Why cats fight, and how to calm the tension between them

Two cats hissing, chasing and screaming through the house is stressful for everyone, and it's easy to assume the cats simply hate each other or that one is trying to be boss.

Neither is usually the real story. Cats aren't naturally group animals the way dogs are, so living together is something many of them tolerate rather than crave, and most conflict comes down to competition, fear or an introduction that went wrong — each of which has a route back to peace.

Play, or a real fight?

Before you treat a problem, make sure there is one. Cats that are playing chase each other in near-silence, take turns being the one who pounces, pause and reset, and walk away loose and relaxed afterwards.

A real fight is loud — hissing, growling, yowling — with flattened ears, puffed-up fur, swatting with claws out, and sometimes injuries, and one cat that consistently hides, flinches or avoids the other. If the interactions are silent, mutual and role-swapping, that's rough play; reading their body language tells you which you're looking at.

The most reliable single test is what happens next. After play, both cats are loose and neither avoids the other ten minutes later. After a fight, somebody leaves the room and stays gone.

The common causes

Real conflict usually has one of a handful of roots.

A rushed or botched introduction is the classic, leaving two cats permanently braced against each other. Competition for resources — food, water, litter trays, resting spots, warm windowsills, even your attention — manufactures fights where there isn't enough to go around.

Redirected aggression is another: a cat wound up by an outdoor cat it can't reach lashes out at the nearest housemate instead. And fear, or a change in one cat through pain or illness, can turn a settled pair tense seemingly overnight.

Redirected aggression, which looks like nothing else

This one deserves separating out, because it's the cause people most often misread, and treating it as an ordinary feud makes it worse.

The pattern is distinctive. Two cats have been fine for years. One sees a cat outside the window, or hears a fight in the garden, and becomes intensely aroused with nowhere to put it. The nearest housemate walks past at the wrong moment and gets attacked — and from then on, the pair are enemies over an event that had nothing to do with either of them.

What makes it stubborn is that the attacked cat is now frightened of the attacker, the attacker reads that fear as strange, and the relationship keeps confirming itself long after the cat outside has gone.

Two things to do. Block the trigger — window film at cat height, or discouraging the visiting cat from the garden — because the arousal will keep recurring otherwise. And separate the two completely for days rather than hours before starting to rebuild, because a cat that's still aroused can't learn anything and a single repeat sets you back a fortnight.

Resources: the fix people skip

The most overlooked cause is the easiest to fix. Cats fall into conflict when they have to compete for or queue at the things they need, so provide one of each key resource per cat plus one — separate food and water stations, enough litter trays, and plenty of beds and high perches — and spread them around the home rather than clustering them in one room.

Vertical space matters especially: cat trees and shelves let a nervous cat get up and away, and let two cats share a room without being forced into each other's path. Take away the scarcity and you take away a great deal of the fighting. How to arrange a multi-cat home goes through the placement in detail.

Never let them 'fight it out'

It's a stubborn myth that cats will settle their differences if left to it. They won't — letting cats fight entrenches the hostility and risks injuries and infected bite wounds.

Interrupt a fight without getting hurt. Never reach in with your hands, because a cat in that state will redirect a bite onto you. Break the tension with a loud clap, a cushion between them or a towel dropped over one, then separate them into different rooms to calm down completely before any contact resumes.

How long is completely? Longer than it looks. A cat can appear settled within minutes and still be physiologically wound up for hours, which is why the second fight so often follows the first within the same afternoon. Give it the rest of the day.

Cat bites need a vet

Worth saying plainly in its own section, because it's the part that turns a behaviour problem into a medical one.

A cat's tooth makes a deep, narrow puncture that closes over almost immediately, sealing bacteria under the skin. Cat-bite abscesses are extremely common and they develop over a few days — a wound that looked like nothing on Monday is a hot, painful swelling by Thursday.

So a cat that has been bitten in a fight is a cat for the vet, not for watching. The same applies to you: a cat bite on a human hand is one of the injuries A&E takes most seriously, for the same reason.

Re-introduction when it has broken down

When two cats are genuinely feuding, the way back is to treat them like strangers and start the introduction over. Separate them into different parts of the home, swap bedding and scent between them, and feed them on either side of a closed door so good things happen in each other's presence at a safe distance.

Then rebuild slowly to controlled visual contact and finally supervised time together, retreating a step at any sign of real tension. It's the same patient, scent-first process as introducing a new cat, and rushing it is what caused the problem the first time.

Expect it to take weeks rather than days, and expect to go backwards at least once. The single commonest mistake is moving to the next stage because the week is up rather than because the cats are ready.

When it is sudden or severe

Fighting that erupts suddenly between cats that were fine, or one cat that has become unusually aggressive, is worth a vet visit — pain and illness make cats short-tempered, and a hurting cat that lashes out is telling you something a behaviour plan alone will miss.

Cats that lunge or bite hard enough to injure, or a feud that won't ease despite resources and a careful re-introduction, are a good case for a qualified feline behaviourist. And bear in mind that some cats, however well you manage it, are happiest as the only cat — recognising that is kinder than forcing a peace that will never come. The same handling caution applies as with a cat that bites when petted: never punish, and give space rather than pushing.

Managing a feud day to day

While you work on the underlying relationship, day-to-day management keeps the peace and prevents rehearsal, because every fight makes the next one more likely.

Keep the cats apart when you can't supervise, use height and separate rooms so each has somewhere to be that the other is not, and watch for the flashpoints — a narrow doorway, the single food bowl, the one sunny windowsill — and defuse them by adding duplicates and widening the routes between resources.

If one cat corners or stalks the other, give the victim safe zones it can reach and the aggressor can't follow, such as a high shelf or a room behind a gate.

Reducing the number of tense encounters is half the work. The calmer the cats are day to day, the faster a re-introduction takes hold.

What not to do

Four things make it worse, and all four are common.

Punishment of any kind. A sprayed, shouted-at or shut-away cat is a more anxious cat, and anxiety is the fuel underneath most of this.

Holding the cats together to show them it's fine. It isn't fine, from their side, and restraint removes the exit that makes the situation bearable.

Comforting only the victim. It's the natural instinct and it leaves the other cat with an additional reason to resent the first — attention is a resource like any other.

And getting a third cat to dilute the tension. It's occasionally suggested and it almost never works: a new territory-holder in a home that already can't accommodate two is another set of chokepoints, not a distraction.