Why Does Your Cat Leave Its Mouth Open While Sniffing?


Being the curious animals that they are, cats love to investigate just about anything they can find. Cats are able to notice their surroundings and learn more about other animals or objects thought their incredible sense of smell. Have you ever noticed that occasionally, after some intensive sniffling, your cat may stop, open his or her mouth a little to ponder, as though it’s in a trace? It may wrinkle its nose and draw back its upper lip, something us humans may think is a negative reaction to a disgusting smell. But what exactly is your cat doing? Is it really disgusted by the smell, is it a medical condition or is it just something else entirely? 

Flehmen Reaction

Although unnerving to see first thing in the morning, it can be a normal behavior for cats called the “Flehmen Reaction”. Cats have an organ on the roof of their mouths that allows them to analyze scents called the vomeronasal organ, or Jacobson’s organ. To gain access to it, they need to open their mouths and promote airflow across the vomeronasal gland, allowing the organ to process the scent more deeply than your nose can and send signals to your cat’s brain. This sense is a combination of taste and smell. In fact, this organ allows your cat’s sense of smell to be 14 times more intense than us humans.

What triggers this reaction to occur?

The Jacobson’s organ processes scents that are called pheromones. It’s highly likely that your cat only makes this weird sniffing face occasionally when it smells other cat’s faeces, urine or when sniffing certain parts of your home. These are usually times when your cat is trying to pick up pheromones. Pheromones are chemical substances that animal secretes to other animals in its species, and this includes cats. Pheromones are secreted through glands on a cat’s face, paws and anus to mark their territory or leave indicators for other scents. Other ways cats can use the flehmen response include:


  1. Marking territory and or identification

Unneutered male cats commonly use urine to mark their territory. A household with multiple unneutered male cats may result in the cats likely urinating around the house. This is an attempt to mark their territory from other cats as urine has pheromones in it, which are unique identifiers that tell other cats their age, gender, and other factors. Have you ever noticed your cat rubbing their faces on furniture or objects? Well, they’re marking them with their pheromones, which indicate feelings of calm and familiarity. Cats may also scratch on things to leave pheromones from their paws. Cats then use the Jacobson’s organ to analyze these scents to determine whose territory it’s walking on, and they may feel welcomed or threatened there based on that information.

  1. Locating a female cat in heat

Male cats often use the flehmen reaction to pick up on pheromones from female cats who are in heat to mate with. Female cats that are in heat releases pheromones as a signal for males in the area to draw near and telling them that she is ready to breed. A male cat will then use his flehmen response to get a better idea of who the signal belongs to and understand where the female cat is located. Once the female has gotten pregnant, she will stop releasing these pheromones. However, sprayed cats don’t release these mating signals since they can no longer be in heat.

  1. A mother cat keeping track of her kittens

Mother cats use pheromones to identify and track their kittens. The mother’s milk also releases pheromones to calm agitated kittens down and work as a guide for kittens to find each other and their mother. For example, a kitten may accidentally stray from the litter and get lost. By remembering the pheromones in its mother’s milk, it can follow that trail back to its hiding spot.

  1. Responding to food or catnip

A cat will use the flehmen response if a meal is too far away or the cat isn’t sure about it. A cat may also open its mouth to sense it if it’s particularly enticed by the odor, especially for catnip as they may interpret the catnip as feline pheromones. However, some cats may be aggressive or be playful to the catnip depending on its personality and biology. For cats that have a positive reaction to catnip, it can help relieve anxiety and even pain.


Other reasons your cat’s mouth hangs open

There may be cases where it indicates dental pain or health issues. An open mouth may indicate a medical problem if your cat keeps its mouth open for longer than a few seconds at a time and appears to be breathing through the mouth, such as its nose being partially or totally blocked. If this is the case, your cat will be very stressed and you will see it struggle to breathe, taking deeper breaths and may even appear frantic. Some conditions that cause this includes:

  • Bacterial or viral infection
  • Allergies
  • Tumors in the nasal cavity
  • Heart or lung disease
  • Feline Infectious Peritonitis (FIP)
  • An injury to the cat’s chest


Sometimes it’s the mouth that is hurting instead of the nose. Stomatitis and gingivitis are common mouth diseases that can be very painful. Cats with inflamed gums or teeth will open their mouths to limit discomfort. In these cases, you’ll have other clear symptoms that warn you about what’s happening especially

  • Swelling in or around the face
  • Loss of appetite
  • Fever
  • Lethargy or excessive sleeping
  • Any change in the cat’s behavior patterns 


A cat may also open its mouth when they are preparing to bite. An open mouth could be a warning for you to stop something, especially if you are petting your cat when this happens as it is a clear indicator that the cat isn’t having fun anymore. Give it space until it relaxes or calms down. Other signs of aggression that may indicate your cat is about to bite includes:

  • Fidgeting
  • Tensing
  • Growling
  • Hissing



While a cat holding its mouth open is a normal occurrence, it is important to ensure that it is not matched with symptoms of health issues as indicated above. Pay close attention to your cat and allow your cat some space if it seems agitated to prevent unwanted biting.


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