Why Do Cats Hold Their Mouths Open After Smelling Something?

My childhood Ragdoll cat, Rags, used to leave his mouth open after he smelled things. This happened quite frequently. I began to hate it because it was often after smelling urine or another cat’s butt. But it was pretty rad when I found out what he was doing…so, why do cats hold their mouths open after smelling something?

Ragdoll cat Caymus holding his mouth open to show the cat flehmen response which explains Why Do Cats Hold Their Mouths Open After Smelling Something?
Caymus after smelling Trigg’s butt. Gross. 

You know what I am talking about. It is where the cat leaves its mouth slightly open, dazes off for a second, licks its nose, and closes its mouth again. Last week, I ran across the street to a neighbor’s house to grab their recycle bin that had been at the curb for a few days – I figured they were out of town, so I put the bin behind their house and came back home. When I came back home, Charlie would not stop smelling me; he had that cat, stinky face.

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Cat Caymus showing the Flehmen Reaction in Cats Why Do Cats Hold Their Mouths Open After Smelling Something?
Caymus is still taking it in. April 17, 2010

I couldn’t figure out why until later when I had stopped by my parent’s house, and Caymus wouldn’t leave me alone either – Caymus never shows attention like that, so I knew I had something on me. I came to find out that the recycle bin had been sprayed by a male cat, and I smelled urine on my pants – LOVELY. So when I came home, I immediately changed out of my pants and had Charlie and Trigg give them a good whiff so that I could get a photo for this post!

Trigg Using His Jacobson's Organ
Trigg Using His Jacobson’s Organ

There’s a fantastic website called Pet Tails that lays this out more in detail, and that’s where I got this information.

Flehmen Response Cat:

Cats hold their mouth open after smelling something because of their Jacobson’s organ, a unique sensory organ called the vomeronasal organ or Jacobson’s organ that allows a cat to have 14 times the sense of smell of a human.  The act of opening the mouth and drawing up the air to the Jacobson’s organ is called the “flehmen reaction.”

So, why do cats open their mouth when they smell?

Charlie using his Jacobson's organ sniffing a blanket
Charlie using his Jacobson’s organ

Essentially, the cat is opening her mouth to suck in the air into Jacobson’s organ and sniff the odor intensely.

Charlie's flehmen reaction while he's sitting
Charlie’s flehmen reaction

The Jacobson’s organ, which consists of two fluid-filled sacs that connect to the cat’s nasal cavity, is located on the roof of the mouth behind their teeth.

Charlie licking his nose after the flehmen reaction
Charlie licking his nose after the flehmen reaction

They look dazed for a second or two because they can learn a lot of information about their surroundings through their sense of smell. They mark territory using the scent glands on their cheeks and paws. The glands secrete pheromones, chemical substances that stimulate a behavioral response, such as avoidance or aggressive reaction. Pheromones are also found in saliva, feces, and urine. When cats “spray,” it’s another way they mark territory.

More About the Flehmen Response

It is well-known that cats have a much keener sense of smell than humans, but how they manage to out-sniff us is rare knowledge. Nor is the fact that they have more developed sensory organs than we do. One of these sensory organs is Jacobson’s organ or the vomeronasal organ, which provides them with very detailed information about a particular smell.

Theo the Seal Mitted Ragdoll Smelling while sitting on porch with flowers
Theo is loved by Krista, showing the flehmen’s response.

To use this organ, they must keep their mouths open and breathe through their mouths because its openings are located on the roof of their mouths, just behind their incisors. As they breathe in the smell, the roof of their mouths must be wet with saliva. It is also imperative they only breathe in through their mouths. This is one of the reasons why they make that odd face.

Why Do Cats Hold Their Mouths Open After Smelling Something Selene the Bengal staring at the camera
Selene, the Bengal, loved by Sharon

They pull up their upper lip to permit as much of the smell to enter their mouths. Scientists have described the sensory information moving through the vomeronasal organ as being between smell and taste. This should give you an idea of the complexity of the information provided by this organ. This suggests that cats use their Jacobson’s organ when they want to go into particular detail about a specific smell.

What is the purpose of the flehmen response?

