The Fascinating Flehmen Response in Cats

Observe: Your cat crouches with his nose down, nuzzling the ground, before glancing up with his mouth slightly (and comically) open. So, why do cats open their mouths after smelling something? It turns out this is a behavior called the flehmen response. Let’s dive into what this intriguing response is all about!

Why Do Cats Open Their Mouths When They Smell Something?

Although it may appear that your cat is staring in open-mouthed disbelief, there’s actually a reason behind this funny face: Your cat is analyzing a new or strange smell—but instead of sniffing through the nostrils, he is “scent-sucking” through the roof of his mouth.

This behavior is known as the flehmen response.

Brown and white tabby with mouth open - flehmen response in cats

Understanding the Flehmen Response in Cats

Anthrozoologist John Bradshaw explains that the flehmen response opens up two small ducts on the roof of your cat’s mouth behind the incisors. This allows the scent to travel to the vomeronasal organ, also called Jacobson’s organ, on the roof of the mouth.

According to Dr. Sasha Gibbons of Just Cats Veterinary Hospital in Stamford, Connecticut, “Cats use the flehmen response to detect chemical stimuli, such as pheromones, that are present in urine and feces, or areas that cats have marked with scent glands.”

The flehmen response is a voluntary action and is considered a sense that lies somewhere between smell and taste.

Male Cats vs. Female Cats

According to Dr. Gibbons, male cats are more likely to exhibit the flehmen response in relation to mating. On the other hand, female cats may use it to keep track of their kittens.

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Of course, neutered male cats and spayed female cats are likely to display the flehmen response even without mating or kittens on their minds. The smell of cat urine and other pheromones is most likely to trigger this response. Another surprising trigger for your spayed or neutered cat’s giggle-inducing sneer? Catnip! Catnip produces a chemical response in a cat’s brain when inhaled or ingested.

Female lion with mouth open - flehmen response

Other Animals That Exhibit the Flehmen Response

Cats are just one of many animals that exhibit the flehmen response. Dogs, camels, llamas, goats, horses, tapirs, rhinos, rams, elk, giraffes, buffalos, hedgehogs, and more also display this behavior. Even your cat’s wild relatives—lions and tigers—show this behavior!

Contrary to popular belief, cats actually have a stronger flehmen response compared to dogs, despite dogs having a superior sense of smell. According to Bradshaw, the average tabby has 30 different types of receptors in the vomeronasal organ, while a hound dog has just 9.

Once upon a time, humans may have had the flehmen response too. However, evidence of the vomeronasal organ is only seen during human fetal development. After birth, “the only remaining clues are a pair of pits at the bottom of our nostrils where the ducts used to connect to the organ.”

Don’t Confuse the Flehmen Response in Cats for Open-Mouth Breathing

The flehmen response in cats is absolutely normal and nothing to worry about. However, it’s important not to confuse it with other signs that may indicate respiratory distress or health issues in your cat.

Panting or open-mouth breathing could be a sign that your cat has asthma or is experiencing respiratory distress. If you notice these symptoms consistently or a respiratory rate of over 50 breaths/minute, it’s best to call your vet or make a trip to the emergency clinic. You can easily measure the respiratory rate by counting the number of breaths in 15 seconds and multiplying it by 4.

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Panting may also indicate heat exhaustion or heat stroke in cats. Additionally, it can be a sign of poisoning, such as after consuming garlic or onion or being exposed to harmful essential oils. Lastly, panting after playing may be a sign of hyperthyroidism in cats.

When in doubt, it’s always a good idea to consult your veterinarian or head to an emergency clinic to get your cat checked out!

Goat with mouth open - flehmen response

The More You Know

So, now you know why your cat makes that funny open-mouth face after smelling something. Spread the knowledge: The flehmen response in cats (and many other animals) is an intriguing factoid that you can impress other pet parents with!


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Photo by Ariana Suarez on Unsplash

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