Skip to main content

Why do cats open their mouths when they smell? It’s for a really cool reason

The Flehmen response is a little-known reaction in felines that allows them to take in more of their surroundings

A black cat's close up with an open mouth
Dids / Pixabay

Think of the last time you smelled something foul. How did you react? If you’re truly made of steel, you may not have reacted at all, but for most people, it’s impossible not to flare your nostrils at least. You may have even made a face! All of these reactions are perfectly natural, though humans aren’t the only species that reacts to smells, both good and bad. Even your cuddly cat sniffs out the world around them sometimes,

If you’ve ever noticed your cat reacting to a smell, you’re not alone. Some folks have even noticed their cat opening their mouth — and even sticking out their tongue — while smelling, but it’s not so clear what this means. Is this a reaction to a scent, or is it just a way to get an extra thorough sniff? Whatever it may be, we’re here to find out.

Needless to say, you’re not alone if you’re wondering, “Why do cats open their mouths when they smell?” We’ve scoured trusted sources to find out, and this is what we know.

A white and tabby cat with their mouth open
ariannassz / Unsplash

Why do cats open their mouths when they smell?

Watching your curious cat open their mouth in a kind of sneer while they get a good sniff of something can raise a lot of questions — it’s understandable. When people do this, it’s usually a response to an unpleasant smell, but when cats do this, they’re actually trying to get a better understanding of the scent in the air.

This is called the Flehmen response. Many cats involuntarily have this response when exposed to certain intriguing scents, though cats aren’t the only species that do this. Big cat species like lions and tigers do this, too, according to the animal experts at PetMD, as do horses, sheep, goats, and even dogs. Rhinos, llamas, giraffes, and other exotic animals have been seen performing this behavior, too.

An old orange cat meowing
Thomas K / Pixabay

What is the Flehmen response?

Although it seems like a cat opens their mouth as part of a facial expression, it actually has a physical purpose. Cats have an organ between the nasal cavity and the roof of the mouth called the vomeronasal organ, or Jacobson’s organ, which processes the hormones and pheromones contained within a scent. Veterinarian Krista Seraydar describes this process as “a combination of taste and smell.” Cats access this response by letting air — and its scent — pass through the mouth and into the opening of the Jacobson’s organ. So that’s why your cat is sitting next to that stinky sock with their mouth hanging open.

You might see your feline friend curling their upper lip, extending their neck, and holding their head high in the air. They may even bare their front teeth. In most cases, a cat may stay in this mouth-open position for a few seconds while they process the smell, but don’t be surprised if your kitty takes a little bit longer sometimes. They may appear to be panting, sneering, or even sneezing, but rest assured, this is all perfectly normal.

Cat looks up at camera with mouth open
fantom_rd / Shutterstock

Why do cats react with the Flehmen response?

Although it may seem like cats choose random times to process their surroundings’ scents and pheromones, the simple truth is that some scents just don’t trigger this response. According to Dr. Seraydar, the most common triggers of the Flehmen response in domestic cats include:

  • Urine
  • Dirty laundry
  • Anal gland secretions
  • Pheromones from other cats
  • New scents
  • Anything intriguing

While this is typically used among male cats to detect females in heat, cats of any gender can use this response to explore any scent. Maybe they’re trying to get a good whiff of your friend’s cat whose scent is on your pants, or maybe they won’t leave your suitcase alone after traveling somewhere new. Your kitty could be exploring just about any scent.

And just to be clear, their facial expressions don’t mean that your cat finds these scents stinky or gross. That’s just the way their face moves to let the air into the Jacobson’s gland. So there’s no need to be offended if your kitty seems to sneer at you after giving you a sniff, we promise.

Calico cat with mouth open
GK Hart / Vikki Hart / Getty Images

When your cat’s open mouth may be a problem

Although the Flehmen response is totally normal among felines, there are times when a cat’s open mouth could actually be an indicator of a problem. When smelling, a cat’s mouth will stay open for a few seconds, but if their mouth stays open for a long time, keep an eye on your pet. If you notice anything like erratic breathing or panting, something may be going on.

