My Cat Just Got Home, Now They're Fighting - Help!

Understanding Non-Recognition Aggression in Cats After Leaving Home

For some cats, watching a sibling head off to the vet, groomer or boarding facility is no big deal. But for others, it can trigger serious stress—even full-blown fights. When one cat returns home, they often smell strongly of the vet clinic: the hands of doctors and techs who’ve handled many animals, cleaning agents and disinfectants, and even stress pheromones from their own experience. To the cats at home, this returning feline smells unfamiliar—and possibly threatening which can trigger hissing, swatting, yowling, chasing and other aggressive responses. This is referred to as "non recognition aggression".

In mild cases, this might cause a few hisses or avoidance. In more severe situations, cats who were once bonded can become aggressive or even unable to live peacefully together. So, what can you do if this happens in your home—and how can you prevent it?

Steps to Take Before Your Cat Leaves

Before your cat even leaves prepare a “scent cloth”—a towel or small blanket that carries their natural scent. Rub it on them or leave it in a favorite sleeping spot to gather scent organically.

Prepare a room set up for ONLY your returning cat that includes food, water and litter box where they can camp out for a few hours.

When Your Cat Returns From the Vet, Boarding Facility or Groomer

Once home, don’t immediately reunite them with your other cat(s). Instead:

1. Seclude them in a quiet room. Give them a chance to settle and absolutely NO interactions with the other cats in the home.
   

2. Wipe them down with the pre-scented towel or blanket. This helps reintroduce their familiar scent. Then toss this in the wash!
   

3. Encourage grooming. If your cat enjoys brushing, this may be a good time to do that too as it can help to reduce the unfamiliar smells and return their normal smells.
   

4. If your cat tends to groom after eating, offer a small meal or treat to get them started. Grooming helps spread their scent back over their body and lowers stress.
   

5. Let them decompress. Make sure they have time to use the litter box, eat, drink, and even nap before reintroducing them to their feline housemates.

Reintroducing the Cats

Once the returning cat has calmed down and groomed, begin slow reintroductions with the other cat(s). Here’s how:

• Stay present and calm, monitor all cats behaviors and interactions.
  

• Set up the returning cat something to engage with (food puzzle, bird video or automatic toy) which can remove pressure off initial interactions while the other cat sniffs. Setting them each up with something mutual to do at a distance can be valuable - but be aware your reactive cat is likely to be most interested in the scents your cat has brought home and may not be interested.
  

• Allow the cats to sniff and greet each other, but intervene if either shows signs of arousal or aggression—such as tail lashing, growling, intense staring, or stalking. Also step in if one cat appears to be trying to create distance. Support that need for space. If you need to separate them, avoid picking them up when they're highly aroused, as they may redirect aggression toward you. Instead, use a blanket, cardboard, or a barrier to block their view of each other and safely guide one away. Once separated, ensure they can’t see or access one another. Try reintroducing later, and repeat the process until their interactions remain calm and neutral. DO NOT:

• "Correct", punish or reprimand the cat who may be becoming aggressive (hissing, swatting or chasing the other cat) - these behaviors are a result of fear and insecurity - believing this is a totally different cat. How they feel is valid, do not make it worse by causing more stress.

• Bring cats together by picking them up and showing them to one another. Although our hearts are in the right place to want to fix things quickly, this must go at their pace and forcing interactions may lead to strong, unwanted responses that set you back further. For some cats, especially those with a strong reaction, you may need to do a full reintroduction using a baby gate or gradual scent swapping. This process can take days, weeks, or even longer depending on the severity. Some families have shared that taking cats to the vet together has limited these negative responses, whereas others share it did not make a difference in future occurrences.
  

When to Get Professional Help

It’s strongly recommended to talk with your vet if you're seeing any signs of aggression or stress around reintroductions - especially if your cats are leaving home often. Additionally, reach out to a certified behavior specialist if you are unable to bring the cats together OR are struggling with this process alone.

A Final Note

Non-recognition aggression is common.  Cats navigate their world heavily through scent so when that familiar scent changes, it can create confusion and fear—even among bonded pairs. The first time this happened between my adopted pair of kittens, it really caught me off guard. They’d always been close, so seeing sudden tension between them was hard to watch.

I couldn’t help but wonder: Will things ever go back to normal?  Over time, I figured out what helped and what didn’t. Worrying didn’t do much—but staying calm, having a plan, and talking with our vet made a big difference.

Even now, years later, it still comes up—usually once a year after one of them returns from the vet. But we’ve developed a routine that helps minimize the impact and keeps things manageable for everyone.

If your cats go through something similar, planning ahead makes a big difference. The good news is, with the right strategy, this behavior can be managed. We’ve seen it work.