Cats smack their lips for reasons ranging from completely harmless to medically urgent. The most common triggers are nausea, something stuck in the mouth, or a scent-processing behavior that’s totally normal. Persistent or repeated lip smacking, especially when paired with drooling, appetite changes, or unusual behavior, points to something that needs attention.
The Flehmen Response: Normal Scent Processing
One of the most innocent causes of lip smacking is the flehmen response, sometimes called “stinky face.” Cats have a specialized scent organ called the Jacobson’s organ located in the roof of the mouth, just behind the upper front teeth. When a cat encounters an interesting smell, particularly pheromones from other cats, it will curl its lips, hold its mouth slightly open, and flick its tongue to push air up toward this organ. The result is a sensation best described as tasting and smelling at the same time.
This behavior looks odd. The cat may appear to grimace, sneer, or smack its lips repeatedly for a few seconds. It’s entirely voluntary and normal. You’ll typically see it after your cat sniffs another animal’s scent, a new object, or even your shoes. Wild cats and horses do the same thing. If the lip smacking only happens briefly after your cat investigates a smell, this is almost certainly what’s going on.
Nausea and Stomach Upset
Nausea is one of the most common medical reasons cats smack their lips. Before vomiting, a cat often goes through a recognizable pre-nausea phase: restlessness, anxiety, lip licking, excessive salivation, and repeated swallowing. Some cats cycle through this phase without ever actually vomiting, so you may only notice the lip smacking and drooling.
Occasional nausea from eating too fast or coughing up a hairball isn’t usually a concern. But frequent episodes can signal gastrointestinal inflammation, food intolerance, or a foreign object in the digestive tract. Cats with chronic kidney disease are especially prone to nausea. Vomiting occurs in 40 to 75 percent of cats with kidney disease, and the buildup of waste products in the blood can also cause painful mouth ulcers, creating a double source of lip smacking: nausea from the stomach and pain from the mouth.
Dental Pain and Oral Problems
Cats are remarkably good at hiding mouth pain, and lip smacking is sometimes the only visible clue. Tooth resorption, a condition where the tooth structure breaks down from the inside, affects a large percentage of adult cats. Once the damage reaches the surface of the tooth, bacteria invade and cause significant pain along with jaw spasms, increased salivation, oral bleeding, and difficulty eating. A cat dealing with this kind of discomfort may smack its lips, paw at its face, or chew on one side.
Other oral issues that trigger lip smacking include gum disease, ulcers from systemic illness, and a rare autoimmune condition called pemphigus vulgaris that causes blistering lesions inside the mouth. Cats with oral ulcers from any cause typically show hypersalivation, bad breath, and repeated lip smacking driven by pain. If your cat’s lip smacking comes with drooling, reluctance to eat hard food, or a foul smell from the mouth, an oral problem is high on the list.
Exposure to Toxins or Irritants
Cats that lick or chew on something toxic often react with immediate lip smacking, drooling, and frantic pawing at the mouth. Common household culprits include cleaning products, certain houseplants (lilies are particularly dangerous), essential oils, antifreeze, and topical flea treatments meant for dogs. Cornell University lists drooling, sluggishness, unsteady walking, heavy breathing, vomiting, and seizures among the typical signs of poisoning in cats.
Even non-toxic but bitter substances can trigger lip smacking. If your cat just licked something new, like a treated surface or a bitter-tasting medication, the smacking may simply be a reaction to the taste and should pass within minutes. If it doesn’t, or if drooling and lethargy follow, the substance may be genuinely harmful.
Stress and Anxiety
Lip licking and lip smacking can function as a displacement behavior, essentially a self-soothing gesture a cat uses when it feels uneasy. This is similar to how a person might bite their nails during a tense moment. Repetitive licking and grooming can calm a cat in the short term, but when the source of stress persists, the behavior sometimes becomes habitual.
Common stressors include a new pet or baby in the household, a recent move, changes in routine, conflict with another cat, or lack of environmental enrichment. If your cat’s lip smacking seems tied to specific situations and no medical cause is found, stress is worth investigating. Addressing the underlying tension, whether through environmental changes, more play, or separation from a bully cat, usually resolves the behavior.
Focal Seizures
This is the cause most owners don’t expect. A type of seizure called a complex partial seizure can look nothing like the full-body convulsions people associate with epilepsy. Instead, a cat may suddenly freeze, stare blankly into space (owners often describe it as “looking at the air”), and then begin lip smacking, chewing, facial twitching, licking, or swallowing. These episodes last a few seconds to about a minute.
A study of 17 cats with this seizure type found a strikingly consistent pattern: the episodes started suddenly, involved orofacial movements like lip smacking and chewing in every case, and often occurred in clusters over 24 hours. Behavioral changes and aggression between episodes were common. The seizures were frequently linked to a specific area of the brain involved in emotion and memory. In humans, the same type of seizure produces almost identical mouth movements and is associated with the same brain region.
If your cat has brief, repeated episodes of freezing and lip smacking, especially if it seems confused or aggressive afterward, this possibility is worth raising with your vet.
How to Tell What’s Causing It
Context is your best diagnostic tool. A single episode of lip smacking after sniffing the couch where a neighborhood cat sat is the flehmen response. Lip smacking followed by vomiting is nausea. Lip smacking that recurs throughout the day, especially alongside drooling, appetite changes, weight loss, or behavioral shifts, warrants a closer look.
Pay attention to the timeline. Sudden onset after your cat may have accessed a cleaning product or plant suggests toxin exposure. Gradual onset over weeks in an older cat, paired with increased thirst and weight loss, fits the profile of kidney disease. Episodes that come in clusters with staring and confusion point toward seizures.
Recording a video of the behavior can be extremely helpful if you end up at the vet. Many of these episodes are brief and hard to describe accurately. A short clip gives your vet far more information than a verbal account and can be the difference between a quick diagnosis and a lengthy workup.