Why Do Cats Hold Their Mouths Open After Smelling Something?

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Originally published May 5, 2016

cat flehmen response
Caymus after smelling Trigg’s butt. Gross. April 17, 2010

My childhood Ragdoll cat, Rags used leave his mouth open after he would smell things quite frequently, and I came to hate it because it was often after smelling urine or another cat’s butt.  But, when I found out what he was doing, I thought it was pretty rad.

You know what I am talking about – where they leave their mouth slightly open and then sort of daze off for a second and then lick their nose and close their 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 and I

Flehmen Reaction in Cats
Caymus still taking it in. April 17, 2010

couldn’t figure out why until later when I had stopped by my parents house and Caymus couldn’t leave me alone either – Caymus never shows attention like that, so I knew I had something on me.  Came to find out that the recycle bin had been sprayed by a male cat and I had the smell of urine on my pants – LOVELY.

So when I came home, I immediately changed out of my

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

pants and had Charlie and Trigg give them a good whiff, so that I could get a photo for this post!

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

The act of opening the mouth and drawing up the air to the Jacobson’s organ is called the “flehmen reaction”.

Charlie using his Jacobson's organ
Charlie using his Jacobson’s organ

Essentially, the cat is opening her mouth to suck in the air into the Jacobson’s organ and take a really deep sniff of the odor.

Charlie's flehmen reaction
Charlie’s flehmen reaction

This special sensory organ called the vomeronasal organ or Jacobson’s organ allows a cat to have 14 times the sense of smell of a human.  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 their mouth behind their teeth.

The reason they look dazed for a second or two is 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

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

secrete pheromones, which are chemical substances that stimulate a behavioral response, such as an avoidance or aggressive reaction. Pheromones are also found in saliva, feces, and urine. When cats “spray” it’s another way they are marking territory.

More About the Flehmen Response

It is a well-known fact that cats have a much keener sense of smell than us humans do, but how they manage to out-sniff us is not common 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 certain smell.

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 very important they only breathe in through their mouths. In fact, this is one of the reasons why they make that odd face. 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 something 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 certain 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 huge role in interspecies communication.

The vomeronasal organ is olfactory-chemosensory organ which 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.

The flehmen response is much stronger in males, which have to be particularly perceptive of the pheromones of females in heat, but also to those of other males. This plays a very important 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. In households with more than one cat, they can be seen displaying the grimace more often.

Moreover, keep in mind that you bring in new smells in the house from outside every single 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.

On the roof of the cat’s mouth, just behind its incisors, you can see two openings. These are the openings to the nasopalatine canals, which are filled with fluid. This makes it impossible for the smell to go up passively from the mouth to the nose.

For 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.

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

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 afferent 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, then wait till you get a glimpse of other animals 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.

Clearing the Air About Flehmen’s Response

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 certain smell. There are plenty of jokes about how cats smell their owner’s feet or shoes and then make the surprised face with their mouths open because they simply cannot stand the smell.

As you can see, that is certainly not the case. Not only are they nor disgusted, but when cats use their vomeronasal organ, it means that they are trying to get more information about a certain smell. They are essentially 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 that it is processing a very important smell. Have you caught your kitty with his or her 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.

Comments (32)

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  1. Ha, this is perfectly timed, I just explained recently to my husband about this phenomenon……our kitties only do it when they smell something gross, but it is so funny to see them doing it! I will try to get a picture next time 🙂

  2. That’s a very common behavior for kitties! They do it anytime they smell something exceptionally interesting and/or new…the opening of the organ allows them to truly “savor” the scent. I think it is adorable! Raina doesn’t do it so much but will on occasion make her “funny face” when I come back after visiting new cats. 🙂

  3. Thank you for that imformation on the cats smelling senses. I was always wondering what exactly was making them do that..They always get this strange look on their face kind of creepy sometimes..Horses do the same kind of thing but curl their top lip and head way up….Critters are so funny sometimes…

  4. Thank you so much for this explanation. My new kitten was just doing this when I was trying to eat some pineapple. He came up to me being very curious of course and so I showed him a piece. He sniffed it through the nose, but then I saw him suddenly sit up, open the mouth, and yes have that daze of stupor. It was cute, but I was like, “What are you doing?” I literally thought for a moment that he had licked it and it was just too tart or acidic for his little tongue =) Thanks again!

