Smile Lines: Causes, Assessment & Treatment Options
A smile line is not one thing. The muscles around the mouth fold the skin there every time you smile, laugh or speak, and that movement alone can mark the skin over years. Fat lost from the cheek removes the padding that used to keep the fold flat. And the cheek pad itself slides downward with time, which is what turns a line that appeared only when you smiled into a groove that is still visible when your face is completely at rest. Most faces carry all three in some proportion, and the proportion is what decides which option is worth considering. The distinction matters because the three parts answer to different things: movement answers to relaxing the muscle, volume answers to restoring it, descent answers to lifting, and a crease treated before the cause above it is identified usually looks better for a few months and then returns. There is a second reason this area is treated with more caution than the upper face. The muscles here are the ones a smile uses, so anything that reduces their pull can change a smile rather than only a line, and that trade is judged before treatment rather than discovered after it. This site is about why the fold is there, whether it needs anything doing, and what each path reaches and leaves alone.
Patient education reviewed by Tongchun Mao, MD. A fold that has appeared on one side only, that has come on over weeks, or that is accompanied by weakness, numbness or a mouth that no longer closes properly should be assessed medically before anything cosmetic is considered.
Six things that produce one fold beside the mouth
The first three carry most of the weight, and the last three decide how visible the result is. Which of them is doing the work in your own face cannot be read off a photograph, and it is the question an assessment exists to answer.
Movement: the muscles around the mouth fold the skin every day
The ring of muscle that closes the mouth and the muscles that pull the corner up and outward all gather the skin beside the mouth when they work. Smiling, laughing, speaking, eating and even holding an expression fold that skin in the same place thousands of times a day. On a face that has not yet lost volume or descended, this movement is the whole of the line, which is why it disappears completely when the face is at rest. It is also the part that no filler reaches, because the folding does not stop.
Volume: fat lost from the cheek leaves the fold unsupported
The cheek carries a pad of fat that sits over the fold and keeps the skin above it level with the skin below. As that pad thins with age, the crease no longer has anything holding it flat, and a line that was a shallow dimple on movement becomes a visible step in the surface of the face. This is the component that responds to restoring volume rather than to relaxing muscle, and it behaves differently depending on whether the cheek has merely thinned or has also begun to move downward.
Descent: the cheek pad slides down and the crease stays at rest
Separately from thinning, the soft tissue of the cheek migrates downward over years. The fold deepens from above as the tissue that used to sit over it settles below it, and at that point the line is present with the face completely still. Descent is the part that a filler placed into the fold cannot correct, because the tissue above the crease is what has moved, and adding volume below it changes the shape of the face rather than the line.
Skin: sun damage and thinning make the line read more strongly
Skin that has had a great deal of sun loses the collagen and elastin that let it spring back after being folded. The same expression leaves a deeper and more enduring mark in that skin than in skin that has been protected, and the fold casts a stronger shadow because the surface around it has changed. This is the component that surface treatments reach, and it is why two people with the same muscles and the same cheeks can reach their fifties with very different lines.
Bone and bite: the shape beneath sets the limit
The upper jaw and the cheekbone set how much the soft tissue is projected forward in the first place, and a face whose mid-face is flatter begins with less support over the fold. The bite matters for the same reason: a bite that has changed, teeth that have been lost, and a jaw that has been rebuilt all alter how the muscles around the mouth work and where the skin is gathered. This is the one item on the list that is worth investigating for its own sake rather than for the line.
Weight change: a thinner face shows what padding concealed
Weight lost deliberately or through illness removes fat from the face as well as the body, and the cheek is often where it shows first. A face that carried enough padding to keep the fold flat can develop a visible line within a year of losing weight, without any change in the muscles underneath. This is worth knowing because the line may be stable from that point rather than progressive, and because regained weight may change it again.
When a fold beside the mouth is not a cosmetic question
Almost every smile line is an appearance concern, the assessment is unhurried, and the answer is often that nothing needs doing. A small number are the visible part of something else, and what separates them is how the change arrived rather than how deep it looks. The finding that matters most is a fold that has developed on one side only in a face that was symmetrical, or that has come on over weeks rather than years, because the ordinary causes act on both sides over decades. Weakness on one side of the mouth, a corner that no longer lifts when you smile, numbness in the cheek, lip or chin, drooling, or a mouth that no longer closes properly all point away from the skin and towards the nerve that supplies it, and they need a doctor rather than an aesthetic consultation. A lump in the fold that is hard, fixed or growing, a sore that has not healed, bleeding or crusting from the line, or a spot that has changed colour or size is a dermatological matter and should be seen for its own sake. A fold that has appeared suddenly, or alongside weight loss, fever, a rash or a change in the general health of the skin, also belongs with a physician first. Where the line has been present for years and both sides are broadly equal, none of this applies, and the ordinary conversation about movement, volume and descent can begin on a sound footing. That conversation is what the rest of this site is about.
