In short. 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.
Key points
- The resting position of the mouth corner and the height it reaches on smiling are recorded before treatment, and they are what any change is judged against.
- A patient who needs the smile to stay exactly as it is should hear plainly that this option is not for them.
The muscles beside the mouth are the ones a smile uses. That makes treating this area different from treating the upper face, where the muscles being quieted are largely ones of expression. Reducing their pull can soften a fold, and it can also change how a smile looks and how even it is.
What can change
The corner of the mouth may lift less far on the treated side, and the upper lip may move differently when speaking. The two sides may not match as closely as they did, and the difference is often more noticeable in a photograph than in a mirror. Some of these changes are what a patient wanted. Others are not, and which one occurs cannot be promised in advance.
Why asymmetry is the specific risk here
The two sides of a face are never identical, and they are not treated identically either. A muscle that is stronger on one side, or a resting corner that already sits lower on one side, changes what the same treatment does. A change that would be even in theory can be uneven in practice, and the assessment exists to predict that rather than to discover it afterwards.
The corner position is the measurement
The resting position of the mouth corner and the height it reaches on smiling are recorded before treatment, and they are what any change is judged against. A patient who needs the smile to stay exactly as it is should hear plainly that this option is not for them.
Who should not be offered it
Anyone whose work or sense of themselves depends on a smile that behaves in a particular way is a poor candidate, and that is a legitimate reason rather than an unreasonable one. So is a patient who has had an uneven result here before, and one who expects the line to be gone.
What this option cannot do
It cannot remove a groove already present at rest, because that component sits in the tissue rather than the muscle. It cannot correct descent, because the tissue above the fold has moved and relaxing a muscle does not put it back. And it does not last, because the muscle recovers and begins folding the skin again.
If it changes and you do not want the change
Most of what changes is temporary, because the effect on the muscle fades over months. That is the reassurance in this area, and it is also why caution matters: the question can be revisited later, but what happened on the day cannot be undone on the day.
Three things to raise before treatment
- Any occasion in the next few months when your smile will be on show.
- Whether the two sides of your smile have ever been uneven.
- What you expect the line to look like afterwards.
Where the volume component fits instead is described in volume restoration before descent sets in. The options that reach laxity rather than movement are covered in devices and threads in the mid-face.
Frequently asked questions
How can relaxing a muscle beside my mouth change my smile?
The corner of the mouth may lift less far on the treated side, the upper lip may move differently when speaking, and the two sides may match less closely than they did. Some patients want exactly that, because a slightly lower corner is the point. Others do not, and which of the two occurs cannot be promised in advance. It is judged from the corner position you have before anything is given.
Which smile lines should not be treated with a relaxing injection at all?
A fold that is stable and visible only on movement, in a face where both sides already behave the same way, is the clearest case where the trade rarely favours treatment. So is a patient whose smile has to stay exactly as it is, one whose face is already uneven in a way treatment would make more obvious, and one who has had an uneven result in this area before.
Does the effect wear off, and does that make it a safe place to experiment?
The effect on the muscle wears off over months, which is the main reassurance in this area and is also why revisiting the decision is possible. It does not make the area casual, because what changes for those months is how your face looks when you speak, eat and smile, and you cannot undo it on the day. Cautious and reversible are not the same thing.
Risks & Limitations
- Reducing the muscle that pulls the fold also changes how the smile looks. That trade-off is the treatment, not a side effect of it.
- A fold that movement recreates is not removed by filling it. Material placed in a moving crease can look heavier over time rather than flatter.
- Mid-face filler can be dissolved, but the face rarely returns to exactly what it was before.
- No treatment removes a smile line. Lines soften, and they return as the face keeps moving.
When to Seek Care
- Severe pain, blanching or a mottled colour change in the cheek or around the mouth after an injection — seek care immediately.
- A smile that has become uneven, or a corner of the mouth that droops, after a procedure.
- A change confined to one side of the face, or numbness or tingling that does not settle.
- Difficulty breathing or chest pain — seek emergency care immediately.
References & Further Reading
- American Society of Plastic Surgeons (ASPS) — procedure and safety guidance
- National Institute for Health and Care Excellence (NICE, UK) — relevant guidance
- Cochrane Library — systematic reviews
- Chinese Medical Association Plastic Surgery Branch — clinical guidance
This page is patient education, not medical advice, and it does not cite individual studies. Discuss your own case with a qualified clinician. To arrange an assessment at Chongqing West District Hospital, see Contact & Consultation.