Why Do Cats Open Their Mouth When They Smell?

People often interpret this action as disgust. A cat that is wrinkling its nose, pulling back its upper lip, and leaving its mouth hanging open looks like a human when they smell something gross.

But cat anatomy and behavior are different from ours. The phenomenon of cats opening their mouths when sniffing has nothing to do with repulsion and can be explained scientifically.

Learning why cats open their mouths when sniffing something can help you not solely surprise friends with new facts but also better understand your pet.

Flehmen Reaction

Cats aren’t the only animals that open their mouths when sniffing something. This phenomenon is known as the flehmen response and occurs in many species, including horses, tigers, zebras, dogs, and tapirs.

“Flehmen” isn’t the last name of some scientist. The name of this phenomenon is derived from the Upper Saxon German word “flemmen,” meaning “to look spiteful,” or from German “flehmen,” translated as “to bare the upper teeth.”

When you know the word’s etymology, the name of this odd reaction to sniffing becomes reasonable. Cats expose their upper teeth when smelling something, although this physiological response is more apparent in horses due to the anatomy of their teeth.

The phenomenon was first described back in the early 19th century by Danish surgeon Ludwig Jacobson. The Jacobson’s organ that sucks in air when a cat sniffs something acquired its name from the same scientist.

We should first learn the feline olfactory organ anatomy to understand how flehmen reaction works. Like many other mammals, cats have an olfactory organ called the Jacobson’s organ, located just above the roof of the mouth, in the nasal cavity.

Some humans may have physical remnants of this organ from our ancestors, but it’s non-functional. The organ became redundant because we don’t need to analyze as many smells as our ancestors – imagine how we would look if we had to expose our teeth when sniffing.

If you open your cat’s mouth, you can notice two tiny ducts on the roof of its mouth – these are nasopalatine canals connected to the said organ. However, you better trust our word and don’t attempt to open your cat’s mouth by force.

The nasopalatine canals are filled with saliva that transmits smell molecules up to the vomeronasal organ with special muscles, where these molecules are identified.

Scientists suggest that Jacobson’s organ processes a different kind of information than the human nose. Perhaps, the information processed by Jacobson’s organ during the flehmen response lies between smell and taste.

But why do cats require a spare form of sniffing? Can’t they sniff without opening their mouths? Felines can use the primary form of sniffing in some situations, but when they need an in-depth scent analysis, they implement the flehmen response.

The average tabby cat has nearly 30 types of smell receptors, whereas hound dogs have only nine. The more receptors, the more scents animal can distinguish.

If you think that 30 is a lot, you may be surprised that mice have hundreds of scent receptors to recognize every mouse in their social circle.

Cats need so many receptors for the same reason – to distinguish between family and enemies. Studies have shown that animals primarily use the flehmen response when investigating smells of their species.

The flehmen response in cats is an essential tool of intra-species communication, facilitating reproduction and post-partum recognition. In simple terms, this response enables felines to identify another cat’s reproductive status and their kittens.

For this reason, you will rarely see a cat opening its mouth when sniffing food or humans but often when a cat is sniffing another cat’s urine.

Think of it as of high-resolution sense of smell. While we see a blurry picture of a creature with four legs, a cat can precisely identify the cat’s age, sex, and health state.

This doesn’t mean a cat can’t implement the flehmen response when sniffing an unfamiliar person, for example. If your cat opens its mouth when sniffing socks, the reason likely isn’t an unpleasant sweat odor but an interest in where you’ve been.

Pheromones

The scent molecules that help cats read information about other felines are called pheromones. The word “pheromones” is derived from the Greek for “to carry” and “to stimulate” – “pherin” and “horman.”

These chemicals are synthesized in various places in the feline body, including cheeks, under the chin, paw pads, urine, anal glands, and skin.

When a cat rubs its face against something, it releases pheromones to communicate with other cats. Pheromones differ – some are meant to attract mating partners, whereas others are used to mark individuals within a cat’s social group.

So, when your cat rubs its cheek against you or headbutts you, it marks you as part of the family. But cats can’t detect pheromones using their nose. They can only read information from pheromones using Jacobson’s organ.

That’s why your cat opens its mouth when sniffing another cat’s tail or pee. Some people interpret this reaction as disgust or aggression, but the cat is simply analyzing pheromones.

Cats can also analyze human hormones using Jacobson’s organ. For example, when a woman is pregnant, her body releases high levels of progesterone and estrogen. Cats can sense this change even before the woman finds out about her pregnancy.

So, if your cat opens its mouth when smelling you, it isn’t disgusted but may be analyzing your hormones.

Unpleasant Odor

People often think that cats open their mouths when sniffing something repulsive. People can make a face similar to the flehmen response when sensing a foul odor, but the response depends on how interesting the smell is rather than how pleasant it is.

Furthermore, cats don’t always share our opinions about smells. We may perceive decaying fish or cat pee as absolutely repulsive, but the same scent can be utterly fascinating for a cat.

In contrast, when cats smell something they find disgusting, such as citrus or nail polish remover, they don’t typically open their mouth but leave the source of the scent quickly.

The Blep

In case you’re unfamiliar with “blepping,” it’s a meme name for when cats poke their tongue out of their mouth. Sometimes, cats do “the blep” after sniffing something, but not necessarily.

A cat that has smelled something interesting and activated its flehmen response may be so distracted by the investigation that it forgets to pop the tongue back into the mouth.

Blepping is also common when a cat is trying to focus on a new flavor – for example, when you give your cat a new treat. In this case, the tongue sticking out serves two purposes: analyzing the taste and activating the flehmen response.

Sometimes, cats leave their tongue out after sniffing something because they get distracted by a sudden noise. Either way, a cat’s tongue sticking out when sniffing is perfectly normal and doesn’t require veterinary attention.

Stress, Heat, & Other Reasons

The flehmen response and “the blep” can be easily confused with panting due to overheating or respiratory issues. Unlike dogs, cats don’t typically breathe with their mouths open.

The only scenario when panting for a cat is normal is following a vigorous exercise because it helps a cat regulate its body temperature. But you should be concerned if your cat hangs its mouth open for no apparent reason.

Cats opening their mouths because of flehmen response only do it for a short time. If your cat keeps its mouth open for long and the air temperature is high, your pet may be overheating.

Watch out for other signs of overheating, including rapid breathing, red tongue, staggering and stumbling, lethargy, and reluctance to eat. Sometimes, cats with a heat stroke vomit.

Another common cause of a cat keeping its mouth open is stress. When stressed, cats need more oxygen to calm down and instinctively open their mouths.

Sometimes, anxiety in cats is triggered by a new scent, usually the scent of an unfamiliar animal. A cat may also keep its mouth open after smelling or licking a toxic substance.

Some substances are so toxic to felines that they can cause poisoning even when inhaled. If your cat starts drooling, coughing, vomiting, or breathing rapidly after sniffing pesticides or household chemicals, seek urgent veterinary help.

Do Cats Always Open Their Mouths When Sniffing?

Cats don’t always activate their Jacobson’s organ when sniffing. Although the flehmen response helps felines analyze scents better, they can smell just fine with their nose.

A cat’s nasal cavity is lined with a mucociliary blanket that contains nerves and cilia. When scent molecules enter the nasal cavity, they are dissolved in the mucus lining and bind to olfactory neurons that analyze the smell.

In other words, your cat smells its surroundings constantly because felines are curious creatures. But when cats need to analyze another cat’s pheromones, human hormones, or a new flavor, they additionally use the flehmen response.

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