As Greencross Vets reminds readers, cats only pant when they are very hot, very stressed, or fighting an illness. Some amount of open-mouth breathing is normal when a feline is exercising or has just been outside in warm weather, for example, but continuous feline panting is worth a closer look. Greencross Vets recommends checking your kitty’s gums for a healthy pink color. If you see pale, white, gray, or even blue gums, take your furry friend to the vet immediately.

For the most part, a cat smelling with their mouth open is completely normal. In fact, it’s rather helpful, too. Felines can learn a lot from the pheromones and hormones hidden within a scent, so don’t be concerned if you see your cat making a “stinky” face every now and again.

Editors' Recommendations

Gabrielle LaFrank
Gabrielle LaFrank has written for sites such as Psych2Go, Elite Daily, and, currently, PawTracks. When she's not writing, you…
Why do cats have 9 lives? The origins of the saying
Here's what we found out about cats and their many lives
A tabby cat looks up eith blue eyes

Whether you've lived with cats in your home all your life or have never even gotten close enough to pet one, there are a few feline facts, myths, and stereotypes that you're bound to have heard. Cat characters in TV shows and movies are great at perpetuating this knowledge, though no one can confirm or deny these feline fun facts and generalizations quite like the pets we know and love.

It doesn't take long to learn that cats can have a huge attitude, for example, or that they don't always get along well with other animals like dogs do. It's easy to understand why cat owners and feline fans alike can get caught up in these stereotypes. But at the same time, other feline fun facts -- like why cats are said to have 9 lives -- remain shrouded in mystery.
Until now! We've done some digging into the origin and accuracy of the old saying: "Why do cats have 9 lives," and here's what we uncovered.

Read more
Why you should feel honored if your cat sleeps at your feet
If you've ever wondered about this cat behavior, this article is for you
Calico cat lying on a white comforter

Have you noticed that when you go to sleep, your cat automatically heads to the foot of the bed and curls up by your feet? It's no mistake, and it's not your cat giving you the cold shoulder, either. This is a deliberate decision on your kitty's part, and there are many reasons why they might choose to sleep there instead of curling up on your stomach or by your shoulder. In fact, if your cat sleeps by your feet, you should take it as a compliment and feel flattered.

So, why do cats sleep at your feet? It's a mix of your cat's affection for you, a feeling of safety, and even the body heat you generate that play into your cat's decision to sleep at the foot of the bed.

Read more
4 reasons why cats wag their tails while lying down
This behavior is almost always never something to worry about
Cat yawns while sitting in a window

We know all about dog tail wagging, and most pet owners can spot the difference between a happy twitch and a cautious one. But did you realize that cats use their tails to express themselves, too? Like with dogs, the cat tail swish could mean a few different things, and it's important to have some sense of feline behavior — and your specific kitty — to decipher their movements. So why do cats wag their tails while lying down? We'll walk you through the most common causes and when you might need to step in.

Why do cats wag their tails while lying down?
If you stumble upon your kitty lying down and only moving their tail, it's probably because of one of these four reasons.
They feel happy or playful
You might see your cat lying lazily in the sun, but suddenly they give a little tail twitch as you approach. It's not your imagination. They're excited to see you and ready to play. Assuming you don't note any signs of aggression (we'll get to those later), you should head on over to pet your cat or grab their favorite toy and start a game.
It's hunting time
We can all picture the lion stalking their prey while slowly moving their tail back and forth — your cat does this, too. Oftentimes, this one will happen when they're lying on a perch or near a window and can spy on birds or small mammals in the yard. It could even be that they've spotted a fly and will pounce at any minute. All you need to do here is reach for your camera and enjoy your silly kitty at their best.
They're stressed
A cat that feels stressed will often floof their tail and start to wag it. Kitties generally puff up their fur to appear larger and more menacing. This action may also combine with an arched back or a hiss. Alternatively, sometimes tail thumping comes from overstimulation. You'll recognize pretty quickly which movements indicate fear and which mean fun.
They're dreaming
Sometimes, you'll observe your mouser twitch their tail while sleeping. It could come from a simple muscle spasm just like you get when you sleep (it also might mean they're hunting down prey in their dreams). Additionally, your sleepy kitty may be, well, faking it. They might look asleep but are actually just resting and waiting for you to come over.

Read more