Five observations that decide the plan
A photograph taken in one light shows a line. It does not show how much of that line is movement, how much is lost volume, how much is descent, or what a smile would look like if the muscles producing it were quieter. Those are the questions the assessment exists to answer, and none of them can be answered from a picture.
The face in repose, with light across the cheek
The first observation is made with the face completely relaxed and the light directed across the cheek from the side rather than from above. Light from above deepens every fold artificially and light from the front erases them; light from the side shows the actual step in the surface. Whatever remains visible then is the part that lives in the tissue rather than in the movement, and it sets the ceiling for every option that works on muscle alone.
The same face mid-smile, held
The patient is asked to smile fully and hold it while the fold is examined. A line that appears or deepens sharply under load and disappears at rest is produced mostly by muscle pull and answers to the rung that reduces it. A line that is equally deep in both states carries a large component that will not respond to that rung at all. The comparison between the two states is the single most useful finding the assessment produces.
Where the cheek sits, and how much of it has moved down
The position of the cheek pad is recorded at rest, along with whether the tissue over the fold is level with the tissue below it or has slipped past it. A cheek that has thinned but not moved is a different problem from a cheek that has descended, and the two point to different options. This is also the observation that decides whether adding volume to the fold itself would help or would simply make the face look heavier.
The mouth corner at rest, and where the line begins
The resting position of the mouth corner, the height of the corner when smiling, and the point at which the fold starts are recorded before anything is discussed. These are the measurements that make a change in the smile a decision rather than a surprise, because a corner that already sits low, or one that lifts strongly and asymmetrically, has less room to change without the change becoming the complaint.
What the skin has kept, and the history behind it
The history covers sun exposure, smoking, weight change and its timing, dental treatment and bite, previous injections and when they were last given, previous filler in the cheek or the fold, and the family pattern. Taken together with the skin’s own quality and the pattern of the fold at rest, this decides what is worth doing, in what order, and what is not worth doing at all.
The ladder, from sun protection to the ceiling
The rungs run from measures that cost nothing to operations, and the useful part of the ladder is not the order but the matching. Each rung answers one of the three causes, and a rung used against a cause it cannot reach is either wasted or disappointing. At the bottom, daily sun protection and a short routine suited to skin that is folded many times a day change the skin’s capacity to spring back; they are the base every other rung sits on, and on their own their ceiling is low. Above that sit the measures that remove part of the drive to the muscles: a bite that is comfortable, teeth that are maintained, and a habit of expression that is noticed rather than changed. Then comes the rung that reaches the movement, reducing the pull of the muscles beside the mouth; it softens the fold while they are quiet, it wears off over months, and it can also change the smile, which is why it is used cautiously here and planned around the position of the mouth corner rather than around the line. Restoring volume comes next and belongs in the cheek rather than in the crease: it works best in a face that has thinned but not yet descended, because a cheek that has already moved down is not corrected by adding volume below the fold. Collagen biostimulators belong to the same step in the sense that they work on the thickness and quality of the skin, not on the depth of the fold, and the energy devices and threads reach laxity rather than a line that movement keeps recreating. Doing nothing is a legitimate choice at every rung, and for a stable fold in a face that still moves normally on both sides it is often the honest answer. The ceiling does not move: a lift changes descent, and nothing removes a fold that movement makes.
Four ways people make this worse
The first is to treat the crease itself while the cause above it is still working. Filling a fold that is being refolded every day, or that is deepening because the cheek above it has descended, buys a few months of a flatter line and then the same problem returns, and the volume added has changed the shape of the face in the meantime. The second is to accept treatment near the mouth without anyone looking at the mouth corner at rest and at the height it reaches on smiling, because the muscles that fold the skin are the muscles a smile uses, and a change in the smile is the specific trade of this area rather than a rare complication of it. The third is to spend years and a good deal of money on creams, rollers, patches and home devices for a fold whose main cause is the pull of a muscle or the descent of a cheek, because a topical changes the surface of the skin and cannot stop a fold from being made or a cheek from moving downward; the delay is the only part of that list that costs anything real. The fourth is to treat a fold that has appeared on one side only, has come on over weeks, or has arrived with weakness, numbness, drooling or a mouth that no longer closes properly as an appearance problem, when each of those needs a doctor and some of them are urgent. None of these are rare. Each is easier to avoid at the start than to repair afterwards, and each begins with a treatment chosen before the question was asked.
