The orbicularis oris is the muscle that controls your lips. It closes your mouth, puckers your lips, and compresses them together. Every time you kiss someone, whistle, blow out a candle, drink through a straw, or pronounce the letter “B,” this muscle is doing the work. It’s also essential for keeping food and saliva inside your mouth while you chew.
How the Muscle Is Built
The orbicularis oris isn’t a simple ring of muscle fibers circling your mouth, though it’s often described that way. It actually has two distinct layers: a deep set of fibers and a superficial set, each with a different job.
The deep fibers run horizontally from one corner of your mouth to the other, staying close to the inner surface of your lips. These fibers act as a constrictor, pulling your lips together like a drawstring to create a seal. The lower border of these deep fibers curls outward, which is what gives the red part of your lips (the vermilion) its shape by everting the mucous membrane.
The superficial fibers connect to other muscles of facial expression and split into upper and lower bundles. These are responsible for the finer, more expressive movements: the subtle adjustments your lips make during speech, smiling, or showing emotion. So when you purse your lips in disapproval or pout, the superficial fibers are handling the nuance, while the deep fibers handle the seal.
Closing, Puckering, and Compressing
The orbicularis oris performs three core actions. When the entire muscle contracts evenly on both sides, it brings your lips together and closes your mouth. Isolated contractions of specific parts produce more targeted movements like pouting, pursing, twisting, or protruding the lips. And sustained contraction compresses the lips firmly against the teeth, which matters more than you’d think during everyday activities.
That compression is what creates a functional lip seal. Without it, you couldn’t build up air pressure in your mouth to whistle or blow, and you couldn’t create the suction needed to drink through a straw. Drinking by suction, in particular, depends on tightly pursed lips, making the orbicularis oris the primary muscle involved.
Its Role in Eating
During meals, the orbicularis oris works in partnership with the buccinator, a deeper muscle in your cheek. Together, they keep food where it needs to be while you chew. Electromyography studies show that the two muscles fire together in coordinated bursts, with the orbicularis oris contracting just before the jaw muscles clamp down.
Interestingly, the muscle is most active during food gathering, not chewing itself. Your lips, especially the lower lip, help collect and position food as you take bites and move pieces around your mouth. Once steady chewing begins, the orbicularis oris becomes less active and less rhythmic, letting the cheek muscles and tongue take over most of the positioning work. But the lip seal it maintains throughout the process is what keeps food and liquid from escaping.
Its Role in Speech
Clear speech depends heavily on precise lip movements. The superficial fibers of the orbicularis oris handle the rapid, fine adjustments your lips make when forming sounds. Bilabial consonants like “B,” “P,” and “M” require both lips to come together. Labiodental sounds like “F” and “V” need the lower lip to contact the upper teeth. Vowel shapes also depend on how rounded or spread your lips are.
These movements don’t happen in isolation. Research on speech coarticulation shows that your lips begin adjusting their position several consonants before a target vowel, meaning the orbicularis oris is constantly anticipating and preparing for upcoming sounds. This overlapping coordination is what makes fluent speech possible rather than a choppy sequence of individual sounds.
What Happens When It Stops Working
The orbicularis oris is controlled by two branches of the facial nerve (cranial nerve VII): the buccal branch for the upper lip and the marginal mandibular branch for the lower lip. When either branch is damaged, the results are immediately visible.
Bell’s palsy is the most common example. When the facial nerve becomes inflamed on one side, weakness or full paralysis can develop within hours to days. The affected corner of the mouth droops, making it difficult to smile, close the lips fully, or retain saliva. Drooling on the paralyzed side is a hallmark sign. People with Bell’s palsy also struggle with eating, drinking, and pronouncing bilabial sounds clearly, all because the orbicularis oris on that side can no longer do its job.
Facial nerve damage from trauma, surgery, or stroke produces similar effects. The degree of disability depends on how much of the nerve is affected and whether one or both branches are involved.
Why It Matters in Cleft Lip Repair
In babies born with a cleft lip, the orbicularis oris ring is interrupted. The muscle fibers on either side of the cleft are misaligned, with their direction and insertion points thrown off. This means the muscle can’t function as a continuous loop, so it can’t close or compress the lips normally.
Surgical repair focuses on restoring that continuity. Surgeons must independently reposition the three different components of the orbicularis oris: reinserting the nasal bundle into the correct anchor point, correcting the misdirected fibers, and joining the deep fibers end to end. When each component is repaired separately rather than stitched together as a single mass, the results are better both cosmetically and functionally, because each fiber group can resume its distinct role.
Measuring Lip Strength
Clinicians sometimes need to measure how strong the orbicularis oris is, particularly after a stroke or in patients with neuromuscular conditions. The standard tool is the Iowa Oral Performance Instrument (IOPI), which measures lip compression in kilopascals. In healthy adults aged 18 to 40, average lip compression strength is about 26.7 kPa.
For rehabilitation, therapists often set targets based on a percentage of that maximum. Stroke patients, for instance, may train at around 70% of their measured peak strength. Researchers have also validated a simpler method: testing how well someone can grasp a standard plastic water bottle with their lips alone, which correlates reasonably well with the IOPI and makes home assessment more practical.