Cat Relationships 101:

Cats are often portrayed as “solitary” creatures. However, cats in the wild will quite readily and frequently choose to live in colonies, usually consisting of one intact dominant male and/or several subservient intact or neutered males, and a harem of females (both intact and spayed). When it comes to feline behavior and interacting with others, the two most important things are Scent and Territory.

Cats recognize others from their colony by scent, which is why you often see cats from the same family or colony rubbing against each other, usually starting at the head then running along the body and then raising their rear to put the base of their tail and rump against the other cat. They are sharing pheromones from scent glands on their body, creating a combined scent that is unique to that specific group. Cats also mark their territory by spraying urine (generally only intact animals do this), rubbing their cheeks along trees, bushes, and manmade objects to leave scent marks, and scratching on objects — which leaves not only a scent marker from the pads on their feet, but also a visual marker. This territorial marking is shared by all the cats within a colony, and contributes to the combined group scent signature.

When two cats meet, they almost always sniff one another on the muzzle/mouth/cheeks and also the base of the tail or rear end. They are utilizing the scent glands located in these two areas to determine whether this cat is a known, established cat in their colony’s hierarchy or a foreigner, and thus determining the response they give. Cats also have a very good memory, and can remember whether another cat they’ve recently seen is a known or unknown individual, which can dictate how future interactions play out.

If an unknown cat wanders into the established territory of a colony, they will often unite and attack or run the intruder off. This not only protects their offspring from intruding males, but also protects resources and familiar hunting/shelter spots. Territory is very fiercely protected.

Indoor pet cats behave in the much the same way, and rely on the same scent and familiarity to determine whether to accept another cat’s presence or not. The majority of cats will first sniff an unknown individual, then react by hissing/growling and either running or attacking. Their instinct is to protect themselves and their perceived territory within their household. The same will often happen if one cat from a household is taken to a groomer or to the vet, and comes home smelling unfamiliar. The cat(s) at home will often hiss or be less tolerant until the cat who left returns to smelling like the shared colony scent after a few days. Like their wild and feral counterparts, indoor cats also have a very good memory, and initial interactions with new household additions can either make or break their future relationship and colony (family) harmony.

Kittens usually adapt to new homes and housemates pretty quickly, and the adults in the home often accept kittens fairly quickly. Adult cats often need more time and a slower process. The established current cat(s) need to feel that their territory is not being invaded or taken away, and the new cat(s) need to feel that they can establish their own territory at their own pace without feeling threatened. These 2 issues are where most owners make mistakes and end up with problems.

Over my lifelong existence surrounded by cats – with personal pets, 30+ years of rescuing, and my veterinary career – I’ve spent countless hours observing feline behavior and discovering the best ways to approach important issues. I’m also far from alone in this endeavor as famous behaviorists like Jackson Galaxy have done the same, and we often arrive at the same conclusions — this being one of them, and it works EVERY time if you take the time to do it correctly.

Trust the process, do not rush the process!

So without further ado, here are the 4 steps to successfully introducing a new cat/kitten into your home with your existing furkids!

Step 1: Non-Visual Introduction

When you bring your new kitten/cat home, place them in their own bedroom to start with, separate from your established cat. The room they are placed in must be quiet and calm, and have a door that can be kept shut. To help them settle in, utilize Feliway Comfort Zone diffuser plug-ins as well as their spray version. This mimics the comforting familiar pheromones that cats produce in their cheeks when marking their “home” territory, and helps cats feel at ease. They make a HUGE difference. Let your new kitty settle alone in their room for at least a week, possibly two for more shy or stressed cats.

You should go in and spend at least an hour or more with them every day, in addition to the time you spend feeding them and scooping their litter, so that they can bond with you and receive attention. I often recommend sitting or lying in the room and watching TV, reading a book, listening to music, or scrolling on your phone, so that the cat can get used to you in a non-confronting way and choose whether they want to interact with you or just sniff and explore you first. They also can then snuggle with you. It also helps to play using wand toys or Da Bird to give them exercise and appropriate mental and physical stimulation. Ensure they have multiple other self-play toys and a scratching post or cat tree in this room as well.

During this settling period, you should take any blankets or clothing that your established cats have laid on and “pet” the new cat with them or rub them down with these fabrics. This helps begin the scent exchange and creating a new colony scent. I know, it sounds silly. But trust me, this makes a really big difference in how quickly and easily they accept each other!

After the new kitty has had time to settle in and seems comfortable, you can start giving the cats “swap time” — this is when you let the new cat out in the rest of the house to explore for a few hours while your existing cat(s) stays in the new cat’s bedroom. This allows them to explore each others’ smells and territory in a non-threatening way, and aids in scent exchange. Do this for at least a week, preferably two, usually 2-3 hours each time. This step is super important so do not rush or try to shorten it.

