Smile changed after Botox: why, how long and what to do

Your smile is symmetrical, but it no longer quite looks like yours: it seems less wide, less spontaneous, a little frozen, or your upper lip no longer rises as it used to. After a botulinum toxin injection around the eyes, the mouth or the jaw, this change is possible. It is one of the smile problems after a botulinum toxin injection. It is temporary: the smile regains its usual look as the effect of the toxin wears off. This page answers the seven questions people ask most often.

Why does the smile change?

A natural smile results from the coordinated action of many small muscles: some pull the corner of the mouth upwards, others lift the upper lip, and others again crinkle the eyes or lower the lower lip. If the toxin relaxes one of them on both sides, the smile stays symmetrical but loses part of its movement.

Depending on the area injected, the sources describe several mechanisms:

• around the eyes: the label of a type A toxin recommends avoiding injections too close to the zygomaticus major muscle, which lifts the corner of the mouth, to prevent the lip from drooping¹;
• at the corner of the mouth: an expert consensus on the lower face lists, among the complications of treating the muscle that pulls down the corner of the mouth, a flattened lip and facial expressions judged unsatisfactory, as well as difficulty opening the mouth wide²;
• at the jaw: in a large series of 383 people treated in the masseters, eight reported an unnatural-looking smile³;
• for a gummy smile: relaxing the muscles that lift the upper lip changes, by definition, the way you smile; lip length must be assessed before treatment to avoid complications⁸.

These changes are explained by an effect of the product on the targeted muscle that is stronger than intended, or by spread to a neighbouring muscle². Bear in mind that, apart from frown lines, crow’s feet and the forehead depending on the product, the French product labels provide for no aesthetic indication: injections of the mouth and jaw are off-label⁵.

How soon after the injection does it appear?

It appears as the effect of the toxin builds up: side effects are usually seen in the first few days⁵, within the first week according to the US label of a type A toxin⁶. After an injection of the masseters, the effect of the toxin on this muscle builds up more slowly, over 2–4 weeks in a large series³: a change in the smile may therefore be noticed later.

How long does it last?

It lasts at most as long as the effect of the toxin on the muscle concerned. In the review of 35 studies, lip asymmetry and imbalance all resolved on their own⁴. For crow’s feet, the effect of a type A toxin has been shown for a median of 4 months⁵. The labels give no duration for the mouth and jaw, which are not approved indications. The page on how long botulinum toxin lasts explains what this duration depends on.

Is it reversible?

Yes. The effect of the toxin on muscles is temporary: transmission between nerve and muscle is gradually restored, first through small nerve sprouts, then by the return of the original nerve ending⁷. The smile regains its movement as the effect wears off.

Is there a treatment?

No product reverses the effect of the toxin: a smile that has changed but remains symmetrical corrects itself with time. Adding toxin elsewhere to "rebalance" only makes sense when there is an asymmetry, and this is decided during a consultation. No massage or exercise has shown any effect in the sources we consulted.

What should you avoid?

• Do not ask for another injection to get your smile back: muscle weakness can be made worse by another toxin injected before the effect of the previous one has worn off⁶.
• Do not judge the final result too early: the effect changes over the first few weeks, and for even longer after an injection of the masseters³.
• Do not try to compensate with other injectable products without medical advice.

When should you see a doctor?

Talk to the doctor who performed the injection if the change bothers you, if you have trouble opening your mouth, eating, drinking or speaking clearly, or if it does not improve. Dated photos, at rest and smiling, will help them judge how it evolves. Difficulty swallowing, a changed voice or difficulty breathing are warning signs: call emergency services (15 or 112 in France, or your local emergency number).

If one side of the smile lifts less than the other, the page on the asymmetric smile after an injection is more relevant. If the injection was meant to show less gum, see the page on the overcorrected gummy smile.