Discover Why Cats Open Their Mouth When They Smell

Domestic cats are very common pets in many parts of the world. These small felines have a variety of unique behaviors, like using their owners’ furniture as a scratching post, running through the house at 3 a.m., and more. Cats also tend to freeze up, open their mouths, and make funny faces when they smell something unique. Learn why cats open their mouth when they smell, including the biological function it serves, and why it is nothing to worry about.  

How Well Can Cats Smell Compared to Other Animals?

Before we look at why cats always open their mouth when they smell, let’s take a look at how well they can smell in general. While their sense of smell is not as potent as some types of dogs, cats can still sense smells from upwards of 4 miles away in the right conditions.  

Another facet of how well cats smell is a matter of context. Humans have roughly 5 million olfactory receptors in their noses. Meanwhile, cats have somewhere between 40 and 200 million scent receptors in their noses. Some sources claim that they have even more of these receptors. Also, cats have more vomeronasal receptors (V1R receptors) than certain types of dogs. These receptors help animals pick up on pheromones from other animals using their vomeronasal organ, also called Jacobson’s organ.

So, cats have a much more powerful sense of smell than humans and a less powerful ability to smell than some sorts of domestic dogs. However, some studies suggest that cats are better at discerning between various smells than dogs.

Now that we understand a little bit about a domestic cat’s sense of smell, we can explore the reason behind them opening their mouths when they smell.  

Why Cats Open Their Mouth When They Smell

Cats open their mouth when they smell because they are trying to get more information from the odor stimuli by engaging the flehmen response. The flehmen response is when an animal keeps its mouth open while smelling something, almost looking as though it is sensing a foul odor. Cats will often hold their position and inhale with their mouths open when using this response.  

Now, that may seem odd because we imagine that cats would just take an extra-large sniff rather than keep their mouths open. However, cats, along with many other animals, have a vomeronasal organ, also called Jacobson’s organ.

This organ is above the roof of the cat’s mouth, so they breathe in through their mouth when engaging the flehmen response. The vomeronasal organ helps the cat sift through the scent and pick up other distinctions that their nose alone would miss out on.

Cats using this organ can help them glean more information from certain odors, identify pheromones, sense a sexual partner’s readiness to mate, and more.

So, the next time you see a cat making a “stinkface”, they’re just trying to get a better sense of what’s around them.

What Does the Flehmen Response Look Like?

Cats will make what some people call a “stinkface” when they’re engaging the flehmen response. A cat will open its mouth, curl its tongue, and sometimes curl their upper lip to expose their teeth. These mammals may also look like they are confused, scared, or grossed out as well. So, if you see your cat engaging in this behavior, don’t worry about it.

What Makes Cats Use a Flehmen Response?

Cats do not use a flehmen response every time they sniff something. Since the flehmen response is voluntary, they only use it when they smell something particularly interesting.

Some of the reasons why cats open their mouth when they smell something include:

• To investigate a strange or new odor
• To detect strange chemics
• To sense pheromones in feces or urine
• To determine a sexual partner’s readiness

These are some of the reasons that cats may use a flehmen response.

Do Other Animals Have a Flehmen Response?

Yes, many other different animals can use a flehmen response. This response is fairly common in different mammals. Some of the animals that look silly when pausing to sniff the air include:

• Giraffes
• Lions
• Hippos
• Giant pandas
• Tigers

These animals and many more engage in the flehmen response. They use this response in the same ways as cats for the most part.

So, now we have uncovered why cats open their mouth when they smell. The animals are learning more about their environment by using a specialized organ in their bodies to parse odors and pheromones. While cats look silly while using a flehmen response, it helps them contextualize the world around them.  

The photo featured at the top of this post is © iStock.com/Kseniia Soloveva