No one has established a definitive muscle count for smiling or frowning, and the popular claim that “it takes more muscles to frown than to smile” rests on shaky anatomical ground. The numbers you see repeated online (often 43 muscles to frown and 17 to smile, or 26 versus 62, depending on the source) have never been validated by a peer-reviewed study. The real picture is more interesting: facial muscles vary in number, shape, and attachment from person to person, different types of smiles and frowns recruit different muscle groups, and the way scientists actually study facial movement has moved well beyond simple muscle counting.
Where the Popular Numbers Come From
The “it takes more muscles to frown” factoid has floated around self-help books, motivational posters, and internet listicles for decades, but no one has been able to trace it to a published anatomical study. The numbers shift wildly depending on who’s telling the story. Some versions say 17 muscles to smile and 43 to frown. Others say 12 and 11, or 26 and 62. The variation alone is a clue that nobody is working from a shared scientific source.
The core problem is that “how many muscles does it take” is not a question anatomy can answer cleanly. A gentle closed-mouth smile uses fewer muscles than a full grin with crinkled eyes. A slight furrowing of the brow involves different muscles than a full theatrical scowl. And facial muscles themselves are notoriously hard to pin down: they’re thin, layered, and in many cases blend into one another without clear boundaries. Radiologists studying these muscles on imaging have noted that they are “often difficult to identify” even with advanced scanning technology.
The Key Muscles in a Smile
The star of every smile is the zygomaticus major, a paired muscle that runs from the cheekbone down to the corner of the mouth. When it contracts, it pulls your lip corners up and out. Research using automated facial image analysis has confirmed that visible zygomaticus major activity is the signature movement of smiling, driving the lip corners upward during both posed and spontaneous expressions.1PubMed Central. MOVEMENT DIFFERENCES BETWEEN DELIBERATE AND SPONTANEOUS FACIAL EXPRESSIONS: ZYGOMATICUS MAJOR ACTION IN SMILING Separate work has described the zygomaticus major as the muscle “predominant during smiling,” confirming its central role.2PubMed. Perception of activity in the Zygomaticus major and Corrugator supercilii muscle regions
But a smile rarely involves the zygomaticus major alone. In a full, genuine smile, the orbicularis oculi (the ring-shaped muscle around the eye) contracts too, producing crow’s-feet wrinkles and the “eye crinkle” that makes a smile look warm and authentic. Other muscles that can contribute include the levator labii superioris (which lifts the upper lip), the levator anguli oris (which helps raise the mouth corners from a deeper plane), and the risorius (which pulls the mouth corners sideways). Depending on how broadly someone smiles, even the buccinator in the cheek wall and the depressor septi nasi near the nose might get involved. A conservative count for a basic social smile might be four or five muscles on each side of the face. A broad, eye-crinkling grin could easily recruit ten or more.
The Key Muscles in a Frown
The corrugator supercilii, a small muscle near the inner eyebrow, is the classic “frowning muscle.” It draws the brows together and down, creating the vertical furrows between your eyes. Research has specifically identified it as the muscle “predominant during frowning.”2PubMed. Perception of activity in the Zygomaticus major and Corrugator supercilii muscle regions But “frown” is an ambiguous word. In everyday speech it can mean a brow furrow, a downturned mouth, a full-face scowl, or a look of sad displeasure. Each of these recruits a different set of muscles.
A brow frown relies heavily on the corrugator supercilii and sometimes the procerus (which pulls the skin between the eyebrows downward). A mouth frown, where the lip corners turn down, depends on the depressor anguli oris. A look of sadness can bring in the depressor labii inferioris, the mentalis (which crinkles the chin), and the platysma in the neck. Neurophysiological recordings from facial muscles have documented activity in the corrugator, depressor anguli oris, frontalis, and mentalis during expressions of sadness, confirming that the muscles of a “frown” depend entirely on what flavor of displeasure is being expressed.3PubMed Central. Organization of the central control of muscles of facial expression in man
This is why the muscle-counting game falls apart. If you define “frown” narrowly as a brow furrow, it takes as few as two or three muscles. If you define it as a full, dramatic expression of disgust or sadness involving the brow, mouth, chin, and neck, you can get well into double digits. The same sliding scale applies to smiling.
