Why Do Cats Open Their Mouth When They Smell?

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Cats are famously known as animal species forever curious about their immediate surroundings. They try to satisfy their curious instincts by sniffing everything close to their visual periphery. Their strong sense of smell helps them navigate toward the object or food that has caught their attention.

However, if you are a cat lover or an acute observer, you must have noticed that cats scrunch their nose and leave their mouths open for a few seconds after smelling something. A cat’s weird face after smelling something is termed the flehmen response, or in layman’s terms, the “stinky face.

This article will briefly discuss the definition of flehmen response and why cats tend to make the “stinky face.”

Why do Cats Open Their Mouth When They Smell?

The flehmen reaction is the term used to describe the open-mouth breathing of cats while smelling something. Flehmen’s response is witnessed in several animals, including the cats. These animals have special scent receptors on the roof of their mouth and nose.

Dutch anatomist Frederick Ruysch, in the 1600s, studied the vomeronasal organ, also called Jacobson’s organ. This is where these scent receptors are located. The presence of these receptors on the roof of the mouth and nose leads these animals to open-mouth breathing, later termed the flehmen response. In its literal definition, the name means “to bare the upper teeth.”  This is because animals exhibiting flehmen response curl back their upper lip, exposing their front teeth while inhaling with their nostrils.

Cats exhibit the flehmen response when they identify an unfamiliar and interesting scent. The scent then travels to the vomeronasal organ, where the sensory cells lie.

The Vomeronasal Organ in Cats

As stated earlier, the vomeronasal organ is a special cat gland with sensory receptors. The organ rests on the roof of the mouth and consists of ducts leading to the mouth and nose. The primary function of the Vomeronasal Organ is to detect the pheromones secreted by other cats.

The secreted scent is collected in the mouth. This is when the cats make a stinky or grimacing face. The cat curls up its upper lip and partially opens its mouth for a few seconds. This expression is given the name flehmen reaction.

As cats urinate to mark their territory, cat owners often find it revolting and irritating to find the smell of urine everywhere. Stress is another main reason that prompts cats to pee, claw, scratch, and damage furniture. So, the best way to keep a cat calm is by purchasing the FELIWAY Optimum Pheromone Diffuser. It is a high-rated product that helps in reducing the most common signs of stress in cats. Its calming effect helps the cat feel more comfortable and relaxed.

What Smells Trigger Flehmen Reaction in Cats?

Cats do not make the “stinky face” all the time. They scrunch their nose only when smelling certain scents. The prominent scent that triggers their sensory receptors is called pheromones. These are chemical substances often released by animals to communicate with one another. Cats secrete pheromones through glands in their face, paws, and anus.

The table below lists the common types of smell that triggers the flehmen reaction in cats.

Gender of the CatThe Kind of Scent That Triggers Cats
Male Pheromones in the urine or feces used to mark the territory
MaleThe scent of female cats who are in heat
MaleOdor in the urine or feces to determine the presence of other male cats in the area
FemaleThe smell of kittens tracks them down

Flehmen Reaction in Male vs. Female Cats

Numerous pieces of research have predicted that male cats experience the flehmen reaction compared to female cats. This is because male cats constantly guard their territory and are forever hunting for other male intruders. The scent from the pheromones of these intruders helps the cats track them down to ensure the safeguarding of their area. The pheromones also help the male cats track down female cats in heat.

However, female cats also experience the flehmen reaction, but it is mainly restricted to tracking down their kids.

Is Flehmen Reaction a Cause of Worry in Cats?

No, the Flehmen reaction is not a cause of worry in cats. It is a natural and normal response of a cat to detect an unfamiliar or interesting smell. However, if you are a cat owner, it is essential to note that you distinguish other similar signs of your cat from the flehmen response.

Panting or open-mouth breathing is one such sign that projects that your cat might be suffering from asthma or respiratory distress. Panting can also signify heat exhaustion, heat stroke, and cat poisoning. In such cases, you must take your cat to the vet for immediate treatment.


Like humans, animals also have unique ways of responding to unfamiliar smells. Cats do so by making a weird expression that gives the appearance of a grimacing face. However, this is nothing to be worried about as it is a natural reaction to the scent of pheromones.

Thus, next time you see a cat smelling and making a weird face, remember that this furry friend is hellbound in investigating its surrounding with its strong sensory receptors.

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