For curious cat parents
That brief open-mouth, lip-lifted expression has a name: the flehmen response. It is a normal way cats investigate certain chemical scent cues.
A brief flehmen response is normal feline scent behavior and does not by itself indicate disgust.
The response helps direct odor and pheromone information toward the vomeronasal, or Jacobson’s, organ.
Common triggers include scent from other cats, shoes, fabrics, litter areas, and other objects carrying unfamiliar odors.
Your cat sniffs a shoe, blanket, litter area, or unfamiliar object, then pauses with the mouth slightly open and the upper lip raised.
This expression is called the flehmen response. When it is brief and your cat immediately returns to normal behavior, it is generally a normal part of scent investigation.
The cat is using an additional scent-processing pathway rather than simply reacting to a bad smell.
What Is the Flehmen Response in Cats?
The flehmen response is a normal scent behavior. A cat sniffs something interesting, pauses, opens their mouth slightly, and may curl the upper lip. To people, the expression can resemble surprise or disgust even though that is not what the facial posture necessarily means.
Functionally, the behavior allows the cat to process certain odor and pheromone cues through the vomeronasal system.
An open-mouth facial posture
The mouth opens slightly, the upper lip may lift, and the cat pauses briefly after investigating a scent.
Vomeronasal scent processing
The facial posture helps direct chemical scent information toward Jacobson’s organ for additional analysis.
Helpful reference: VCA Animal Hospitals explains that the flehmen response helps pull odors or pheromones toward the vomeronasal organ, also called Jacobson’s organ.
How Does This Weird Cat Face Actually Work?
The ordinary olfactory system and the vomeronasal system process scent information differently. Flehmen is especially associated with chemical cues such as pheromones and hormones from other cats.
During flehmen, the cat holds the mouth slightly open in a way that helps move chemical cues toward the vomeronasal organ in the roof of the mouth. “Smelling with the mouth” is a useful shorthand, but the process involves a specialized sensory organ rather than ordinary taste.
Your cat notices a smell that seems interesting enough to inspect more closely.
They stop moving for a moment and focus on the scent source.
The mouth opens slightly and the upper lip may lift, creating the classic “stinky face.”
Chemical scent cues are directed toward Jacobson’s organ for additional processing.
Helpful reference: VCA Animal Hospitals describes Jacobson’s organ as an additional scent tool that opens into the roof of a cat’s mouth behind the upper incisors.
Common Smells That Trigger the Cat “Stinky Face”
The flehmen response is not a reliable sign that a smell is unpleasant. It is more likely to appear when a scent contains chemical information the cat investigates closely.
Your shoes or socks
Shoes can carry many unfamiliar outdoor odors, including scent from people, surfaces, and other animals.
Another cat’s scent
Scent from another cat can be especially relevant because feline pheromones and other chemical cues are important in cat-to-cat communication.
Blankets, laundry, or beds
Fabric can retain familiar or unfamiliar odors from people, other pets, detergents, and the surrounding environment.
Litter box odors
Urine and other animal odors can carry chemical information. A brief flehmen response near a litter area can therefore occur without indicating a problem by itself.
Catnip, silvervine, or toys
Some cats make the face around enrichment items, especially if the toy holds scent from plants, saliva, or previous play.
PetMD explains that the flehmen response helps cats process pheromones and hormones through the vomeronasal organ, which is why the behavior often appears around animal-related scents.
Usually Normal. But Not Every Open Mouth Is Flehmen.
A brief flehmen response is normal. Open-mouth breathing or panting is different and can indicate respiratory distress in cats. Drooling, coughing, repeated gagging or vomiting, facial pawing, or suspected chemical exposure also deserves attention.
A short pause, open mouth, then your cat goes back to normal behavior.
Open-mouth breathing, panting, labored breathing, or obvious respiratory effort.
Drooling, pawing at the mouth, coughing, gagging, or vomiting.