Step 2: Controlled Exposure

This step allows the cats to meet one another in a safe, non-threatening manner. I usually recommend allowing them to sniff noses under the door at first. You can encourage this by placing treats under the door or a toy to draw them both to it. Do this for a few days, multiple times per day for short periods, maybe 5-10 minutes at a time at most, maybe 15 if it is going very well. If your flooring does not allow any gap under the door, then you can skip this initial part.

After this, you can move on to more direct exposure, which involves putting a baby gate (a $10 generic wood one is perfect) in the bedroom doorway. Then you sit with the new cat on one side, preferably with your partner or a friend sitting with your established cat(s) on the other side. Then before either cat can react, you provide both with a REALLY yummy, high value treat. Plain low-sodium turkey lunch meat or cooked chicken breast works really well for this! You continue to keep giving each cat a treat in order to keep them distracted and in a positive mindset. One treat at a time, you don’t want them to fill up.

A small amount of mild hissing, even a small amount of grumbling is normal. Cats should be allowed to vocalize how they feel, provided it is not severe.

If the cats are extremely reactive to one another, put a towel over the baby gate to block their view of each other. This still allows them to smell and hear each other while receiving the positive reinforcement (treats). You can also use commercial cat treats like Temptations. No human food other than bland cooked meat. The key with this step is to only give VERY tiny pieces of treats, so that they stay busy and don’t fill up quickly and decide they want to walk away.

Feeding tasty treats to both cats at the same time teaches them to associate each other’s sight/scent with very positive feelings. You should also continue doing scent rub downs and territory swaps in order to continue assimilating them into the same colony identity. Do this for a week or two depending on the cats’ progress. 

Step 3: Face to Face

Once the second step is going well and they tolerate each other on opposite sides of the gate, you can now open the bedroom door for a few hours each day and allow them to freely choose how much they want to interact. Don’t bring them to each other or force it, just supervise and let them decide.

If the newcomer is a kitten, you should play with them for at least 30 minutes prior to opening the door, so that they will have burned off that extra energy and won’t immediately bombard the established adult cat(s) with play advances. This should also be done if the new addition is younger than 5 years old and/or has a boisterous personality that risks being too overwhelming right off the bat and pushing the established cat(s) into feeling threatened. A worn out kitten is a happy kitten!

As mentioned in Step 2, a little passive hissing in their first meetings is perfectly fine — they have to be able to communicate with each other to express boundaries and personal space, and tell each other how much interaction is OK.

It really helps to provide a positive interactive toy like a laser pointer or wand toys or Da Bird, something to steer their focus toward that toy rather than each other while they are out together. Wand toys with feathers and long fleece ribbons work really well with kittens. Do this for a few hours each morning or afternoon, and keep the newcomer in his/her bedroom for the rest of of the day so that neither are pushed past their limit. You can still do space swaps to aid in settling. This stage should last 5-10 days depending on how well they are doing.

Step 4: FINALLY!

If all is going well and both cats seem to have accepted each other for the most part, then you’ve finally reached the point where the newcomer can start staying out with everyone 24-7. You can encourage them in your home by using pheromone diffusers regularly and by placing multiple cat trees and scratching posts around the home, so that each cat can feel they have their own territory that they can claim ownership of but also seek comfort and protection in. They will often share beds and cat trees as part of their shared colony resources, but cats still generally have unspoken ownership or “favorites”.

However, there’s a caveat: If at ANY point there are any fights (other than a very passive hiss, grumble, or single smack here or there, that’s just communication), or either cat seems stressed, scared, or picked on, then they MUST be separated back to their areas and start over the next day with the previous stage. Do this for as long as needed, and continue to utilize scent swapping, , pheromone sprays, and everything in your newfound toolbox to create a multi-cat home in harmony!

A final few words…

Usually with kittens, this entire process only takes 1-2 weeks or so before they’re mostly adapted. But it can take a month or more with older cats or for established cats to accept the newcomer. The big thing is NEVER rushing it or pushing them — if they have negative interactions, they will remember those and it will establish the type of interactions they have in the future. Everything should always be positive or neutral, and it always helps to reinforce with positive things like treats, toys, petting, etc.

Joining a new household or having new cats join an existing household may cause stress for the cats involved and cause illness to flare up. Usually this involves a flare up of Feline Herpes Virus (FHV), which over 80% of domestic cats have. It is generally harmless, and lies dormant in most cats, with rare occasional flares here and there that result in runny eyes, mild sneezing, etc. This should resolve on its own and should not involve any green or yellow mucous – if they develop more severe respiratory symptoms with yellow/green mucus discharge; this is likely a bacterial infection and requires veterinary care. But very mild watery eyes and sneezing is usually no concern.

It should also go without saying, but before adding ANY cat to your family, both the new kitty and your established cats should be tested for FIV/FeLV, fully vaccinated, spayed/neutered, and their nails trimmed or covered with SoftClaws to prevent injury. NEVER declaw your kitten or cat, as it is an incredibly cruel and outdated procedure with lifelong behavioral and physiological ramifications.

Congrats and Best Wishes!