This Bengal cat detects pheromones using its highly sensitive Jacobson's organ. (Image credit: Azovsky via Shutterstock)
When a cat is investigating smells, it will sometimes take on a funny expression on its face, as if surprised by an unpleasant aroma.
So why do cats actually make this unusual “stinky face?” It's not actually due to unpleasant odors, but rather because they are studying chemical cues in their environment.
Many animals, both wild and domestic, emit pheromones—chemical signals used to communicate within their own species. To detect and interpret these invisible messages, our furry friends rely on a special sensory organ located in the roof of their mouths, known as the vomeronasal organ, or “Jacobson’s organ.”
The organ is separate from the olfactory system (aka the nose), which detects scents but not pheromones, Alex Taylor, a feline welfare and behavior consultant at International Cat Care, explained in an email to Live Science.
When a cat encounters pheromones, it processes them differently than it processes scents. The cat instinctively opens its mouth and pulls its lips back, exhibiting a behavior known as the “Flehmen response.” This expression helps the pheromone molecules reach the vomeronasal organ, which enhances the cat’s ability to detect important chemical signals.
“While it may appear that a cat is grimacing, there is no emotional component to this behavior – the cat is simply detecting and processing pheromones,” Taylor said.
Cats use pheromones to communicate a variety of messages: They can mark their territory to avoid conflict or to strengthen the bond between mothers and their kittens, Taylor explained. Pheromones also communicate sexual status, indicating when a cat is in heat, added Mikel Delgado, a senior research scientist at the Purdue University College of Veterinary Medicine in Indiana.
According to Taylor, pheromones are secreted by specialized glands located in different parts of the cat's body, including the chin, cheeks, the space between the eyes and ears, the edges of the lips, the base of the tail, as well as around the genitals and anus, between the paws and nipples.
When cats rub their faces against objects, scratch surfaces, mark their urine, or defecate, they leave chemical messages for other cats, Delgado told Live Science in an email. Other cats then use their vomeronasal organ to analyze these scent marks and gather information about their neighbors.
During the Flehmen reaction, pheromone molecules enter the cat's mouth — either through licking or inhalation — and dissolve in saliva. They then travel through two passages in the roof of the mouth known as the nasopalatine ducts, which lead to a pair of fluid-filled sacs that make up the vomeronasal organ, Taylor explained.
When pheromone molecules reach the vomeronasal organ, they trigger neural signals that are sent to specific areas of the brain, particularly the amygdala, the hypothalamus, and the area responsible for sexual, feeding, and social behavior, Taylor added. Thus, chemical signals picked up by the vomeronasal organ directly influence a cat's behavior.
Unlike scents, whose meanings can change with new experiences, pheromones trigger instinctive responses. Cats don’t have to “learn” to recognize pheromones — the knowledge is built into their biology, Taylor said. Although pheromone responses are automatic, they can still be influenced by factors such as a cat’s development, environment, previous experiences, and internal states such as hormone levels, according to a review published in the Journal of Comparative Physiology A.
The vomeronasal organ is not unique to cats. A number of animals, from rodents to reptiles, also use this second sense of smell to detect pheromones.
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