In short. How the balance between muscle groups produces a changed brow or smile, which changes settle, and what can and cannot be done about an expression you did not expect.
Key points
- An expression is the product of several muscles working together, so the assessment records the face at rest and through a series of movements rather than judging it in a photograph.
- That pattern is what allows the next plan to be aimed at the group that is under-acting, instead of adding treatment to the group that is already doing too much.
Patients often arrive expecting botulinum toxin to relax a line, and are surprised to find that what changed is an expression. A brow that now sits higher or lower, a smile that no longer reaches as far on one side, or a look in photographs that is hard to name. An expression is produced by a balance between muscle groups pulling in different directions, and treatment changes that balance rather than switching a single muscle off.
The brow is a balance, not a muscle
The brow is held in position by muscles that lift it and muscles that pull it down. Reducing the activity of the muscles that pull it down allows the lifting muscles to act more freely, which is why a brow can rise after treatment of frown lines. The reverse happens when the lifting muscles are treated or when the balance shifts the other way. The result can be a brow that sits higher, a brow that sits lower, or a brow whose shape has changed at its inner or outer end.
The smile has several contributors
A smile is not one muscle. The upper lip is lifted by muscles that run from around the mouth to the cheek and nose, and the corners of the mouth are pulled by others. Treatment around the mouth to soften lines can change the height of the smile, its symmetry, or the way the upper lip moves when speaking. Difficulty with certain sounds, or with drinking without spilling, belongs to the same group of changes and is assessed rather than ignored.
The pattern matters more than the muscle
An expression is the product of several muscles working together, so the assessment records the face at rest and through a series of movements rather than judging it in a photograph. That pattern is what allows the next plan to be aimed at the group that is under-acting, instead of adding treatment to the group that is already doing too much.
What can and cannot be done
Once the effect has settled, at about two weeks and usually by four, a changed brow or smile can be assessed and sometimes adjusted. What cannot be done is to undo the treatment: there is no dissolving agent, so the current effect runs its own course and the correction is planned around it rather than instead of it. Where the change is mild and appears only in certain expressions, leaving it alone is a legitimate answer, and it is one that a clinician should be willing to give.
Seek emergency care now if
- There is difficulty swallowing, speaking or breathing, or widespread muscle weakness.
- There is a rash, swelling of the lips or throat, or difficulty breathing soon after the injection.
- A weak smile or difficulty drinking without spilling is new and needs same-day care, and a drooping eyelid with double vision is an emergency.
Bringing photographs from before treatment to the assessment is more useful than describing the change, because the comparison separates a real shift in the balance from a difference that was always there.
Frequently asked questions
Why does my brow look different after treatment?
The brow is held by a balance between muscles that lift it and muscles that pull it down. Treatment changes that balance rather than switching one muscle off, so the brow can sit higher or lower than before, or change shape at its inner or outer end. Which way it moves depends on which muscles were treated and how strongly each was acting.
Why has my smile changed?
A smile is produced by several muscles pulling in different directions, so treatment around the mouth can change the height of the smile, its symmetry, or the way the upper lip moves. Some changes are the intended effect on lines around the mouth; others are a shift in the balance that produces the expression.
Can a changed expression be corrected?
Sometimes, once the effect has settled. A correction is planned at about two weeks at the earliest and usually at four, and it adjusts the muscle group that is under-acting rather than adding more to the one that is over-acting. Where the change is mild and visible only in expression, leaving it alone is a reasonable answer.
Risks & Limitations
- Botulinum toxin has no dissolving agent. An unwanted effect is managed by time rather than reversed, and nothing shortens it.
- The effect arrives gradually over several days and is judged at about two weeks, not on the day of treatment.
- Eyelid droop, brow change, facial asymmetry and a changed smile are recognised consequences of treating these areas.
- The rare findings that suggest spread beyond the treated area are difficulty swallowing, speaking or breathing, and widespread muscle weakness.
- Repeated treatment at short intervals is the main recognised driver of a reduced response over time.
When to Seek Care
- Difficulty swallowing, speaking or breathing, or widespread muscle weakness — seek emergency care now.
- A rash, swelling of the lips or throat, or difficulty breathing soon after an injection — seek emergency care now.
- An eyelid that has dropped and cannot be lifted, double vision, or an eye that cannot be closed — seek care the same day.
- A weak smile or difficulty drinking without spilling, and fever with spreading redness, heat or pus at an injection site — seek care the same day.
References & Further Reading
- U.S. Food and Drug Administration (FDA) — approved botulinum toxin products and their labelled warnings
- European Medicines Agency (EMA) — botulinum toxin assessment reports and product information
- National Medical Products Administration (NMPA, China) — approved products and their indications
- American Academy of Dermatology (AAD) — injectable safety information for patients
- 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.