What Is the Flehmen Response in Dogs?

We may think they’re quirky, but many of your dog’s eccentric behaviors actually have a biological backing, a real live reason why they may do something like, say, curl their lip upwards and expose their teeth.

This is what’s known as the flehmen response, and you may see your dog doing it when some smell is particularly interesting. Here’s why:

Overview of the flehmen response

It definitely makes for a good picture when a horse or goat raises their head in the air and curls their upper lip, showing their teeth. It can make us laugh, make us shake our head, or make us wonder what’s going on. Well, for horses and goats, along with a lot of other mammals including dogs, this is a natural biological response known as the flehmen response, which is named for the German word “to bare upper teeth.”

What does the flehmen response look like in dogs?

After having their nose buried in a clump of grass, fence post, or another dog’s rear end, you may notice them raise their head, open their mouth, and curl back their upper lip, exposing their top teeth.

They may rapidly chatter their teeth together, smack their lips or drool. This response typically lasts a few seconds but can be longer.

Science behind the flehmen response

In the animal world, scent and pheromones play a huge role in all forms of communication, especially when it comes to reproduction. Besides having an incredible sense of smell, dogs also have an additional olfactory organ called the vomeronasal, or Jacobson’s, organ located in their nasal cavity and opening into the roof of their mouth.

This specialized organ is directly connected to the brain and is able to detect pheromones, which are chemicals that are intended to affect the recipient’s responsive behavior. Pheromones are very important in male dogs determining a female’s reproductive receptiveness and for mother dogs to calm and bond with their puppies and for puppies to identify their mother.

Physiological mechanisms of the flehmen response in dogs

If pheromones and the vomeronasal organ make sense to you, then let’s talk about where the flehmen response comes in. The idea of raising their head, curling their upper lip, and opening their mouth helps to drive the pheromone particles into the vomeronasal opening that’s located in the roof of the mouth, just behind the front teeth. From there the particles are processed and information is sent directly to the brain.

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Purpose and function of the flehmen response in dogs

Dogs use scent as their main sense when it comes to interpreting their world, and a part of that sense of smell is their ability to detect pheromones using the vomeronasal organ. We’ve already established that pheromones play a role in reproduction and mothering, so it makes sense that the main function of the flehmen response is reproduction. Males will use this action to sort of drive a female dog’s pheromones into their vomeronasal organ to help them determine if she’s receptive to mating or if she needs a bit more time.

Reproduction isn’t the only reason a dog may use the flehmen response. They may also use it when investigating a urine marking or when trying to figure out another intense type of scent.

What it means when your dog has a flehmen response

If you notice your dog’s lip curling after some intense sniffing, it’s likely just them trying to work through what they just smelled. If your dog is intact, they may have detected a female in heat. If they are neutered, it’s likely them trying to identify and process another dog’s urine.

How does this response vary amongst different animals?

Dogs are actually pretty sly when it comes to performing the flehmen response. In fact, you may not even notice anything other than a raised head and a look of intense concentration on their face. If you really want to appreciate the flehmen response for all that it can be, check out a horse, cow, or goat. These animals really go through the motions, often holding the head-up-lip curled position for several seconds.

For dogs, their upper lip is more firmly attached and lacks the flexibility that a goat’s or horse’s does, so you may not see the same intensity of curling. But you still may get in on the teeth chattering and drooling.

What abnormal activities may look like the flehmen response?

If you notice your dog doing something weird with their lips or teeth, don’t just assume it’s the flehmen response, especially if they didn’t just get done smelling something. If you see teeth chattering, lip smacking, drooling, or strange lip movements it could be coming from a health condition. These could be signs of a seizure, neuromuscular issue, or dental disease, so have your dog checked out by a vet if you notice any abnormal behaviors.

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Why Does My Dog Keep Licking Their Lips?

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Bottom line

Our dogs often present with weird or interesting behaviors that most of us write off as quirky. One of those behaviors could be curling their upper lip and chattering their teeth. This may be the flehmen response, which is a dog’s way of further analyzing an especially interesting scent by driving the pheromone particles into the vomeronasal organ. This is a normal behavior for dogs, but if you notice anything abnormal about your dog’s behavior, don’t be afraid to contact your veterinarian.

 References

• “Canine Olfaction: Physiology, Behavior, and Possibilities for Practical Applications.” Animals. 21 Aug 2021. https://pmc.ncbi.nlm.nih.gov/articles/PMC8388720/.

•  “Pheromone.” Biology Online. 1 Mar 2021. https://www.biologyonline.com/dictionary/pheromone.