Why People’s Faces Are Built Differently
Even if researchers agreed on which muscles to count for a standard smile and a standard frown, the answer would still differ between individuals. Facial muscles show striking anatomical variation in size, shape, and attachment patterns. A well-studied example is the zygomaticus major itself. A meta-analysis across seven studies found that a substantial portion of the population has a “bifid” (split into two branches) zygomaticus major. The prevalence was highest in American study populations at about 34%, followed by Asian populations at roughly 27%, and European populations at around 12%.4PubMed. Prevalence of Bifid Zygomaticus Major Muscle A bifid zygomaticus major is the anatomical basis of cheek dimples: one branch inserts into the skin, creating the visible indentation when the muscle contracts. People with this variant are literally using a differently shaped muscle to smile.
Other facial muscles vary too. Some people lack a risorius muscle entirely. The depressor anguli oris can vary in width and overlap with neighboring muscles. The frontalis, which raises the eyebrows, sometimes extends farther down the forehead in some individuals than others. These variations mean that no single muscle count for smiling or frowning applies to everyone. Two people can produce what looks like the same expression using slightly different muscular machinery.
How Scientists Actually Study Facial Movement
Rather than counting muscles, researchers who study facial expressions use a system called the Facial Action Coding System, or FACS. Developed in the 1970s, FACS breaks down every visible facial movement into individual “action units,” each corresponding to the contraction of a specific muscle or muscle group. Raising the inner brow is one action unit. Pulling the lip corners up is another. A full smile or frown is described as a combination of action units, not as a raw muscle count. FACS has been described as “an objective method for quantifying facial movement in terms of component actions.”5PubMed Central. Classifying Facial Actions
This approach sidesteps the counting problem entirely. Instead of asking “how many muscles are working,” FACS asks “which visible movements are happening and how intense are they?” The system has become the standard tool in psychology, neuroscience, and computer science for studying expressions. It’s what underlies emotion-recognition software and the facial animation systems used in film and video games.
Not All Smiles Are Created Equal
FACS research has revealed that smiles differ from one another in important ways. The most studied distinction is between what’s sometimes called a “genuine” or Duchenne smile and a polite or social smile. A Duchenne smile combines action unit 12 (zygomaticus major pulling the lip corners up) with action unit 6 (orbicularis oculi contracting around the eyes). A polite smile involves just AU12 without the eye crinkle.
For decades, the Duchenne smile was treated as the reliable marker of genuine positive emotion. But recent research has complicated that picture. A study examining the relationship between AU6 (the eye crinkle) and AU12 (the lip pull) found that AU12 intensity was the dominant factor driving AU6 intensity. The relationship between actual amusement and AU6, once AU12 intensity was held constant, was negligible. The effect of AU12 intensity on AU6 was over twelve times larger than the effect of felt amusement.6PubMed Central. Reconsidering the Duchenne Smile: Indicator of Positive Emotion or Artifact of Smile Intensity? In other words, the eye crinkle may just be a side effect of smiling hard, not a reliable signal that someone is genuinely happy. People who produce bigger smiles tend to crinkle their eyes regardless of whether they’re actually amused.
This matters for the muscle-counting question because it means the muscular profile of a smile changes with its intensity. A low-intensity social smile might genuinely involve fewer muscles than a broad, intense one, but the difference is about how hard you’re smiling, not about whether you “mean it.”
Your Face Talks Back to Your Brain
One of the more surprising lines of research on facial muscles suggests that the act of smiling or frowning can influence how you actually feel. This is the facial feedback hypothesis, and while it’s been debated for over a century, experimental work has found real effects. In one set of experiments, participants rated stimuli as more pleasant when they were smiling compared to when they were frowning. The effect occurred during the facial action itself, with no lasting impact after five minutes or a day later.7PubMed Central. How the Experience of Emotion is Modulated by Facial Feedback The feedback was mainly attenuating: smiling during something negative made it feel less negative, rather than smiling during something positive making it feel more positive.
Other research has found that people who display Duchenne smiles report more positive experience when viewing pleasant scenes and humorous cartoons, and they tend to show different patterns of autonomic arousal when viewing positive material.8PubMed. Duchenne smile, emotional experience, and autonomic reactivity: a test of the facial feedback hypothesis Work on the sympathetic nervous system has shown that amplifying feedback from facial muscles during imitation of emotional expressions strengthens sympathetic activation, particularly in response to negative emotional cues.9Autonomic Neuroscience. An amplification of feedback from facial muscles strengthened sympathetic activations to emotional facial cues
The effects are real but modest. Forcing a smile won’t cure depression, and the effect evaporates quickly once you stop. Still, it suggests that the muscles of facial expression aren’t just output devices broadcasting your inner state to the world. They’re part of a feedback loop that shapes the emotional experience itself.
