How to introduce a new cat to your cat

Introduce cats slowly. Keep the newcomer in a separate room, let the cats learn each other's scent first, then let them see each other at a distance and meet for short periods. Plan for days at the least and weeks in many homes. A rushed introduction can leave two cats afraid of each other for a long time.

Cats are territorial. They do not make friends on command, and many adult cats prefer to live alone. Some pairs become close, some settle into polite sharing and some never get along. Good introductions raise the odds of the first two outcomes. You cannot guarantee any of them.

Before the new cat comes home

Take the newcomer to the vet first, if you can. Ask your vet which tests and vaccines the new cat needs before it meets your resident cat. Some infections spread between cats through close contact and shared bowls, and your vet can advise about testing for them.

Set up a separate room for the newcomer with its own food, water, litter box, bed, scratching post and hiding place. A door that closes fully is best. Do not use the resident cat's favourite sleeping spot or toys, because the resident should not lose anything it values.

Count your resources. Each cat needs its own litter box and a spare, and food, water and resting places in more than one location. The litter boxes and new-cat checklist tool gives a quick way to count boxes for a multi-cat household.

Keep the resident's routine the same. Feed it at the usual time, give the same attention and keep its spaces open to it.

Step 1: separate rooms and scent

Bring the new cat home in a cat carrier and put it straight into its room. Let it settle. Spend time with each cat separately and give each a normal day.

Cats read the world by smell, so start with scent. After a few days, rub a clean soft cloth on one cat's cheeks and give it to the other cat to sniff. Swap blankets or bedding. Watch the reaction. Sniffing, then walking away calmly is a good sign. Hissing or growling at the cloth means the cat needs more time.

Feed both cats on either side of the closed door, a little way back from it at first. Move the bowls closer by small steps over several meals. This builds a link between the other cat's smell and something good. If either cat stops eating, stays at a distance or shows tension, move the bowls back.

A plug-in pheromone diffuser in each room helps some cats. Evidence for it is mixed, so treat it as an extra and not a fix.

Step 2: swap places

When both cats are eating near the door, swap rooms for short periods. Shut the resident in another room, let the newcomer explore the main house, then let the resident sniff the newcomer's room. Cats learn a lot from each other's scent marking. Keep these sessions calm and short.

Step 3: first sight

Open the door a crack, or use a baby gate or a screen with a gap so the cats can see each other without touching. Offer treats or a meal to both cats as they notice each other. Keep the session to a few minutes and end it while both are still calm.

Read the cats' body language. Good signs are relaxed bodies, soft eyes, slow blinking, sniffing and turning away. Warning signs are staring, flattened ears, a swishing tail, a puffed coat, growling and hissing. A little hissing in the early meetings is common. It tells you to slow down, not to stop.

If one cat lunges, do not grab either one. Make a loud neutral noise, drop a thick towel between them or block their view with a board. Then return to the previous step.

Step 4: short meetings in the same space

When the cats are relaxed at the gate for several sessions, let them share a room while you are there. Start with play and food. A wand toy held between them gives both cats something else to focus on. Provide high places so each cat can leave the situation. Several exits keep either cat from being cornered. A cat that can retreat will often stay and watch.

Keep sessions short at first. Lengthen them over days. Separate the cats whenever you are out and at night until you are sure they are safe alone together. That may take weeks.

Step 5: unsupervised time

Allow the cats to share space alone only when they eat, play and rest in the same area without tension for a long period. Even then, keep separate resources and watch for slow bullying. Some cats guard doorways, litter boxes or food without any noise. One cat that hides more, loses weight or avoids the litter box may be under pressure, even if there are no fights.

Common mistakes

• Letting the cats meet on the first day. Territory and fear make this the riskiest moment.
• Holding both cats and forcing a meeting. A frightened cat in your arms can scratch you badly.
• Punishing hissing. Hissing is a warning. Punishment makes it harder for a cat to give warnings.
• Using one litter box or one bowl. Competition for resources causes trouble.
• Skipping the vet visit. A new cat can carry infections that are not obvious.
• Moving too fast because things look fine. A cat that is silent may be frozen with fear.
• Giving up in week one. Some cats need a month or more.

When to ask for help

Call your vet if either cat stops eating for a day or more, hides for days, shows sudden changes in litter box use, strains to urinate or has red, runny eyes or sneezing. A male cat that strains to urinate or passes little or no urine needs a vet at once. Stress can trigger urinary and other illness, and illness also changes behaviour, so a vet check comes first.

Ask your vet for a referral to a qualified cat behaviour specialist if:

• The cats fight so that one is injured. Any bite wound needs a vet, because cat bites often form abscesses.
• One cat constantly bullies or stalks the other.
• Spraying or soiling starts in the home.
• You have been through the steps more than once and tension remains.

In some cases the safest choice is to keep the cats in separate parts of the home or to rehome one. That is a hard decision, and a behaviour specialist can help you weigh it.

Summary

• Quarantine and vet-check the newcomer first.
• Start with separate rooms and swap scent.
• Feed near the door, then use sight barriers, then short meetings.
• Give every cat its own resources and high places to escape.
• Move on only when both cats are relaxed.
• Call your vet or a behaviour specialist when fear, fighting or health changes appear.