The muscle you use to suck in your cheeks is the buccinator. It’s a thin, flat muscle that forms the muscular wall of each cheek, sitting deep beneath the skin and several other facial muscles. When you contract it, it pulls your cheek inward against your teeth, creating that hollowed-out look.
Where the Buccinator Sits
The buccinator stretches from the back of your upper and lower jaw to the corner of your mouth. Its upper fibers attach near the back of the upper jawbone, its lower fibers start from a small ridge behind the lower molars, and its middle fibers originate from a bony hook near the back of the roof of your mouth. All of these fibers converge and insert at a small muscular knot called the modiolus, right at the corner of your lips.
This is a deeper muscle than most facial muscles. Sitting on top of it are several other muscles, including the masseter (the big jaw-clenching muscle you can feel when you bite down), the orbicularis oris (the circular muscle ringing your lips), and the risorius (the muscle that pulls your mouth sideways into a grin). Because the buccinator is woven underneath and between all of these, it plays a role in more facial movements than you might expect.
How It Creates the Sucking Motion
When the buccinator contracts, it compresses the cheek inward against the teeth and gums. But the mechanics are more interesting than simple flattening. Research on chewing function shows that when the buccinator fires, it actually thickens the entire cheek wall, behaving like a muscular hydrostat (think of how a tongue can change shape without any bones). This thickening and inward compression is what lets you create negative pressure inside your mouth, whether you’re sucking through a straw, whistling, or pulling your cheeks in for a selfie.
The buccinator doesn’t work entirely alone. At the corner of your mouth, its fibers blend directly into the orbicularis oris, the ring-shaped muscle around your lips. This connection matters because sealing your lips is part of creating suction. Together, the buccinator compresses the cheek while the orbicularis oris closes off the front of the mouth, letting you build the pressure difference that makes sucking possible.
Its Role Beyond Cheek Sucking
The buccinator’s main day-to-day job is actually chewing. Every time you eat, it keeps food positioned between your teeth so you can grind it properly. Without it, food would slip into the pocket between your teeth and cheek and just sit there. The muscle fires at the start of each chewing stroke, thickening the cheek wall to push the food back toward the tongue and onto the biting surfaces of the molars.
This same muscle is also essential for infants during breastfeeding. Babies have a structure called the buccal fat pad, a pocket of fat that sits between the buccinator on the inside and the jawbone on the outside. This fat pad counterbalances the negative pressure created during suckling, preventing the cheek from collapsing inward. It’s why babies have such round, full cheeks: the fat pad supports the buccinator while the infant nurses.
Because the buccinator interacts with so many overlapping facial muscles, it contributes to a range of expressions and actions. Blowing air (for whistling, playing a wind instrument, or blowing out candles), puffing your cheeks, and even grinning all involve the buccinator to some degree.
What Controls the Buccinator
The buccinator is controlled by the facial nerve, the seventh cranial nerve. This is the same nerve that controls all the muscles of facial expression, from raising your eyebrows to smiling. Despite being deeply involved in chewing, the buccinator is technically classified as a muscle of facial expression rather than a muscle of mastication. The true chewing muscles (like the masseter and temporalis) are controlled by a different nerve entirely, the trigeminal nerve.
This distinction has real consequences. In conditions like Bell’s palsy, where the facial nerve becomes inflamed or damaged, the buccinator can weaken or stop working. People with facial nerve paralysis often bite the inside of their cheek repeatedly because the buccinator is no longer holding the cheek wall taut against the teeth during chewing. They may also have trouble keeping liquids from leaking out of their mouth, since the cheek can’t maintain a proper seal.
Why Your Cheeks Look Different When Sucked In
The dramatic hollowed look you get from sucking in your cheeks comes from the buccinator pulling the soft tissue inward, away from the buccal fat pad. That fat pad is what gives your cheeks their normal rounded contour. When the muscle contracts forcefully, it compresses the space between the fat pad and the teeth, creating visible shadows below the cheekbones. People with less buccal fat naturally have more prominent cheekbone definition, which is why buccal fat removal surgery produces a similar look to the one you create temporarily by flexing this muscle.
The strength of the effect varies from person to person, depending on how much buccal fat you carry, the thickness of your buccinator, and how well you can isolate its contraction from the other muscles layered on top of it.