  5. Okay I have a couple of photos =) And apparently interesting stories.
    My kitten does that thing with his mouth with anything new he is smelling. He was smelling my clean laundry that I placed on my bed to fold and he made that face:

    http://i114.photobucket.com/albums/n271/Dew_Dust/010.jpg

    And he was smelling a banana peel and opened his mouth and went into that weird stare:

    http://i114.photobucket.com/albums/n271/Dew_Dust/015.jpg

    I assure you there was no urine on the clothes that came out from the dryer or on the banana peel =D

  6. Very interesting. A lot of other animals and reptiles do this as well, from horses to snakes. It’s also part of why cats and dogs cope much better with blindness than humans – their other senses (including smell) are so much more actue. Apparently scientists did a study and found that blind cats with whiskers, where better at catching mice than sighted cats with no whiskers (I assume they must have been good mousers to start with! )
    Grace x

  7. Hey, my cat does this when she licks my face (usually the bridge of my nose, my eye lid or cheek). It’s a loving gesture.. but I DEFINITELY don’t have urine on my face!!
    Any thoughts??

  8. I knew the Jacobson organ thing, and thought it was really interesting. Then my friend Demian started calling it “ass face,” and that’s all she wrote. Now the only way I can remember the real name is when I look it up online. For ever more, it will be known in my house as, “Oh, look! Diamond has ass face!” Classy,I know.

  9. Fascinating post, Jenny! I have never noticed this in any of the cats we’ve had (and neither has my hubby)…probably because we weren’t paying close enough attention. You can betcha I’ll be watching for this now, though! So very interesting! Thanks for the great info on this behavior!!! 🙂 <3

    Big hugs!

    Patti & Miss Pink Sugarbelle 🙂 <3

  10. Love to see this reaction on my girls. Happens when we’ve been out to the zoo sometimes. I purposely let them take a whiff and they get that reaction. So funny! Wish I could smell what they smell sometimes, but most of the time, am pretty glad that I can’t! Thanks for the interesting post!♥♥♥

  11. Very interesting! Isabella has a shoe fetish and does this whenever anyone takes off their shoes. She stuffs her head into their shoes and then she comes up for air like it was really bad in there! I always give my sister a bad time…maybe I won’t tell her the REAL reason Isabella does this! 🙂

  12. We have a have a set of male & female siblings at home. We always thought that it looks like they’re “smiling” when they leave their mouth open after smelling something they liked!
    Romeo & Juliette are more likely to “smile” right after my husband comes home from work & gives them a quick pet coming in the door…. it’s not just his hands, but his shoes as well that makes them go in for a sniff & a grin. (He’s a chef & comes home smelling like food before he showers!
    I -KNOW- it CAN’T POSSIBLY be urine, or another cat they’re reacting to.

    Is it possible that they do it with smells they find pleasant? Not just other cats?
    -Robyn

  13. Molly does that quite often. In the case of her doing it when she sniffs our domestic shorthair’s posterior, I think she may be smelling a disease, but maybe not. Jenny (our domestic short hair, not you dear) is very old and losing weight, so I don’t think she’ll be with us much longer. Randy and I went to Gold Rush days in Old Sacramento back on Labor
    Day weekend. When we got home (they have horses and wagons on the street just like the old west), Miss Molly went bonkers sniffing our shoes. I think she could quite literally smell the horses (and no, I didn’t have any horse apples on my shoes). I told Randy she was ‘reading the newspaper’.

  14. Such a great post, Jenny! So glad you re-posted this one! I still haven’t noticed this happening with Miss PSB yet. Guess I really need to get out more and get more interesting smells on me or something! I’ll definitely continue to keep an eye out thought and if I can catch her doing it and take a photo of it (a longshot with my photographic skills), I’ll send the photo to you. 🙂 <3

    Big hugs & lots of love!

    Patti & Miss Pink Sugarbelle 🙂 <3

  15. 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).

  16. 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

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