Labiomental Groove: What It Is and Why It Looks Deep

The labiomental groove is the crease where your lower lip meets your chin. It is also called the mentolabial fold or mentolabial crease. On a side view, its common formula is MLA = ∠Li–Sbl–Pog′. This is an angle in degrees, not a raw distance or ratio.

Li marks the lower lip border, Sbl the deepest point of the crease, and Pog′ the most forward point of the soft-tissue chin. A smaller or larger angle isn't automatically better. It only describes one part of your profile in one image.

What makes the labiomental groove deep or shallow?

The groove is normal anatomy over a connected muscle system. Hur and colleagues examined 40 adult cadaver specimens in 2013. Upper mentalis fibers intermingled with the lower orbicularis oris in every specimen. The mentalis lifts the lower lip, so expression can change the fold during speech, smiling, lip pressing, or a posed photo.

Four visible factors can shape it: lower-lip position, chin projection, the dental relationship behind the lip, and expression. None works alone. A projected lower lip can sharpen the transition into the chin. A more forward soft-tissue chin changes the other side of the same angle. Lighting then controls how much shadow the groove casts.

Dental support can matter, but a selfie can't explain your bite. Arriola-Guillén and colleagues studied 138 radiographs from people aged 15 to 40 in 2025. Greater overjet and lower-incisor inclination were associated with smaller mentolabial angles. Their model explained 18.5% of angle variation, so most variation remained unexplained.

What a visible change may mean

What you notice	Possible explanation	Useful next check	What it cannot prove
The crease deepens when you press your lips	Muscle activity and lower-lip position	Compare a relaxed, closed-mouth profile	A structural chin or bite problem
The lower lip sits far forward in profile	Lip posture or dental support may contribute	Check whether the lips rest comfortably together	Tooth position from a photo
The crease changes after you tilt your head	Head posture changes the visible lip-chin transition	Retake the photo with a neutral head position	A change in facial anatomy
The line appears only under hard overhead light	Shadow is increasing local contrast	Compare soft light at face height	That the groove itself became deeper

How the labiomental angle is drawn on a side photo

Naini and colleagues described the standard three-point construction in 2017. You can reproduce it for education, but it isn't a clinical measurement.

1. Use a true side photo with relaxed lips. Keep the camera at face height, step back, and avoid a wide-angle close-up.
2. Mark Li at the midline border of the lower lip's red vermilion.
3. Mark Sbl at the deepest visible point between lower lip and chin. Mark Pog′ at the chin's most forward soft-tissue point.
4. Draw Li–Sbl and Sbl–Pog′. Measure the anterior angle where those lines meet.

The coordinate formula is θ = cos⁻¹[(Li−Sbl) · (Pog′−Sbl) / (|Li−Sbl| × |Pog′−Sbl|)]. Some papers use Sm or soft-tissue B for the deepest point. Others draw tangents rather than point-to-point segments. Fold-depth methods measure the perpendicular distance from Sbl to a line joining Li and Pog′. That is a raw distance, usually in millimetres. These conventions produce different numbers and aren't interchangeable.

Illustrative example

Take a synthetic 1,000-pixel profile, not a real person's photo. Suppose Li is (440, 260), Sbl is (395, 380), and Pog′ is (485, 530). The formula gives 128.5°. That number is only the geometry of this invented example.

Move Sbl three pixels right to (398, 380), while leaving the other points fixed. The result becomes 130.6°. A tiny landmark choice changed the angle by about 2.1°, although the pictured face didn't change.

Real photos add more uncertainty. Head tilt shifts the profile lines. A close lens changes relative projection, while lip tension moves Li and Sbl. In a 278-photo study, Leung and colleagues remeasured about 10% and reported a 2.76° method error. All participants were 12-year-old southern Chinese children. This isn't an adult reference range, but it shows why decimal precision can mislead.

There is no universal ideal angle

A photo angle is a description, not a beauty score. Naini's 2017 preference study used one digitally altered Caucasian male silhouette. Its 185 observers rated versions of that same image. The design cannot establish a perfect value across different faces, ages, ancestry, expressions, or camera setups.

The angle also doesn't reveal skeletal anatomy. It follows the visible skin outline, which includes lip posture and soft tissue. A side photo can't diagnose tooth position, jaw alignment, or treatment need.

That limit matters when you compare related proportions. The distance from nose to upper lip uses different landmarks from this fold. Our guide to upper-lip and chin proportions explains that distinction.

Safe ways to change how the fold reads

Styling changes contrast and framing. It doesn't remodel the groove.

Beard options

Even stubble across the chin and the area below the lower lip can soften the shadow boundary. A sharply shaved strip under the lip may make the crease more obvious. A fuller chin beard can draw attention to chin length instead. These are visual options, not rules. Use the approach that suits your hair density and upkeep.

If you want a broader framing decision, compare the examples in our beard styles by face shape guide. Hair, brow, and glasses choices affect the wider frame. They don't directly erase this local fold.

Lip-makeup options

A dark, crisp line along the lower lip creates a stronger edge above the groove. A softer, blended outline lowers that contrast. Centered gloss can pull light toward the lip, while a matte finish keeps reflections quieter. Try each under the light where you'll be seen or photographed.

Don't treat overlining as an anatomical correction. It changes the visible border, not Li, Sbl, or Pog′ beneath the makeup. For a controlled technique, follow the placement steps in our lower-lip makeup guide.

When a photo check is enough

If your concern is only how the fold looks in pictures, standardize the photo before judging it. Use the same camera, distance, head position, expression, and light. Then compare the crease itself, not a supposed ideal number.

If your bite feels uncomfortable, your lips don't meet comfortably, or your teeth concern you, ask a dentist or orthodontist. A profile photo can't diagnose a bite or jaw condition.

If beard framing is your next decision, the free face-shape finder estimates your visible outline on your device without an account or email. It doesn't reveal bone anatomy or prescribe a haircut or beard.