In short. Asymmetry may sit in the muscle, in the vermilion or in the face around the mouth. It is measured at rest and on smiling before anything is treated.
Key points
- Muscle answers to relaxing and wears off.
- Vermilion answers to volume and can be dissolved.
- The face around the mouth answers to neither, and a lip treated for a difference that is not in the lip tends to look more uneven afterwards.
Almost every mouth is asymmetric. The question is not whether a difference exists but where it sits, because a difference in the lip, in the muscle and in the face around the mouth are three problems with three answers.
Measured before it is treated
The assessment compares the two sides at rest and while the mouth is moving, because a difference that appears only on smiling is a muscle finding and one present at rest is usually a tissue finding. The height of the vermilion and the position of the border are compared on each side, and the mouth is read against the nose and the chin rather than on its own. Photographs at rest and on movement are part of the record, because a difference stable over time is judged differently from one that is changing.
When the difference is in the muscle
One side of the smile rises higher, or one corner is pulled down more, and the lip itself is even when the face is still. This is a finding about movement, and the reversible route is to relax the muscle that is doing more work. It wears off, which matters because the balance has to be judged while the effect is present, and a plan that overshoots leaves the mouth uneven in the other direction until it fades.
When the difference is in the vermilion
One side of the lip carries more tissue than the other, at rest as well as in movement. This is the finding added material reaches, and because it can be dissolved, an adjustment can be made at a follow-up. The amount needed is usually small, and the aim is a mouth that reads as even rather than one that measures as identical, because perfect symmetry is not what most faces have.
When the difference is in the face around it
A nose that leans, a chin that sits off centre, a bite that meets unevenly or a jaw that is different on the two sides will all make an ordinary lip look uneven. In these cases the lip is not the finding, and treating it changes the lip without changing what is being seen. Where the difference is in the teeth or the bite, it belongs to a dental or jaw assessment. Where it is in the nose or the chin, the guides for those areas are where the decision belongs.
Three levels, three answers
Muscle answers to relaxing and wears off. Vermilion answers to volume and can be dissolved. The face around the mouth answers to neither, and a lip treated for a difference that is not in the lip tends to look more uneven afterwards.
A difference that needs assessment rather than treatment
- Weakness or drooping of one side of the face that is new or sudden.
- Numbness of the lip or chin that is new, spreading or not recovering.
- A difference that has appeared over months, or with a lump or a sore.
Frequently asked questions
Is it normal for the two sides of the mouth to differ?
It is close to universal. Faces are asymmetric in small ways throughout, and the mouth is one of the places where it is most often noticed because the lip has a clear edge and a colour boundary to compare. The useful question is not whether a difference exists but whether it is visible at conversational distance, whether it is stable, and whether it sits in the lip at all. A difference nobody else can see is often better left alone.
Which asymmetry can filler balance, and which can it not?
Material placed in the lip can balance a difference in the amount of tissue between one side and the other, which is a genuine tissue finding. It cannot balance a difference produced by muscle, because the muscle will still move the lip further on one side, and it cannot balance a difference created by a nose that leans or a chin that sits off centre, because the lip is not what is uneven. Treating a muscle or facial difference with volume generally makes it more visible rather than less.
Can treating one side make the difference more obvious?
It can, and this is the main risk of treating asymmetry without measuring it first. Adding material to the smaller side changes the lip, while the muscle or the underlying facial difference continues to do what it did, and the two effects can read as a new unevenness rather than a correction. This is why the assessment watches the mouth in movement as well as at rest, and why some differences are left alone rather than treated.
Risks & Limitations
- A dissolvable gel filler can be broken down with an enzyme. Skin or tissue removed by an operation cannot be put back.
- Bruising and swelling after a lip injection are common and usually settle over one to two weeks.
- Repeated filler over years can accumulate in the lip, and dissolving may not return it to its untreated state.
- Every operation on the lip leaves a scar, and the lines above the border and the way the mouth closes can change.
When to Seek Care
- Severe pain, blanching or mottled skin during or after a lip injection, or a change in vision.
- A sore, ulcer or white patch on the lip that has not healed in a few weeks.
- A lip that is numb, or a mouth that no longer closes, after an operation.
- Fever with spreading redness, warmth or discharge, or a wound that opens.
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.