Strong cleaners, essential oils, sprays, or chemicals can be irritating or unsafe.
Sudden distress, repeated symptoms, or possible toxin exposure should be taken seriously.
What Should You Do When Your Cat Makes That Face?
If the response is brief and your cat returns to normal, you usually do not need to intervene. Let the cat investigate the safe scent source and move on naturally.
Do not punish or scare your cat for sniffing.
Do not shove strong smells toward their face for a reaction.
Store cleaners, concentrated essential oils, and household chemicals securely away from pets.
Keep litter areas clean and avoid relying on heavy fragrance to mask odor.
If the smell is from your shoes
Let your cat investigate briefly, then store shoes away if they keep licking or chewing them.
If the smell is from another pet
Allow calm investigation unless the interaction with the other animal is creating stress or conflict.
If the smell is from the litter box
A brief flehmen response near the litter area can be normal. If the area has persistent odor, focus on removing waste and cleaning the source rather than masking it with fragrance. See How to Eliminate Litter Box Odor for a fuller cleaning routine.
If the smell is on paws or fur
If a harmless substance gets on the coat or paws, use a grooming method appropriate for the material involved. If the substance may be toxic or irritating, prevent grooming and contact a veterinarian or poison-control resource for specific instructions.
Safety note: ASPCA reminds pet parents to be careful with cleaning products and strong household substances around pets, especially cats.
How to Make Your Home More Scent-Friendly for Cats
Scent is an important part of feline communication and environmental recognition. The goal is not to remove every household odor, but to avoid abrupt or potentially harmful scent exposure while keeping important areas clean.
Avoid washing every bed, blanket, and toy at the same time. Cats often like familiar scent on resting areas.
Scratchers and cat enrichment toys can be rotated periodically to vary the indoor environment without changing every resource at once.
Try not to place food, water, sleeping areas, and the litter box too close together.
Avoid unnecessary strong fragrance around key cat resources, and use particular caution with concentrated essential oils because some exposures can be harmful to cats.
Helpful reference: ASPCA Animal Poison Control Center notes that cats can be especially sensitive to essential oils and recommends caution around direct exposure.
The Flehmen Response Is a Normal Part of Feline Scent Processing
The flehmen response is a specialized scent-processing behavior. The unusual facial posture helps the cat direct certain chemical cues toward the vomeronasal organ.
If your cat briefly shows the expression after investigating a shoe, another animal’s scent, or another unfamiliar odor and then behaves normally, there is usually no reason for concern.
FAQs About the Cat Flehmen Response
Why does my cat open their mouth after smelling something?
Your cat may be using the flehmen response. Opening the mouth slightly helps direct chemical scent cues toward Jacobson’s organ, where the vomeronasal system processes information such as pheromones.
Is the flehmen response normal in cats?
Yes. A brief flehmen response is a normal feline behavior. The important distinction is that the cat is not struggling to breathe and returns to normal immediately afterward.
Does the flehmen response mean my cat is disgusted?
No. The facial posture can resemble disgust to people, but flehmen is a scent-processing behavior rather than a reliable sign of that emotion.
Why does my cat make that face after smelling my shoes?
Shoes carry outdoor smells, sweat, other animals, and unfamiliar scent information. To your cat, that can be worth a deeper scent check.
Why does my cat smell something and freeze?
A brief pause can occur while a cat investigates a scent through the vomeronasal system. Freezing that is prolonged or paired with distress should be evaluated differently.
Should I worry if my cat keeps opening their mouth?
A brief flehmen response is normal. Open-mouth breathing or difficulty breathing requires immediate veterinary attention; persistent drooling, coughing, vomiting, facial pawing, or suspected toxin exposure also needs veterinary guidance.
Can strong scents bother cats?
Strong fragrances can alter the cat’s environment, and some products can also be unsafe. Concentrated essential oils and household chemicals require particular caution because risk depends on the product, route, and amount of exposure.
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