We use the acronym "LOL" dozens of times a day, often without so much as a twitch forming at the corners of our mouths. We offer polite, closed-lip smiles to strangers on the elevator. But when a friend tells a truly hilarious story, we might double over, breathless, tears streaming down our faces.
Clearly, not all expressions of amusement are created equal.
While both smiling and laughing fall under the umbrella of positive emotional responses, psychology and neurology show us that they serve different functions, originate from different parts of the brain, and signal vastly different things about our social state. Here is a deep dive into the psychology of a smile versus a genuine laugh.
The Anatomy of Amusement
To understand the psychological difference, we first have to look at the physical difference.
The Smile: A Voluntary Social Tool
Not all smiles are genuine. In 1862, French neurologist Guillaume Duchenne identified two distinct types of smiles:
- The Non-Duchenne Smile (The Social Smile): This smile involves only the zygomatic major muscle, which raises the corners of the mouth. It is voluntary, meaning we can fake it on command. We use it to be polite, to appease, or to mask other emotions.
- The Duchenne Smile (The Genuine Smile): This is considered the authentic smile of happiness. It involves both the zygomatic major (mouth) and the orbicularis oculi muscle, which causes the cheeks to lift and "crows feet" to form around the eyes. Crucially, the orbicularis oculi is largely involuntary. You can't easily fake a Duchenne smile if you aren't actually feeling positive emotion.
The Laugh: An Involuntary Eruption
While you can fake a chuckle, a genuine, belly laugh is an entirely involuntary reflex. It’s an autonomic response, much closer neurologically to sneezing or coughing than to speaking.
Laughter is messy. It disrupts our breathing, forces air out of the lungs in rhythmic bursts, and can even cause us to temporarily lose muscle tone (which is why you might feel weak in the knees when laughing hard). It’s an uncontrollable, full-body spasm that we surrender to.
The Neurological Crossroads
Smiling and laughing don't just look different; they are processed differently in the brain.
- Smiling (specifically conscious, social smiling) is heavily mediated by the conscious, higher-order areas of the brain, such as the motor cortex. We decide to smile at the cashier, and our brain sends the signal to the mouth muscles.
- Laughter is far older and more primal. It is linked to the brain's evolutionarily ancient subcortical regions, including the amygdala and the hypothalamus. These areas govern basal instincts, emotional responses, and autonomic functions.
When you experience a genuine laugh, you are temporarily bypassing the conscious control of the cerebral cortex. The evolutionary ancient parts of your brain have hijacked your body.
The Evolutionary Purpose: Why Do We Do It?
If they are so different, why do we have both? Evolutionary psychology provides a compelling framework for understanding their distinct roles.
Smiling: The "I am Harmless" Signal
Evolutionary biologists suggest that the human smile evolved from the "bared-teeth display" seen in other primates. While showing teeth can be a sign of aggression in many animals, the primate "silent bared-teeth face" is actually a sign of submission and non-hostility.
In humans, the social smile serves a similar function. It is a social lubricant. We smile to signal to others that we are friendly, that we are not a threat, and that we intend to cooperate. It’s a tool we use to navigate the complex social hierarchies of human interaction. We don't have to find something funny to smile; we just have to want the interaction to go smoothly.
Laughter: The Social Glue
Laughter, on the other hand, is a primal bonding mechanism. Anthropologist Robin Dunbar theorizes that laughter is essentially "social grooming."
Monkeys pick bugs out of each other's fur to bond; humans laugh. Laughter triggers a massive release of endorphins (the body's natural opiates), creating a shared sense of euphoria.
Crucially, laughter is highly contagious. We are 30 times more likely to laugh when we are with other people than when we are alone. When a group laughs together, they are engaging in a synchronized, involuntary display of vulnerability (remember, laughing impairs your ability to defend yourself or run away). This shared vulnerability and endorphin rush creates profound feelings of trust, safety, and group cohesion.
Summary: Control vs. Surrender
To summarize the psychology:
- A voluntary smile is an act of control. It is a tool we use consciously to manage social interactions, signal politeness, or appease others. It is the language of civilization.
- A genuine laugh is an act of surrender. It is an involuntary, primitive reflex that hijacks our bodies to create intense, immediate social bonds through shared euphoria and vulnerability. It is the language of the pack.
Next time you interact with someone, pay attention. Are you just exchanging pleasant, controlled smiles? Or are you pushing into the messy, involuntary, and profoundly connective territory of a genuine laugh? One smooths the path; the other builds the road.