees, adding, “the more you can get cat personalities to match, the better. Cats that are similar in personality are more likely to hit it off.”

When it comes to compatibility, personality is the number one factor you take into consideration. So, if your cat is friendly and outgoing or shy and affectionate, then you may want to find another cat that also shares those qualities.


Before bringing a new cat into your home, you need to make sure both they and your current cat have a good bill of health.

Certain medical conditions can make it even more difficult or even dangerous for your resident cat to adjust to sharing its life with a new cat.

Most importantly, you need to make sure that you’re not bringing a FeLV+ cat into a home with FeLV negative cats. Also known as Feline Leukemia Virus, FeLV is highly contagious. Any kind of close contact, including grooming, drinking from shared water bowls, and using the same litter box, can spread FeLV to other cats.

Unless you already have a FeLV+ positive cat, it’s best not to bring an infected kitty into your home.

Fungal infections like ringworm are also highly contagious and transmissible. If your new kitty has this it’s best to hold off on any introductions until they’ve recovered.


As individuals, neutered male cats tend to be more accepting of new cats. When it comes to pairs, some researchers have found that opposite-sex pairs of cats are most likely to get along. In the case of same-sex pairs, research indicates that two males are likely to be most compatible.

The Do's & Don'ts of Introducing Cats

The basics of how to introduce cats

It’s important to know that patience is key. Even if the introduction process appears to be going smoothly, you absolutely must continue to take a steady and gradual approach.

Rushing to put the new cats together is one of the biggest mistakes you can make and it could have lasting negative consequences. Here are the quick basics of how to successfully introduce cats. (You can find a more in-depth breakdown of the introduction process in this article.)

The 1-2-3s of introducing cats

Introducing cats can be broken down into three basic steps, or stages. Before starting this process be sure that your house is ready for your new cat. As much as you may want your new cat and your resident cat to start immediately spending time together resist the temptation to let them loose together. Planning ahead will go a long way in ensuring a less stressful first encounter and keeping your cats safe.

Step 1: Start by keeping the cats separate

Jackson Galaxy emphasizes that each cat have their own “base camp” or personal territory is one of the best ways to manage stress and start your cat’s introduction off on the right paw. This allows your new kitty to get their bearings and to start to get comfortable in its new space, while also providing your resident cat a sense of security and stability.

Step 2: Use common scents and positive reinforcement

Felines are well known for their reliance on their strong sense of smell. Using methods like “scent swapping” is one of the easiest and most reliable ways to start to get your new cat and resident cat acclimated to one another.

In that same vein “site swapping” is also effective. This is when you allow your resident cat to explore the room where you’ve been confining your new cat. And vise versa. By allowing your kitty to sniff out and explore your new cat’s home base, and your new cat to explore your house at large, you help them build confidence and reduce stress and anxiety.

These are a sort of secondhand way to expose them to each other without actually having them square off face-to-face, which could potentially shift into aggression.

Positive reinforcement is also a highly effective tool you have at your disposal. Jackson Galaxy recommends feeding your cats together, but separately, at mealtimes. Meaning, you feed them on either side of the closed door that’s dividing them. Try to place each bowl about 3 feet from the door. This brings both kitties in close contact with each other while bringing the positive association of mealtime with each other’s presence.

Cat Introductions: Good First Impressions are a must!

Step 3: Gradual exposure and supervised time together

Galaxy refers to this step as “eat, play, love”. The gist of this step is to physically bring both of your cats together while continuing to use positive reinforcement. You start off this step by making use of a baby gate or pet gate and allow your new cat and resident cat to look at and sniff each other with the added safety of a see-through barrier dividing them. As your cats become accustomed to each other, you could bring them into the same space.

It’s crucial to supervise both cats during the entirety of their time together in a shared space. It’s especially helpful to continue to use positive reinforcement like feeding them meals and treats and playing with them with their favorite toys.

As you gradually increase their time together you’ll be able to get to the point where you no longer need barriers!

Other tips for a positive cat introduction

Try using pheromone products

The American Association of Feline Practitioners suggests trying pheromone products when introducing cats. Pheromone products come in many forms, including plug-in diffusers, collars, wipes, and sprays.

Veterinarian and animal behaviorist Jacqui Neilson, DVM, DACVB, says that pheromone “therapy” is one of the best tools you could use. Herbal-based imitation feline pheromones help target and reduce stress-related behaviors, aggression, and anxiety.

But these aren’t a single solution. The best way to use pheromones to help introduce cats is with social interaction and behavioral therapies.

warning signs when introducing cats free feeding

Avoid free-feeding

One of the most common reasons why fights break out has to do with food. Simply put, cats don’t like sharing their food. The best way to combat food aggression is to make sure you have enough resources and enough space.

Leaving out bowls of food in one space at all hours, otherwise known as free-feeding, when you’re first introducing cats is one of the biggest mistakes.

This is because food is one of the most valuable resources in your kitty’s life. If they have any kind of food insecurity, they’ll often fight tooth and claw to guard their bowl against the hungry jaws of other cats. Or, they could bully and attack other cats to monopolize all of the food bowls.

Ensure that you provide each cat with its own food bowl and feeding area. Preferably in different parts of the house. You could even try feeding the cats different foods at separate times to reduce the likelihood of your kitties competing over available food.

This is one of the best preventative measures you can take and goes a long way toward limiting fights.

How do you know when your cats are ready to meet?

Generally, cats can meet face to face with a barrier between them, like a pet or baby gate, after a week.

But, as we explored in our multi-step introduction process, your cats will periodically meet in each stage.

The time this takes varies between cats. It’s your job to be attentive to your cat’s needs and behavior. You’re responsible for tailoring your introduction strategy to fit them.

Key Takeaways

Introducing cats takes patience. Rushing the introduction along is risky at best and could be fraught with peril at worst. Cats are very sensitive creatures who are slow to accept change and to forge new felines friendships. Knowing the warning signs when introducing cats is one of the best tools you have at your disposal as a cat parent.

Above all, know that your cat is an individual. Have confidence that even if you make mistakes along the way that you have the tools to make any cat introduction a success.

Victoria Tomis