Introduce cats in stages, starting with a secure separate room and moving from scent exchange to barrier-assisted visual contact and then short, supervised meetings. Let the cats’ behavior—not a calendar—set the pace. If either cat becomes distressed or aggressive, separate them and return to an earlier step.
Before the cats meet, set up a separate room
Give the newcomer a quiet, secure room with its own food and water bowls, bed, and litter box. Keep the cats physically apart at first; they can hear and smell one another without being required to interact. A bathroom can work as a temporary small area. The Humane Society of the United States suggests keeping a new cat in a small area for up to a week as one example, not as a universal deadline.
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Make sure the newcomer can settle without being approached by the resident cats. Keep the arrangement easy to maintain so you can continue separation if the cats need more time.
Exchange scents after the newcomer has settled
Once the new cat is adjusted to the home, swap bedding or other scent-bearing items between the cats. International Cat Care recommends introducing scent before the cats see each other and suggests about a week of scent exchange if possible. That is guidance for a gradual introduction, not a required timetable.
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You can also let each cat explore the other cat’s space at different times, while the other cat is elsewhere. This gives them a chance to investigate unfamiliar smells without meeting face to face.
Let them see each other through a secure barrier
Use a glass or mesh door, a secure baby gate, or another barrier that prevents contact while allowing the cats to see one another. Choose a setup that is stable and gives each cat room to retreat. International Cat Care suggests partially covering the barrier at first, which can reduce the intensity of the view.
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Offer food on each side at a distance where both cats can remain comfortable. The Humane Society recommends gradually adjusting the distance or opening as the cats tolerate visual contact. Keep sessions calm and brief; if either cat appears distressed, increase distance or cover the barrier again rather than pushing ahead.
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When both cats can remain relaxed around the barrier, try a brief meeting in a shared room. Keep the room quiet, supervise closely, and reward calm behavior. If possible, have one person watch each cat so both can be monitored. End the meeting and restore separation if aggression develops.
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For cats being reintroduced after established aggression, ASPCA recommends daily supervised sessions that gradually bring them closer. Keep sessions short, use food or play as a distraction, and separate the cats between sessions. ASPCA advises waiting until they can eat and play peacefully within a couple of feet before allowing unsupervised access; begin with short periods together and increase them gradually.
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Hissing, growling, spitting, and swatting are signs to increase distance and slow down. Separate the cats calmly and return to an earlier step, such as scent exchange or barrier contact. A hiss alone does not prove the relationship has failed, but it does mean the current level of contact is too much for at least one cat.
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There is no fixed introduction deadline. International Cat Care’s suggestion of about a week of scent exchange and ASPCA’s note that severe reintroductions can take several days to a few weeks are examples, not a schedule that applies to every household. Some cats need a longer gradual process.
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Choose a compatible companion, not just a kitten
A kitten is not automatically the easiest choice for a resident cat. The Humane Society cautions that a kitten’s energy and behavior may stress some adult cats. Consider the resident cats’ individual temperaments and look for a good fit rather than assuming a particular age or sex will work best.
Get help if conflict persists
If the cats continue to have serious conflict despite a gradual reintroduction, ask a qualified behavior professional for help. ASPCA identifies Certified Applied Animal Behaviorists (CAAB or ACAAB) and board-certified veterinary behaviorists (Dip ACVB) as options. In some households, long-term separation or rehoming may be more humane than chronic stressful coexistence; not every pair of cats will become friends.
ASPCA also mentions pheromones as something to try during aggression management. Treat them as an optional aid, not a guaranteed fix or a substitute for separation and gradual reintroduction.
Quick Recap
Sources
- International Cat Care, Caring for your new kitten (2024)
- Humane Society of the United States, Top 15 tips for keeping your cat happy and healthy
- ASPCA, Aggression Between Cats in Your Household
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