Key Takeaways:
- Smile lines are the facial folds that run from the sides of the nose to the corners of the mouth. Clinically, they are known as nasolabial folds and are a normal anatomical feature present in every face.
- Smile lines are connected to other lower-face structures through the modiolus, but they are distinct from marionette lines and a down-turned smile despite often being grouped together.
- The visibility and severity of smile lines vary significantly between individuals. The NLF-SRS grading scale provides a standardised way to classify fold depth from minimal to extreme.
Smile lines are one of the most commonly recognised facial features associated with the area around the mouth. While the term is widely used, there is often confusion about what qualifies as a smile line, where it sits on the face, and how it differs from neighbouring facial folds.
Understanding the terminology and anatomy involved helps create a clearer distinction between smile lines and other lower-face concerns that are frequently grouped together.
The Facial Folds Commonly Referred to as Smile Lines
Smile lines are the folds that extend from the sides of the nose toward the corners of the mouth. In clinical settings they are referred to as nasolabial folds, and they exist in every face from birth.
Let’s be very clear here, they are a fold, not a wrinkle. This fold sits at the junction of the cheek above it and the mouth below. The modiolus, a dense point of muscle convergence at the corner of the mouth, anchors this junction and defines exactly where the fold sits on the face. The folds are highly visible during both facial expression and at rest.
Their appearance, depth, and visibility vary between individuals. On some they will appear as a shallow fold, and on others they may be much more prominent. While several facial concerns can appear close to this area, the term smile lines specifically refers to the folds that run between the nose and mouth.
What causes a deep or prominent fold is another matter entirely, and one the anatomy alone does not answer.
Marionette lines and down-turned smile are connected
Marionette lines and the downturned corners of the mouth are frequently grouped with smile lines without a clear understanding of how they connect. The connection is anatomical and it runs through the modiolus.
The modiolus sits at the corner of the mouth. It is a dense fibromuscular structure where multiple facial muscles converge, and it acts as the central anchor point for the lower face. The nasolabial fold, the oral commissure, the corner of the mouth where the upper and lower lips meet, and the marionette line zone all share this structure as a common reference point.
The depressor anguli oris or DAO is a triangular pair of muscles on either side of the chin and insert directly into the modiolus. Its function is to pull the corner of the mouth downward. When this muscle pulls the commissure down, the corner of the mouth follows. The line that extends below it is the marionette line.
Research published in the Journal of Cosmetic Dermatology on perioral anatomy confirms the modiolus as the structural point through which these lower face concerns connect. A downturned smile and marionette lines are connected to, but are not smile lines.
How smile lines vary across different faces
As children, most people have a visible transition between the cheek and the upper lip where the nasolabial fold sits. In younger faces the fold is often shallow and blends naturally into the surrounding facial contours. For most people this is how smile lines behave well into the twenties.
As people age, the fold may become easier to see at rest and more defined during facial expression. The degree of visibility varies significantly between individuals, with some retaining a relatively subtle fold throughout life while others develop a much more prominent appearance.
For some people the forties are where the fold becomes more consistently visible at rest. Two people the same age can show markedly different fold depth and definition depending on the face they started with.
Beyond fifty the fold is established at rest on most faces, sitting with greater definition than in earlier decades. Some people carry a shallow fold well into later life while others have had a defined resting crease since their thirties.
Smile lines alone do not indicate ageing. These folds are a normal anatomical feature found in every face. What changes over time is often their visibility, depth, and prominence rather than their existence.
How to self-identify smile line severity
While a consultation for smile lines is the only way to verify the severity of nasolabial folds, you can use the grading scale used by most clinics to get an understanding of where your smile lines sit. In practice, clinicians use the validated grading scales from the NLF-SRS (Nasolabial Folds Severity Rating Scale) that rates folds on a five point scale from none to extreme.
Grade 0: no visible or minimal fold
Grade 1: shallow but visible fold with a slight indentation
Grade 2: moderately deep fold
Grade 3: very deep fold, prominent facial feature
Grade 4: extremely deep and long fold with skin redundancy
To self assess, look at your face at rest in neutral, front-facing light. Avoid bathroom mirrors with harsh overhead lighting that exaggerates the depth of the crease. Because the scale is designed for a face at rest, the fold you observe when your facial muscles are completely relaxed is the one that reflects your baseline classification.
