Uneven lips after Botox: why, how long and what to do

A lip that lifts less on one side, a corner of the mouth that droops, a lower lip that no longer moves down in the same way when you speak: after a botulinum toxin injection around the mouth, the two sides do not always move identically. This is one of the most common lip problems after an injection. The asymmetry is mostly visible in movement, when you speak or smile, and less so at rest. It is temporary: most of the time it resolves on its own as the effect of the toxin wears off.

Why do the lips become uneven?

The lips are moved by many small muscles: the orbicularis, which runs round the mouth, muscles that lift the upper lip and the corner of the mouth, and others that lower the lower lip. It only takes the toxin acting a little more on one side, or reaching a neighbouring muscle that was not targeted, for the balance to change.

The sources describe several situations:

• injections around the mouth (perioral lines, "lip flip"): in a review of studies that included lines around the mouth, lip asymmetry and excessive weakness around the mouth were reported, the latter linked to the dose⁴;
• injections of the chin or the corner of the mouth: according to an expert consensus, an injection placed too far to the side, or spread to the muscle that lowers the lower lip, can make the lip uneven or droopy²;
• injections for crow’s feet: the label of a type A toxin recommends avoiding the area near the zygomaticus major muscle, which lifts the corner of the mouth, to prevent the lip from drooping³;
• injections of the nose: spread to the muscles that lift the upper lip can cause asymmetry or a drooping upper lip⁵.

In these situations, the mechanism described is the same: an effect of the product on the targeted muscle that is stronger than intended, or spread to a neighbouring muscle^2,5. Note that, apart from frown lines, crow’s feet and the forehead depending on the product, the French product labels provide for no aesthetic indication; lip injections are off-label⁹.

How soon after the injection does it appear?

It appears as the effect of the toxin builds up, usually in the first few days⁹. The US label of a type A toxin states that side effects usually occur within the first week⁸. No source gives a timeframe specific to the lips.

How long does it last?

It lasts at most as long as the effect of the toxin in the muscle concerned. In the review of 35 studies, all lip asymmetries resolved on their own¹. After a "lip flip", the problems described resolved within a few weeks⁶. The labels give no duration for the lips; for approved areas, the effect of a type A toxin has been shown for up to 4 months⁹. The details are on the page about how long botulinum toxin lasts.

Is it reversible?

Yes. The asymmetry disappears when the over-relaxed muscle regains its strength, as the effect of the toxin wears off. In the review of 35 studies mentioned above, none persisted¹.

Is there a treatment?

In most cases, you wait. When the asymmetry is bothersome, a correction may be considered: an expert consensus describes a small injection into the matching muscle on the opposite side, to rebalance the two sides², and a published case report describes an asymmetry corrected this way in two weeks⁷. This level of evidence remains low: a single case, with no comparative trial⁷. The decision rests with the doctor, after an examination. No massage, cream or exercise has shown any effect in the sources we consulted.

What should you avoid?

• Do not ask for a corrective injection too early, before the effect of the toxin has fully built up: the asymmetry can still change.
• Do not pile up injections: the effect of different toxins given a few months apart is not known, and weakness can be made worse by another toxin injected before the effect of the previous one has worn off⁸.
• Do not force certain movements to "rebalance": no source shows that exercises speed up recovery.

When should you see a doctor?

Talk to the doctor who performed the injection if the asymmetry bothers you, if you have trouble closing your mouth, eating or drinking, or if it does not improve. Dated photos taken at rest and smiling will help them track how it evolves. Difficulty swallowing, a changed voice or difficulty breathing, on the other hand, are warning signs that mean calling emergency services (15 or 112 in France, or your local emergency number).

If the asymmetry follows a "lip flip", the page on a lip flip gone wrong details the problems specific to this technique. If it is mainly your smile that goes crooked, see the page on the asymmetric smile after an injection.