If the decision moves toward treatment
This site deliberately stops short of describing procedures, because the treatments themselves are explained properly elsewhere in this cluster. The category that restores volume in the cheek is set out on the dermal filler pages, and the rung that reduces muscle pull beside the mouth is described where the relaxing injections are covered in full. The suspension option and its limits are explained on the thread lift pages, and where the cheek rather than the fold is the main finding, that belongs with mid-face volume restoration. The surgical answer to descent is described on the facelift pages, and the wider assessment of the face as a whole sits within facial aesthetic surgery. Before any of them, quality and surgical safety describes how safety is organised inside the hospital, and booking an appointment explains how to arrange an assessment.
Smile lines: movement, volume and descent in one fold
Possible causes on the left and the ladder on the right, from least to most invasive. Note that only the middle rungs work on the fold itself, that the rung which reaches the movement is also the rung that can change a smile, and that the last line is the ceiling no rung reaches.
Guides
Ten guides, ordered the way the question usually unfolds: what people actually mean by the phrase, why one fold has three causes, how the fold is assessed in repose and mid-smile, and what each rung of the ladder reaches and leaves alone.
What Patients Mean by Smile Lines
Two complaints hide behind the phrase smile lines: the fold that appears only on smiling, and the groove that stays when the face is still.
Read the guide →Three Causes in One Fold: Movement, Volume and Descent
A smile line is movement, lost volume and descent mixed in one fold. Why the mixture, and not the depth of the crease, decides which option is worth considering.
Read the guide →The Line Only You See When You Smile
The fold that vanishes when you stop smiling is real, and it is harder to remove than most people expect. Why it differs from an established groove.
Read the guide →How Smile Lines Are Assessed
Light across the cheek, the face in repose, then mid-smile and held, the cheek pad and the mouth corner: the observations that decide the plan.
Read the guide →Why Filling the Fold Itself Often Disappoints
Filling the crease is the most intuitive treatment for a smile line and the most disappointing. What happens to material placed into a moving fold.
Read the guide →Injectables Near the Mouth and the Risk to Your Smile
The muscles beside the mouth are the muscles a smile uses. What reducing their pull can change about the corner and the two sides, and who should not be offered it.
Read the guide →Start with whether the line is there at rest
Arrange an assessment. We look at the fold in repose and on smiling, work out how much of it is movement, how much is cheek volume and how much is descent, and say plainly which options would change it and which would not.
Frequently asked questions
How can I tell which of the three causes is producing my own smile line?
By comparing the face in two states. A fold that is there only when you smile, and that disappears completely when you relax, is movement. A fold that is visible at rest but that flattens when the cheek is lifted gently with a finger is largely lost volume. A fold that stays and deepens when the cheek is lifted is descent. Most faces are a mixture of all three, and the proportions are what an assessment measures.
Is there any treatment that removes a smile line rather than softening it?
No. The rung that quiets the muscles stops the skin being folded while it is working, and the fold flattens during that time, but the muscle keeps working and the effect wears off. Volume restoration changes how flat the fold sits without removing it. A lift changes descent. Nothing removes a line that movement makes, and any description of a smile line as erased rather than softened is describing something that does not happen.
Why does a smile line look better straight after filler and then go back?
Because volume placed into a fold that is still being folded every day is gradually redistributed and the crease re-forms over it. The filler has not failed; it was asked to hold a line that the muscles beside the mouth recreate hundreds of times a day. When the fold is filling because the cheek above it has descended, the same applies and the added volume sits below the problem rather than over it.
What can change about my smile if the muscles beside my mouth are relaxed?
The muscles that gather the skin into a smile line are the muscles a smile uses, so reducing their pull can change how far the mouth corner lifts, how the upper lip moves, and how symmetrical the smile looks. Some of that is wanted and some of it is not, and which it will be is judged from the resting position of the corner and the height it reaches on smiling before anything is given, not from how it looks afterwards.
At what point does a smile line become a surgical question?
When the fold is present at rest and the tissue that used to sit over it has moved downward. That is descent, and it is the one cause that volume and muscle relaxation do not correct. Before that point a lift is usually more than the problem needs, and after it the non-surgical rungs tend to produce a flatter fold in a face that has not otherwise changed.
When is leaving a smile line alone the best answer?
When the fold is stable, when it is visible only on movement, and when both sides of the face still move normally. That is a working face rather than a condition, and no treatment improves it as much as the description suggests. It is also the honest answer for anyone whose expectations require the line to be gone, because the muscles that make it keep working whatever is done.
Part of Lines and Wrinkles — 9 sites on this topic