Most people fall between grade 1 and grade 3. Grade 4 is uncommon and typically involves visible skin redundancy beyond the fold itself. Regardless of your self assessment results, none of them are a medical issue and are not a reason to seek intervention. They are simply meant to help you understand where your smile lines st.
Professional standards at Luxe Lips
At Luxe Lips, a cosmetic clinic in Melbourne, our care is grounded in medical ethics and clinical responsibility. Every treatment pathway is approached as a medical process, with established health protocols and safety guiding each step.
Across our clinics in Moonee Ponds, Camberwell, and Brighton, our medical professionals carry out a thorough screening process for every person. For those exploring wrinkle treatment options for smile lines, this includes reviewing medical history, assessing skin quality, fold depth, and considering psychological readiness. In line with local guidelines, this evaluation helps determine whether a proposed plan aligns with your health.
Medical professionals proceed only when a treatment is clinically appropriate. If the underlying cause of smile lines, the condition of the surrounding skin, or your broader health profile means a particular approach isn’t the right fit, we will explain why and discuss what that means for you. The focus is always on clear information and maintaining a clinical environment where safety and ethical standards come first.
Because responses and circumstances vary, a consultation is required to determine suitability before wrinkle treatments are considered.
Note: Individual responses vary. A consultation with a qualified professional is required to determine the suitability of any treatment for your specific needs.
Questions we’re often asked about smile lines
Almost never exactly the same. Most faces show some difference between the left and right smile line, even on faces that read as symmetrical overall. One side might sit slightly deeper, run slightly longer, or curve at a slightly different angle than the other.
This is true across all grades on the scale. A shallow smile line can be more defined on one side than the other, and a more prominent fold can vary in depth from one cheek to the other. Both sides being identical is the exception rather than the rule.
What that difference looks like on your face is something a medical professional can examine in a consultation.
Absolutely, though it’s far less common than on older faces. Most young faces sit toward the lower end of the grading scale, but a smaller number sit higher from a young age, with a defined fold visible at rest in their twenties or even earlier.
When a young person has a deeper fold, it isn’t a sign of anything having gone wrong. The smile line is a fold that exists in every face from birth, and the depth a person carries it at is part of their facial baseline. A grade 2 or grade 3 fold on a young face is simply that face’s starting point.
Where your smile lines sit on the scale is something a medical professional can assess in a consultation.
Yes. The same fold can appear noticeably different in the morning compared to the evening, even though the underlying structure hasn’t changed. Faces tend to look slightly fuller and smoother first thing in the morning, with folds settling into greater visibility as the day goes on. By evening the same smile line can look more defined.
Lighting changes throughout the day also affect how the fold appears. Overhead light around midday casts more shadow into the fold than softer morning or evening light, so the same face can show different fold depth depending on when you look.
What you’re seeing at any given moment is something a medical professional can clarify in a consultation.
Cameras flatten the face in a way mirrors don’t. A smile line that catches modest shadow in person can appear much deeper in a photo because the lens compresses the three-dimensional structure of the face onto a flat plane, exaggerating any line or fold that sits at an angle to the camera.
Phone cameras in particular tend to overemphasise folds, partly from lens distortion at close range and partly from flat overhead lighting in most indoor settings. Selfie angles often make smile lines look more prominent than they appear in everyday life, and the resulting photo isn’t necessarily an accurate reflection of how the fold looks to other people.
What your smile lines actually look like in person is something a medical professional can identify in a consultation.
It can, and it’s one of the more common frustrations associated with smile lines. Foundation, powder and concealer tend to gather in the fold throughout the day, which can make the line appear darker, more textured, or more defined than the bare fold would on its own.
How much settling happens varies with product type and how dry or hydrated the surrounding skin is. Heavier formulas and powders sit in the fold more readily than lighter, more flexible products. The settling itself is a product behaviour rather than a change in the fold, but it can affect how the smile line presents through the day.
How your smile lines interact with the products you’re using is something a medical professional can walk through in a consultation.
