Types of Smiles and What They Mean: A Science-Backed Guide

The Facial Action Coding System (FACS), developed by Ekman and Friesen in the 1970s, classifies facial expressions by the specific muscle groups (Action Units) they activate. A smile is not a single Action Unit — it is a combination, and which muscles are included determines what type of smile it is and what it communicates.

The two most fundamental categories are Duchenne smiles (genuine, involving both the zygomatic major and the orbicularis oculi) and non-Duchenne smiles (voluntary, involving only the zygomatic major that raises the mouth corners). This distinction underlies almost all smile-type classifications — genuine smiles always involve the eyes; most performed or social smiles do not.

Recent research has expanded the taxonomy further. A 2017 study by Martin and colleagues identified that humans actually produce two distinct categories of genuine smile — reward smiles and affiliative smiles — each involving the zygomatic major but with different intensities and secondary muscle activations. The research on smile types is still active and continues to refine what was a simpler binary model.

The Duchenne smile is the gold standard of genuine smiles. Named after neurologist Guillaume-Benjamin Duchenne, who first documented it in 1862, it requires simultaneous activation of the zygomatic major (raises the mouth corners and upper lip) and the orbicularis oculi (raises the cheeks, narrows the lower eyelids, and produces crow's feet at the outer eye corners).

What makes the Duchenne smile uniquely reliable as a signal is that the orbicularis oculi cannot be activated voluntarily in most people. Studies show that fewer than 10% of people can consciously contract this muscle without genuine emotion. This means that when someone's eyes fully engage in a smile — the cheeks rise high, the lower eyelids narrow, the outer eye corners crinkle — the emotion behind it is almost certainly real.

The Duchenne smile produces the highest ratings for warmth, trustworthiness, and attractiveness of any smile type. It is also the expression that AI smile analyzers are specifically designed to detect and score — the eye engagement component (orbicularis oculi activation) is weighted heavily because it is the most reliable differentiator between genuine and performed smiles.

The Pan Am smile — named after the flight attendants who were trained to maintain a fixed, pleasant smile throughout a flight — is a deliberate, voluntary smile using only the zygomatic major. The mouth corners are raised, the lips may part, but the eyes remain largely uninvolved. No cheek lift. No eye narrowing. No crow's feet.

This is the smile people produce on command for photos, in professional contexts, and in social situations where they want to appear pleasant but are not genuinely amused or happy. It is not dishonest — it is a recognised social tool. Most people can produce it reliably, and most observers recognise it as a social rather than genuine smile, even if they cannot articulate exactly why.

The Pan Am smile tests poorly for warmth and trustworthiness compared to the Duchenne smile, but it performs better than no smile at all. In situations where a genuine smile is not available, a well-produced polite smile still signals social cooperation and positive intent.

The 2017 Martin et al. research identified three functionally distinct genuine smile types beyond the Duchenne/non-Duchenne binary. The reward smile signals happiness and positive experience — it is the biggest, most symmetric, most eye-engaged smile type. This is what your face does when you find something genuinely funny or when something unexpectedly good happens.

The affiliative smile is subtler — smaller mouth engagement, eyes slightly engaged but not maximally. It signals social connection and goodwill rather than peak happiness. This is the smile you give a stranger to indicate you mean no harm, or the smile you hold during a warm conversation. It does not require peak emotion to be genuine.

The dominance smile is asymmetric — typically stronger on the left side of the face (from the viewer's perspective, the smiler's right). It conveys amusement in a slightly condescending way — the smile of someone who finds a situation mildly ridiculous rather than genuinely funny. It is frequently misread in social contexts and can come across as dismissive if the receiver is not attuned to the asymmetry.

The contempt smirk is a unilateral smile — only one side of the mouth turns upward, while the other side either stays flat or turns slightly down. Ekman identified it as the only universal asymmetric facial expression and specifically associated it with feelings of contempt or moral superiority. It is culturally consistent: a unilateral mouth raise reads as contempt across cultures that had no contact with each other.

The miserable smile — described by Ekman as a 'felt, miserable smile' — is a Duchenne smile that occurs while experiencing genuine negative emotion. It appears when people try to maintain composure in difficult situations, such as receiving bad news in a social context. The eyes genuinely engage (orbicularis oculi fires), but the context and secondary expressions reveal distress beneath. It is one of the most poignant expressions in the human repertoire.

Both of these smile types are important to recognise because they are frequently misread. A contempt smirk is often interpreted as a charming half-smile; a miserable smile can be read as positive when the person is actually struggling. Reading these correctly requires attending to context and the full-face expression, not just the mouth region.

Knowing which smile type you most commonly produce changes your approach to improving it. If your default smile is a Pan Am (mouth only, eyes uninvolved), the development target is the orbicularis oculi — the eye muscle. Practice involves connecting to genuine emotion before expressing the smile, not just trying to 'include your eyes' as a mechanical instruction.

If your smile is asymmetric, the target is bilateral coordination. Practicing in a mirror while focusing on equal activation on both sides, combined with relaxing jaw tension on the tighter side, often produces visible improvement within weeks.

An AI smile score gives you a data-driven baseline for which components of your smile are strongest and which need development. The four signals measured — mouth curve, cheek lift, eye squint (Duchenne marker), and jaw openness — map directly to the muscle activations that distinguish the major smile types. Tracking these scores over time makes your practice targeted rather than vague.