Asymmetric smile after botulinum toxin
Quick facts
- Definition
- A difference between the two sides of the smile that appears or worsens after a botulinum toxin injection.
- Most common cause
- The toxin's effect on a smile muscle next to the target, or a difference in response between the sides.
- Muscles involved
- Zygomaticus muscles, lip elevators, risorius, orbicularis oris, lower lip depressors.
- Duration
- Temporary; tends to improve as the toxin effect wears off, over weeks to a few months.
- Relevance in HOF
- Aesthetic and functional complication of the midface and lower face; prevention starts at the assessment.
An asymmetric smile after botulinum toxin is a difference between the two sides of the smile that appears or worsens after an injection. One mouth corner rises less, the lip stays stiller on one side, or the smile looks "pulled". In most cases, the botulinum toxin acted on a smile muscle next to the target muscle, or the two sides responded differently. It is temporary, but it bothers patients a lot, because it shows in every conversation and every photo.
Which muscles are usually involved?
The smile depends on several muscles working together. The table links the treated area to the muscle that may be affected:
| Treated area | Muscle that may be affected | How it shows |
|---|---|---|
| Crow's feet (lower part) | Zygomaticus major and minor | Mouth corner rises less on one side |
| Nose lines and gummy smile | Levator labii superioris alaeque nasi | Upper lip drops, smile shows fewer teeth on one side |
| Masseter | Risorius and zygomaticus major | Stiff smile or shorter smile sideways |
| Mouth corner | Depressor anguli oris and depressor labii inferioris | Lower lip drops less on one side when speaking and smiling |
| Lips | Orbicularis oris | Weaker lip, difficulty whistling, drinking through a straw or articulating some words |
There are also causes that do not involve spread: differences in dose or response between the sides, a stronger muscle on one side, and a pre-existing facial asymmetry that became more noticeable.
When does it appear and how long does it last?
The asymmetry usually appears when the toxin starts to work, in the first few days, and becomes clearer within one to two weeks. It tends to improve as the toxin effect wears off, over weeks to a few months, depending on the muscle and the dose. A drooping lip caused by an effect on the upper lip is covered in lip ptosis after toxin.
How to reduce the chance and how to manage it
- Photograph the smile beforehand: social and full smile, front view, under the same conditions at the follow-up visit. A documented pre-existing asymmetry avoids arguments later.
- Observe the strength of each side: sides with muscles of different strength may call for different planning.
- Ask about previous injections: the past response helps predict behavior.
- At the follow-up visit: compare the photos, separate what is new from what was already there, and explain the recovery time.
An overview of complications is in complications with botulinum toxin, and the map of treated muscles is in muscle map for botulinum toxin.
Also called: crooked smile after toxin, post-toxin smile asymmetry, toxin-induced smile paresis.
Frequently asked questions
Does a crooked smile after botox go back to normal?
Usually yes. The toxin has a temporary effect, and the smile tends to rebalance as the muscle regains strength, over weeks to a few months. The professional assesses at the follow-up visit whether anything needs adjusting.
Why did my smile become asymmetric if the toxin was injected around the eyes?
Crow's feet sit close to the origin of the zygomaticus muscles, which lift the corner of the mouth. If the toxin acts on them on one side, that side rises less when smiling.