The flehmen response is heavily tied to identifying pheromones, which is extremely important for cats. As such, it plays a considerable role in interspecies communication. The vomeronasal organ is an olfactory-chemosensory organ that can help animals gather chemical messages from their peers. This is precisely why Caymus and Charlie were so interested in sniffing out the urine on the pants. They were taking in the pheromones in the male cat’s urine.

flehmen response in cat

The flehmen response is much stronger in males. This is because they have to be particularly perceptive of the pheromones of females in heat and those of other males. This plays a significant role in the mating process.

This explains why in most cases, cats are using their flehmen’s response to track down smells coming from other cats and check out if another cat’s butt smells. In households with more than one cat, they can be seen displaying the grimace more often.

Moreover, remember that you bring new smells into the house from outside every day. Your cat doesn’t need to go out to sniff the smells of other cats because you are bringing them in for them. Aside from this, cats will use their vomeronasal organs to analyze very intense smells. For instance, you may find them with their mouths open, analyzing your dirty laundry, which is heavily soaked in your scent.

Where is the vomeronasal organ located?

In cats, the vomeronasal organ is located inside the roof of their mouths. It has ducts leading to the mouth and the nose called the nasopalatine canals. You can see two openings on the roof of the cat’s mouth, just behind its incisors. These are the openings to the nasopalatine canals. They are filled with fluid. This makes it impossible for the smell to go up passively from the mouth to the nose.

cat smelling something and opening its mouth

For their sense of smell to travel through the canals, it has to be soaked in saliva and pushed up until they come into contact with the organ’s sensory cells. This is where the intense mouth-breathing comes into place. In addition, by pulling up the upper lip, the openings of the nasopalatine ducts are also more exposed, and the motion propels the saliva-soaked smell up the ducts.

What is flehmen’s grimace?

This is the name for the silly face cats make when using their vomeronasal organ. The term flehmen’s grimace refers to when they pull back their upper lip, expose their teeth, and breathe into their mouths with their eyes fixed at one point. “Grimace” is used precisely to suggest the exaggerated features they display at that moment.

What are other reasons why cats would keep their mouths open?

The flehmen response is a very complex process during which cats get extensive olfactory information, more than we humans will ever know, but it happens quickly. Cats only take seconds to complete the process, after which they snap out of it. The flehmen grimace disappears, and they close their mouths.

If you notice that your cat keeps its mouth open for longer than a minute or two, the reason is not a flehmen’s response. In fact, if your cat keeps its mouth open for a long time, you should look closer to see what happened because it’s not normal. Here are a few things to consider:

Has the cat been running or playing? Sometimes, after intense physical activity, cats might keep their mouths open to take in larger quantities of oxygen. That shouldn’t take more than a few minutes, but definitely longer than the flehmen response. You will also notice your cat breathing heavily, which should stop in a few minutes. If it takes longer than that, or if your cat hasn’t been running or playing, you should call the vet because it might have difficulty breathing, which is a medical emergency. That is the worst-case scenario.

Cats might keep their mouths open because it is uncomfortable for them to close them or because they can’t close them at all. This happens when cats have oral lesions or other issues of the oral cavity.

For example, Gingivitis might cause them significant discomfort, and keeping their mouths open may be a more comfortable position. This usually happens when cats have large amounts of tartar, which leads to the infection of the gums. If the infection extends further than the gums, then it is stomatitis.

Over time, tartar buildup causes periodontal disease. In time, this affects the ligament of the teeth, causing the teeth to fall out. This or other issues with their teeth, such as fractured teeth, can also cause cats pain. Therefore, they keep their mouths open by applying pressure to the affected area to avoid worsening pain.

Other issues that might make them keep their mouths open are tongue lesions or lesions on the roof of the mouth and/or the inside of the cheeks – ranging from cuts and scratches to malignant or benign tumors. Another reason why cats would keep their mouths open is a broken mandible. In this case, they could not close their mouths at all.

If you notice that your cat has been keeping its mouth open for an extended period, try to open it and check for Gingivitis, scratches, cuts, or other issues. Then take your cat to the vet. The doctor will thoroughly examine the oral cavity to determine why your cat keeps its mouth open.

How do cats react when they smell something bad?

First, we should clarify that what we humans regard as “something bad” might smell very inviting to your cat. Raw fish, for instance, might make us turn away, but it will surely spark the interest of cats. Unfortunately, the opposite is true – sometimes, what smells great to us might smell very bad for cats.

