The Cat’s Mouth Is Half Open! Why?

The expression of cats is often noticed by those who observe their feline companions on a daily basis as they display a range of expressions. Nevertheless, the sudden appearance of a half-open mouth expression in a cat can leave one wondering about the cause, such as if the cat is unwell or if there is another explanation.

✨The cat’s mouth is half open and still!

Dollars are the primary currency used in breathing, so healthy cats rarely breathe through their mouths. However, even these cats may sometimes have their mouth partially open.

Pet owners who are new to owning cats may worry about whether there is a problem with their pet’s health or if there is another reason for this behavior.

There are several reasons for a cat’s mouth being partially open, and I will now discuss them.

❂Causes for a Cat’s Mouth Being Partially Open

If a cat’s mouth is partially open after smelling something, this is considered normal behavior and there is no cause for concern regarding their health.

In most instances, the cat’s eyes will also be droopy during this time. If you have never seen this expression, you may be surprised and wonder what is happening. However, having a partially open mouth after smelling something is a common physiological response in cats called the flehmen response.

Many people may not be familiar with the flehmen response, so let’s take a closer look at this physiological phenomenon.

✨What is a Flehmen response

Earlier, it was stated that a Flehmen response is a physiological reaction to an odor that results in temporarily stiffening with raised lips and a half-open mouth. This reaction is not exclusive to cats, but is also exhibited by other mammals such as horses and cows. While it may appear to humans that the animal is making a silly expression, this behavior is actually quite serious from the animal’s perspective. It should be noted that the expression is not necessarily a result of the odor being unpleasant. Now, we will examine the potential causes of the Flehmen response.

❂Confirming pheromones

The reason behind a cat’s Flehmen response is the analysis of pheromones. Chemical substances produced by animals, pheromones elicit specific behaviors or physiological changes in other individuals of the same species when secreted outside the body.

In regards to cats, pheromones are mainly emitted from the face glands, near the paws and legs, and the anus and provide crucial information about marking and estrus. The detection of these pheromones triggers the Flehmen response in cats.

It is believed that during mating season, sexual pheromones are so subtle and small in molecular size that they often result in a Flehmen response when a cat encounters them in an opposite-sex cat.

Despite their poor vision, cats have a keen sense of smell and gather information from scents by bringing their nose close to the object, rather than relying on visual observations. When two cats first meet, they sniff each other’s nose for information and if the greeting goes well, they will proceed to sniff each other’s tail.

A cat’s sniffing of a nearby pheromone indicates its desire to gather as much information as possible. Even house cats that live alone tend to sniff scents close to pheromones, or slightly open their mouths when feeling their own pheromones in an attempt to gather more information.

If you have observed a cat with its mouth half-open while sniffing its own scent during grooming, it doesn’t mean the cat is making a face because it finds the scent unpleasant. Instead, it is due to the proper meaning behind the Flehmen response.

❂ Confirming Safety

The flehmen response is elicited for a second reason, which is to verify safety.

As gourmet animals, cats possess a keen sense of taste and an olfactory ability that surpasses that of humans by many orders of magnitude.

Therefore, they meticulously inspect their food and possess the capability to determine if it is unspoiled, safe to consume, and free of decay or toxicity by relying on their sense of smell.

In other instances, they may also identify potential dangers by detecting the body odor or excrement of a foe, or by encountering an unfamiliar scent and exhibiting a flehmen response in an attempt to gather more information.

❂ The Mechanism of Flehmen Response

Four-legged creatures such as reptiles, mammals, etc. possess a specialized organ, known as the vomeronasal organ, which serves as a means of detecting pheromones and is distinct from the olfactory epithelium.

Also referred to as the Jacobson’s organ, it is located not in the nose but in the oral cavity near the back of the front teeth, causing the mouth to open halfway to facilitate the intake of odor substances.

This occurs during the act of confirming and is not a prolonged reaction, lasting only a few seconds after the detection of an odor or pheromone.

Therefore, when a cat displays a flehmen response, it is not because they believe it to be a desirable smell, but rather a physiological occurrence that should be respected by avoiding interaction and allowing them to remain at peace.

It is worth mentioning that the vomeronasal organ degenerates in humans during fetal development, making it impossible to exhibit a flehmen response.

❂A smell that easily triggers a phlegm response.

Felines spend a considerable amount of time grooming themselves and a lot of them seem to exhibit a flehmen response when they encounter their own scent. Evaluating their pheromones is also linked to examining their own health, and they may also demonstrate a reaction to secretions from the anal area (anal glands).

In households with numerous cats, they may react differently to the odors of other cats or to cloth-based products (such as their own bed or their owner’s clothes) that contain such odors, thus not all flehmen responses are the result of the same scent.

It appears that they may also exhibit a reaction to their owner’s socks, T-shirts (near the armpits), and tobacco smoke.

✨Even when the same “half-open mouth” is necessary

A partially open mouth in cats is a natural occurrence, however, there are instances where a similar appearance requires attention. In such cases, it is important to determine the cause and take appropriate action to address it.


When a cat is angry and upset, it may partially open its mouth as a threat to its opponent. If the cat is extremely angry, it will reveal its full teeth and make a noise, indicating that it is trying to control its anger before becoming more aggressive. If this behavior is observed during play with the owner, it may indicate that something unpleasant has happened or that the cat is getting excited. To avoid being attacked, it is advised to remain calm and wait for the cat’s emotions to settle.

❂ Mouth breathing

Typically, cats breathe through their nose, but if they are breathing with their mouth partially open, there is a high likelihood that they are having trouble breathing through their nose. If the mouth breathing persists for a prolonged period of time, it may indicate a dangerous condition such as heatstroke or breathing difficulties, so it is important to seek veterinary attention promptly. A normal breathing rate for a cat is 20 to 40 breaths per minute, so if the rate is higher, it is important to visit a veterinary hospital to determine the cause.

❂ Something abnormal in the mouth

If the cat’s breathing is not labored and does not seem painful, but if the mouth is partially open with a painful expression or saliva is drooling or causing discomfort, there may be something abnormal in the mouth. Some common oral problems in cats include stomatitis, periodontal disease, and tumors, which can cause swelling and pain, making it difficult for the cat to close its mouth and causing the mouth to remain partially open. If the cat’s mouth remains partially open even while sleeping, it is suspected to be an oral disease, and immediate veterinary attention should be sought for proper treatment.


It is not uncommon for cat owners to be unaware of what is happening when their feline displays a partially open mouth and a drowsy gaze. This is known as a flehmen response, which is a natural physiological occurrence in quadrupeds, including cats, and does not indicate a problem. However, if the partial opening of the mouth is not a result of the flehmen response, it is crucial to determine the cause and take immediate action.

If the cat appears angry or threatening, it is advisable to avoid further stimulation, and if there are issues with breathing or abnormalities in the oral cavity, it is important to seek veterinary treatment promptly.

While cats may look adorable with partially open mouths, it is important for their owners to be able to recognize and distinguish between a harmless and a dangerous partial opening by closely monitoring their behavior on a daily basis.

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