Why Do Cats Open Their Mouth After Smelling? (Flehmen Response)

If your cat sniffs something, then pauses with their mouth slightly open like they’re shocked or disgusted, it’s not them “making a face.” It’s usually a normal behaviour called the flehmen response.

In plain terms: your cat is analysing scent in a deeper way than a normal sniff.

What the flehmen response is

The flehmen response is when an animal opens its mouth after smelling something to pull scent chemicals toward a special organ in the roof of the mouth called the vomeronasal organ (also known as Jacobson’s organ). It helps them “read” certain smells more clearly—especially social and territorial scents.

Why cats do it

Cats do this when a smell contains information worth decoding. Common triggers include:

New smells in the home

New bags, shoes, visitors, parcels, or anything that brings unfamiliar scent.

Other cats (or animals) nearby

Outdoor cats often pick up scent marks from other cats in the area and analyse them.

Strong or unusual odours

Perfume, cleaning products, food smells, or anything intense and unfamiliar.

Hormone-related scents

Cats can pick up biological signals that humans don’t notice. This is one reason you’ll see the flehmen response after sniffing certain spots, objects, or even other animals.

Is it bad? Usually no

Most of the time, the flehmen response is completely normal. It’s not a sign your cat is in pain or struggling to breathe. It’s more like they’re “processing data.”

When it could be a problem

The behaviour itself is normal, but you should pay attention if it comes with other signs, such as:

• Repeated open-mouth breathing (not just after a sniff)
• Wheezing, coughing, or noisy breathing
• Drooling, pawing at the mouth, or refusing food
• Sudden lethargy or hiding
• Signs of dental pain (one-sided chewing, bad breath, head shaking)

If you see those, it’s worth a vet check. Open-mouth breathing that looks like panting is not the same thing as flehmen and should be taken seriously.

How to tell flehmen vs panting

Flehmen is usually short and specific: sniff → mouth slightly open → pause → back to normal. Panting looks like sustained open-mouth breathing, often with a stressed posture, and it doesn’t require a sniff trigger.

What you should do when you see it

Most of the time: nothing. Let your cat investigate. If the trigger is a cleaning product or strong scent, reduce it and air the room out. If your cat repeatedly reacts to one specific spot, it may be a scent marker from another cat.

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💭 Final Thoughts

That “funny face” after sniffing is usually your cat using a deeper scent-reading system. It’s normal, common, and nothing to panic about. The only time you treat it seriously is when it’s paired with breathing issues, mouth pain, or other signs of illness.