Smile problems after Botox: uneven, changed, overcorrected

The smile involves several small muscles that pull on the lips and cheeks. An injection of botulinum toxin near the mouth, or at the corner of the eyes when crow’s feet are treated, can relax one that was not targeted. This page is part of our guide to problems after an injection, organised area by area.

What problems can affect the smile?

Three situations are presented: an asymmetric smile, when one corner of the mouth lifts less than the other; a changed smile, less natural or less wide than before; and an overcorrected gummy smile, when the injection meant to show less gum relaxes the upper lip too much. The asymmetric smile is also listed under the eye area, and the changed smile under the jaw area, because the injection involved may have been given there.

The labels describe this mechanism: when treating crow’s feet, one type A toxin advises avoiding injections too close to the zygomaticus major muscle, which lifts the corner of the mouth, to prevent the lip from drooping¹. Facial asymmetry is also among its uncommon effects¹. For the gummy smile, a small pilot study in five patients treated the muscles that lift the upper lip; the improvement lasted 3 to 6 months³. This small number of patients shows that data on this use remain limited.

Each page details the cause, when it appears, how long it lasts and what can help.

Which signs mean you should see a doctor quickly?

A slightly asymmetric smile is bothersome but not dangerous: it returns to normal as the effect of the toxin wears off. See a doctor promptly if you have trouble keeping liquids in your mouth, eating or speaking clearly, or if the lip droops noticeably. Any difficulty swallowing, speaking or breathing means calling emergency services (15 or 112 in France, or your local emergency number): the labels describe these as the rare signs of the toxin spreading away from the injection site, which require immediate medical care^1,2.

Before seeing a doctor, write down the date of the injection, the areas treated and the day the problem appeared. If possible, contact the doctor who performed the injection.

Why are injections given near the smile?

Injections near the smile mainly target the so-called gummy smile, when the upper lip rises enough to show a large area of gum: relaxing the muscles that lift the lip reduces this display³. This indication does not appear in any French label: type A toxins have aesthetic indications limited to frown lines, crow’s feet and forehead lines, depending on the product⁴, and the short-acting botulinum toxin (serotype E) to frown lines only², approved as of 9 October 2026 in the European Union and Canada^5,6. It is therefore an off-label use. To understand why and how a gummy smile is treated, see the page for this area in our atlas of treatment areas.

If your problem mainly affects the shape of your lips, see the page on lips after an injection; if it followed a crow’s feet injection, the page on problems at the corner of the eyes.