Understanding Feline Non-Recognition Aggression

by Rita Reimers, Multi Cat Behavior Expert

Have you ever taken one of your cats to the vet, only to come home and find that your other cat reacts like they’ve never seen them before? Hissing, growling, maybe even a full-blown swat fest? If this sounds familiar, welcome to the baffling world of Feline Non-Recognition Aggression (NRA).

No, your cat hasn’t suddenly developed amnesia, but something about their furr-miliar friend now seems… off…

What Is Feline Non-Recognition Aggression

Feline Non-Recognition Aggression occurs when a cat no longer recognizes their feline housemate, usually after one cat has been away—most often for a vet visit or grooming appointment.

This strange behavior is likely due to the returning cat smelling different, whether from medications, other animals at the vet, or even just that weird clinical “vet’s office” scent.

Cats rely heavily on scent for identification, so when their buddy smells unfamiliar, it can trigger a defensive response. Sometimes the aggression may even transfer to their people, too!

Why Does This Happen?

Cats recognize each other primarily by scent rather than sight. When one cat returns home smelling different, the stay-at-home cat may react as if they’re encountering a total stranger—or worse, an intruder. It’s not personal; it’s instinct.

Imagine your best friend leaving for a weekend spa retreat and returning looking the same but smelling like a mix of unfamiliar perfumes, lotions, and maybe a hint of seaweed wrap. You know it’s them, but something doesn’t feel right. Now, imagine that, but instead of mild confusion, your response is to hiss and bat at them. Welcome to the cat version of that scenario.

Signs of Feline Non-Recognition Aggression

• Hissing and growling at the returning cat
• Swatting or chasing
• Blocking access to food, litter boxes, or favorite spots
• Tail puffing and arched backs
• Prolonged avoidance of the returning cat

How to Reintroduce Your Cats and Restore Peace

If your cats suddenly act like mortal enemies, don’t panic! Here’s how to help them remember their long-lost friendship:

1. Give the Returning Cat a “Decontamination Period”

Before reintroducing your cats, keep the returning cat in a separate room for a few hours. This allows them to groom and start smelling more like home again.

2. Swap Scents

Rub both cats with the same towel or blanket to transfer their scents. You can also pet one cat and then the other to help them smell like family again.

3. Use Calming Aids

Calming Aids like Rescue Remedy for Cats or Cat Calm can help reduce tension and promote a calming environment.

Another calming aid we love these Pet Honesty Calming Treats. Of all the calming treats we tried, these were the only ones our cats would eat more than once!

4. Supervised Reintroduction

When reintroducing, keep interactions short and positive. Offer treats or playtime to create positive associations. If tensions flare, separate them and try again later.

5. Time and Patience

Most cases of NRA resolve within a few hours to a couple of days. However, if aggression continues beyond that, consider a full reintroduction process similar to introducing a new cat into the home.

Linda and Rita at Cat Behavior Alliance can create a re-integration plan just for you.

Preventing Non-Recognition Aggression in the Future

• Vet Visits Together: If possible, take both cats to the vet at the same time so they share the same smells and experience.
• Preemptive Scent Swapping: Before bringing a cat home from the vet, rub them with a blanket that smells like home.
• Clean Off Vet Smells: Wipe the returning cat down with an unscented baby wipe or a towel with their own scent.

Final Thoughts

Feline Non-Recognition Aggression may seem dramatic (because, well, cats), but it’s usually temporary.

With a little patience, scent swapping, and maybe a few peace talks (or bribes with treats), your cats should be back to their normal, lovable selves in no time. And remember, to your cat, scent is everything—so don’t take their temporary hostility personally!

Have your cats ever experienced Non-Recognition Aggression?

Share your stories in the comments—we’d love to hear how you restored the peace in your feline kingdom!