Upper Lip Curl / Flehmen Response
Look at the signal, then look at the whole horse and the situation around it.
NOTICE
The horse lifts or curls the upper lip, often with the head slightly raised. This is called the flehmen response.
You may notice:
- the upper lip rolling upward
- the nostrils changing shape
- the head lifting
- a pause while the horse investigates a scent
- sniffing just before the lip curl
WHAT IT MAY TELL YOU
Flehmen helps horses gather more information about certain scents and chemical signals.
You may see it after a horse smells another horse, urine, manure, a new object or substance, or something unusual in the surroundings.
The horse is investigating information, not simply “making a face.”
DON'T ASSUME
A curled upper lip doesn’t automatically mean the horse is smiling, disgusted, thinks something smells bad, or is being silly.
Instead, ask: “What did the horse investigate just before the lip curled?”
LOOK AGAIN
Watch the sequence.
Did the horse sniff something first? What was the nose directed toward? Did the head rise? Is another horse nearby? Is the horse investigating urine, manure, or a new scent? Does the horse return to normal behavior afterward?
SAFETY
Flehmen is usually part of scent investigation, but repeated lip curling without an obvious scent to investigate can sometimes appear alongside physical discomfort.
Pay closer attention if it appears with pawing, looking toward the belly or flanks, reduced interest in food, sweating without an obvious reason, repeated lying down or rolling, restlessness, or other unusual behavior.
If those signs are present or the horse seems uncomfortable, look beyond normal flehmen and consider whether veterinary attention may be needed.
Research / Learn More
What research shows
The flehmen response helps horses investigate poorly volatile chemical information through the vomeronasal system. It is normal in scent and social investigation. Equine discomfort research also notes that flehmen can occur outside its usual olfactory context when a horse is uncomfortable.
What it does not tell us
A lip curl by itself does not identify an emotion, and flehmen can occur in healthy horses as well as in some pain contexts.
Sources
- Sensory Abilities of Horses and Their Importance for Equitation Science — explains the vomeronasal organ and how flehmen supports analysis of certain chemical compounds.
- Equine Discomfort Ethogram — describes normal olfactory flehmen and notes that spontaneous flehmen may also appear with discomfort outside that context.
- Facial expression-based acute pain scale in foals — shows why flehmen should not be treated as a pain sign by itself: healthy foals also displayed it.