Understanding the Flehmen Response

Have you ever seen your horse curl its upper lip and appear to grin?

Despite appearances, your horse is not smiling. It is performing a natural behaviour known as the Flehmen Response, allowing it to analyse scents and chemical signals that the ordinary sense of smell cannot detect.

What Is the Flehmen Response?

The Flehmen Response is a normal behaviour seen in horses and many other mammals. By curling the upper lip, extending the neck and inhaling, the horse directs scent molecules towards a specialised sensory structure called the vomeronasal organ, also known as Jacobson's Organ.

What Is Jacobson's Organ?

The vomeronasal (Jacobson's) organ sits within the nasal region and is separate from the ordinary sense of smell. It is specialised for detecting pheromones and other chemical signals that provide information about other animals.

Why Do Horses Do It?

The Flehmen Response helps horses gather information about their surroundings and each other. They may perform it when:

· Investigating the urine or droppings of another horse.

· Meeting unfamiliar horses.

· Assessing whether a mare is in season.

· Exploring unusual smells in their environment.

Do Only Stallions Do It?

No. Although stallions display the Flehmen Response frequently when investigating mares, mares and geldings also perform it. The behaviour is simply part of how horses investigate important chemical information.

Why Does It Matter?

The Flehmen Response reminds us that horses experience the world very differently from humans. While we rely heavily on vision, horses also gather a remarkable amount of information through smell and chemical communication.

Recognising this normal behaviour helps owners avoid mistaking it for pain, aggression or unusual facial expressions.

Summary

· The Flehmen Response is a normal behaviour.

· It allows horses to analyse chemical signals and pheromones.

· It relies on the vomeronasal (Jacobson's) organ.

· Stallions, mares and geldings can all perform it.

· It is an important part of equine communication.

A Final Thought

The next time your horse curls its upper lip, remember that it isn't smiling—it is gathering information in a way humans never can. What looks like a funny facial expression is actually a sophisticated sensory system helping horses understand the world around them.

About the HØØF Knowledge Hub

The HØØF Knowledge Hub exists to provide horse owners with clear, practical and evidence-based information on hoof health, lower limb conditions and equine wellbeing.

Every horse is an individual, and no online article can replace professional assessment. If you have concerns about your horse's health or behaviour, always seek advice from your veterinary surgeon or registered farrier.

Article Information

Author: Paul Conroy BSc (Hons) AWCF
Organisation: HØØF Equine Hoof Care
Category: Equine Behaviour & Anatomy
Document Reference: HKH019
First Published: July 2026
Last Reviewed: July 2026