So, when cats smell something they regard as bad, they tend to shrug and wrinkle their noses and then do their best to escape the smell as quickly as possible. But if you want to see it in action, give your cat a slice of lemon to smell. It will vacate the premises in no time.

In this regard, the bad smells, not necessarily the lemon, to cats are similar to us humans – they shrug and try to get away from the source of the smell. However, their reaction is more intense because their sense of smell is much more powerful than ours.

Ragdoll cat standing on patio next to grass with mouth slightly open

Flehmen Response FAQ

Do humans have the vomeronasal organ?

Yes, humans also have the vomeronasal organ. It is part of the accessory olfactory system, and it is located on the anteroinferior third of the nasal septum. It has specialized olfactory cells, which function as different neurons (which take the information from the nose to the brain). Its function has been linked to the detection of pheromones, but there is extensive research still being conducted on this matter. Another function of the Jacobson’s organ is linked to the production of the gonadotropin-releasing hormone.

Do humans have the flehmen response?

While humans do have the vomeronasal organ, its functionality is still being researched. In fact, there is great debate about this in the scientific community. It has been discovered that even though the organ is present, humans do not display accessory olfactory bulbs that would receive the information from the vomeronasal receptor cells. This suggests that the sensory function of the Jacobson’s organ in humans is non-operative.

Are cats the only animals displaying the flehmen response?

Certainly not; there are plenty of other animals that display this response. In fact, this is a characteristic shared by mammals. If you thought that cats look adorably silly with their mouths open and their eyes popped and fixed, wait till you glimpse other animals doing this, like horses, donkeys, tigers, or even rhinos. However, cats display some of the most developed vomeronasal organs. To give you an idea of their skills, you should know that hound dogs, which are renowned for their keen sense of smell, have 9 receptors in their Jacobson’s organ, while cats have 30 different types of receptors.

Ragdoll cat holding his mouth open after smelling something while standing on tile floor

Clearing the Air About Flehmen’s Response

Is your cat disgusted with you when it has its mouth open?

Is your cat disgusted with you when it has its mouth open?
It is a common misconception among cat owners that cats make the flehmen grimace – yes, it actually has a name – because they are disgusted with a particular smell. There are plenty of jokes about how cats smell their owner’s feet or shoes and then make a surprised face with their mouths open because they cannot stand the smell. As you can see, that is certainly not the case.

Not only are they not disgusted, but when cats use their vomeronasal organ, they are trying to get more information about a specific smell. They are scanning for pheromones. If anything, it should be taken as a compliment. So, the next time you see your kitty with its mouth open and incisors exposed, know it is processing a significant smell. Have you caught your kitty with its mouth open? What were they smelling when you did? Or did you know what they were smelling? Tell us all about your flehmen response stories in the comments section below.

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Hi, I’m Jenny Dean, creator of Floppycats! Ever since my Aunt got the first Ragdoll cat in our family, I have loved the breed. Inspired by my childhood Ragdoll cat, Rags, I created Floppycats to connect, share and inspire other Ragdoll cat lovers around the world,

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  1. Janet Claeys says:

    My girlfriend was leaning over my cat who did the Flehman response. I started laughing and got a puzzled face from my girlfriend. I explained about the response. She was in early menopause. Another time another of my cats did Flehman to same friend. I giggled. She looked and missed it.

  2. My 6 month old Siamese smelled her butt and then made that face, lol ive always wondered what the heck my cats were doing but it makes sense now. Thanks for the knowledge!

  3. ALWAYS a great re-post, Jenny honey! FINALLY experienced Miss PSB exhibiting this behavior since the re-post last year! 🙂 <3

    Big hugs & lots of love & purrs!

    Patti & Miss Pink Sugarbelle 🙂 <3 <3 <3

  4. So glad you re-post this great information, Jenny!! I still haven’t seen Miss PSB display this behavior. Guess she just doesn’t do it for some quirky reason OR we are just bad at noticing it! lol 🙂 <3

    Big hugs & lots of love!!

    Patti & Miss Pink Sugarbelle 🙂 <3

  5. Tyler Romero says:

    My cats do this when they smell my feet… Not regularly anything else but on rare occasion I have seen them do as well although not sure for what. They never do for foreign animal smells (of course they sniffy sniff a lot in the case of other animals but don’t go for the deep smell lol).

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