Botox and the Accidental Mood Experiment
Cosmetic botulinum toxin injections have provided an unexpected natural experiment in facial feedback. When injected into the glabellar region (the area between the eyebrows), Botox paralyzes the corrugator supercilii, the main frowning muscle. This smooths out “eleven lines” between the brows, which is the cosmetic goal. But research has found that the muscle relaxation can also disrupt the feedback loops that reinforce negative mood. Studies suggest that glabellar Botox injections can modulate amygdala activity, reduce symptoms of depression and anxiety, and strengthen emotional resilience.10PubMed Central. The Face of Emotion: Botulinum Toxin, Emotional Anatomy, and Mood Modulation
This is a growing area of clinical interest. If preventing a frown physically interrupts the loop between facial muscle contraction and negative emotional processing, it raises the possibility that targeted muscle interventions could have psychiatric applications beyond their cosmetic ones. The research is still preliminary, and the effect sizes are debated, but the basic observation is consistent with what the facial feedback literature predicts: change the muscle activity, and you can nudge the emotion.
The Left Side of Your Face Is More Expressive
Facial expressions aren’t perfectly symmetrical. Research on laterality has found that the left side of the face tends to be more emotionally expressive than the right, reflecting the right hemisphere’s dominance in emotional processing. A review of the literature concluded that the left side of the face is “more expressive of emotions, is more uninhibited, and displays culture-specific emotional norms,” while the right side “exhibits more universal emotional signals.”11PubMed Central. Laterality of facial expressions of emotion: Universal and culture-specific influences
This means the same smile can look subtly different on each side of your face, and the muscles on one side may contract more intensely than those on the other. It adds another layer of complexity to any attempt at counting: even within a single person’s face, the two sides don’t do the same work.
Where Smiling Came From
The evolutionary origins of the human smile shed light on why it involves the particular muscles it does. Among non-human primates, the expression most closely resembling a human smile is the “silent bared teeth” display. In most primate species, this display signals appeasement or submission and is typically directed by subordinate individuals toward dominant ones.12PubMed Central. Revisiting Darwin’s comparisons between human and non-human primate facial signals Over evolutionary time, as human social structures became more egalitarian and cooperative, the display appears to have shifted meaning from “I’m not a threat” to “I’m friendly” to the wide-ranging communicative tool smiling is today.
The silent bared teeth display in primates primarily involves retracting the lip corners and exposing the teeth, which is functionally what the zygomaticus major does in humans. The evolutionary story helps explain why this one muscle is so central to smiling: it’s the structure that produces the ancestral display. The eye crinkle, the nose scrunch, and the other flourishes of a human smile are later additions layered onto a much older muscular template.
When the Muscles Stop Working
Facial palsy, whether from Bell’s palsy, stroke, trauma, or surgical complications, highlights just how many muscles contribute to expressions we take for granted. When the facial nerve is damaged on one side, the muscles it controls go slack. A person with unilateral facial palsy may be unable to smile on the affected side, close the eye fully, or wrinkle the forehead. Reconstruction is a complex surgical challenge. If the nerve can be repaired within about six months of injury, direct repair is attempted. Beyond twelve months, when the muscles have atrophied from disuse, surgeons may need to transfer a functioning muscle from elsewhere in the body to restore movement. Donor nerves can come from the opposite facial nerve, the masseter nerve (which normally controls chewing), or the hypoglossal nerve (which normally controls tongue movement).13PubMed Central. Facial palsy reconstruction
Facial palsy reconstruction often focuses first on restoring the ability to smile, since smiling is so socially central. But the goal isn’t just to move the mouth corner upward. Surgeons work to recreate the coordinated action of multiple muscles so the result looks natural and spontaneous rather than mechanical. The difficulty of that task is itself evidence that a smile is not one muscle doing one thing. It’s an orchestrated event involving several muscles firing in a specific pattern, at specific intensities, with specific timing. Replicating that with transferred tissue and rerouted nerves is one of the most technically demanding areas of reconstructive surgery.