Why Does My Cat's Mouth Hang Open?
Our elegant feline friends usually keep their mouths shut. A cat that opens his or her mouth for no apparent reason is a sight that alarms an attentive owner - sometimes with good reason! Why is Kitty’s mouth hanging open? It could be a harmless form of behavior called "the Flehmen reaction" or it could be something to discuss with your vet. Let's review the options together in this article.

Cats normally breathe through their noses. When a cat opens his or her mouth it’s usually for something specific such as eating, drinking, grooming or vocalizing. Or possibly even biting an annoying someone or to chew on something. As human beings, we find all of these easy enough to understand.

In fact, there is one more harmless and perfectly natural reason for a cat to sit there, mouth hanging open: the Flehmen reaction.

What’s the Flehmen reaction?


The Flehmen reaction or Flehmen response is a behavior unique to certain mammals - including cats. When a cat notices an interesting smell he or she will sometimes open their mouth for a more thorough prolonged sniff. Taking air in through the mouth allows the cat to analyse it using a special organ that’s known as the Jacobson’s organ or the vomeronasal organ.

The cat’s Jacobson’s organ is located in the upper jaw, above the roof of the mouth. A very small duct takes the air into this specialized organ where the cat can study the sample.

In a way, your cat has a sense that’s a combination of taste and smell! Kitty can literally use his or her mouth to "taste smell"!

What does the Flehmen reaction in cats look like?


A cat comes across an interesting smell. After some intensive sniffing, he or she will usually stop, open his or her mouth a little and take a few seconds to ponder. This is often followed by a distinct facial expression. Some owners read that as “Ewwww, what’s that smell!” and it can be funny to watch (especially when triggered by sniffing another cat’s behind!)

Here’s a nice example of a calico cat investigating a special scent on a blanket -

And another cat discovering something invisible yet clearly fascinating on a table -

When does the Flehmen reaction occur?


Scientists believe that the Flehmen reaction is triggered by certain pheromones. Pheromones are chemicals that animals and plants use as a form of invisible silent communication. A cat secretes pheromones that can tell other cats quite a lot. These messages can tell whether or not a cat is available for mating or is aggressive and dominant. Whatever the message, it must be very interesting, judging by the reaction!

We know that some animals respond to pheromones secreted by a different species. No one knows for sure if this is an elaborate communication mechanism between species or perhaps these pheromones are just too similar and confusing. We do know cats often respond to pheromones left by dogs and even humans!

This hilarious video compilation shows how cats interact with human feet. The pheromones we secrete from our feet apparently trigger a Flehmen reaction in cats -

Could there be a different reason why my cat’s mouth hangs open?


The Flehmen reaction is harmless and can even be funny to watch. However, there can be other reasons for a cat to keep his or her mouth open. Some cats seem to forget themselves for a second or two during grooming, staring at something with their mouth slightly ajar. They may even close their mouth… and leave the tongue hanging out there!
Cat with its tongue hanging out - a common sight that doesn't indicate a problem, just a silly cat!

Health problems that can leave a cat with his/her mouth hanging open


If your cat keeps his or her mouth open for longer than a few seconds at a time and appears to be breathing through the mouth, this could indicate a medical problem.

Several medical conditions can make a cat’s nose partially or totally blocked, to the point of forcing the animal to breathe through its mouth. These conditions include -
  • A bacterial or viral infection
  • Allergies
  • Tumors in the nasal cavity
Other times, the nose is fine but the cat's mouth hurts. Stomatitis and gingivitis in cats are diseases of the mouth that can be very painful.

Read more: Gingivitis And Stomatitis In Cats

Talk to your vet if you notice that your cat constantly keeps his or her mouth open. Mention any other symptoms which could indicate a problem, especially -
  • Swelling in or around the face
  • Loss of appetite
  • Fever
  • Lethargy or excessive sleeping
  • Any change in the cat’s behavior patterns
Learn more: 35 Signs that Your Cat May Be In Pain

What to do if your cat begins to pant?


Panting means your cat is experiencing respiratory distress. This can sometimes happen when a cat is extremely stressed out, but it can also be a sign of serious medical conditions. You may see the following -
  • Panting and difficulty breathing
  • Lowered head with elbows pulled away from the body
  • Apathy and refusing to move
  • Coughing
  • Bluish gums (indicating low levels of blood oxygen)
These are all signs that your cat is literally struggling for air and may need immediate oxygen supplementation. Remain calm and try to keep the cat calm,too, as stress could make things worse. Gently place the cat in a carrier and rush him or her to the vet.

What could be the cause of panting in cats?


Acute respiratory distress in cats is fortunately a rare occurrence, and you will probably never see it. Common causes include -
  • Heart disease in cats which leads to fluid accumulation in the lungs
  • Any disease which affects the lungs
  • Trauma (injury) to the cat’s chest
  • FIP (Feline Infectious Peritonitis) which can lead to fluid accumulation in the stomach and chest, preventing the lungs from filling properly.
Always be prepared for a medical emergency and know where to turn if it happens. If your veterinarian doesn’t offer a 24/7 service ask him or her in advance where you should turn in case of emergency. Have a carrier ready and a way to get to the vet.

Still not sure why your cat’s mouth is hanging open?


If you noticed the signs of a medical problem, stop reading now and call your vet.

Otherwise, talk to us! Try to capture a video of your cat with his or her mouth hanging open and post it in the cat forums where experienced cat owners may be able to help you identify a Flehmen reaction or suggest another explanation!