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

After an injection, one eyebrow sometimes ends up slightly higher or lower than the other. The difference may be only a few millimetres, but it shows, because the eyebrows play a big part in facial expression. Uneven eyebrows are among the eyebrow problems after an injection: a review of the literature lists asymmetry among the common adverse effects of botulinum toxin³. This effect is temporary. This page answers the seven questions people ask most often.

Why do the eyebrows become uneven after an injection?

The height of each eyebrow depends on the balance between the forehead muscle, which lifts it, and the muscles between the eyebrows and around the eye, which lower it¹. If this balance of forces is not changed in the same way on both sides, the two eyebrows no longer sit at the same height.

A review of the complications of botulinum toxin in the upper face describes two main causes of uneven eyebrows: a difference in the site or amount injected from one side to the other, and the patient’s anatomical variations¹. A common form is the eyebrow raised at the tail, known as the Spock brow or Mephisto sign: the outer part of the forehead muscle, which stayed active, lifts the eyebrow tail¹; it can affect one side only. Conversely, stronger relaxation on one side can make that eyebrow drop.

The labels describe this effect too: after treatment of frown lines with a type A toxin, eyebrow asymmetry is listed among the uncommon effects².

How soon after the injection does it appear?

It appears as the effect of the toxin builds up. With a type A toxin, first effects are usually seen within 2–3 days, with the peak effect at day 30 for frown lines². With the short-acting botulinum toxin (serotype E), first effects appear from 8 hours and the peak effect is reached around day 7⁵. The two sides do not always respond at exactly the same pace: a slight asymmetry in the first few days can fade once the effect is complete.

How long does it last?

As long as the effect of the product injected. With a type A toxin, the effect on frown lines has been shown for up to 4 months⁴. With the short-acting toxin, the effect usually lasts 2–3 weeks⁵. This toxin has been approved for frown lines in the European Union since 15 July 2026 and in Canada since 22 June 2026^6,7. The page on how long botulinum toxin lasts explains these durations product by product.

Is it reversible?

Yes. When the effect of the toxin wears off, the muscles regain their strength and the balance between the two sides returns. If the asymmetry existed before the injection, the eyebrows simply return to their original position.

Is there a treatment?

It depends on the direction of the asymmetry. When an eyebrow is too high, especially in its outer part, the correction described consists of adding a little toxin into the part of the forehead muscle that remains active, on the side concerned¹. When an eyebrow is too low, the forehead muscle cannot be given back its strength; the doctor may discuss a procedure on the muscles that lower this eyebrow. The review cited indicates that treating the orbicularis muscle of the eye lifts the eyebrow tail, and treating the frown line muscles lifts its inner part¹.

These procedures are decided after an examination, once the effect of the first treatment is complete. The doctor may also advise waiting, if the asymmetry is slight. No dose is given here: the units of different toxins are not interchangeable⁵.

What should you avoid?

Avoid judging the result too early. Do not have the asymmetry corrected by a practitioner who does not know about the previous session. Do not shorten the interval between sessions without medical advice: the label of a type A toxin states that intervals between two treatments should not be shorter than 3 months². After a short-acting toxin, a type A toxin injected less than 30 days afterwards has not been evaluated⁵.

When should you see a doctor?

Talk to the doctor who performed the injection if the asymmetry bothers you once the effect is complete, to find out whether a correction is possible and when. See a doctor sooner if one of the eyebrows or eyelids droops enough to get in the way of your vision, or if your vision is blurred or double. Take photos from the front, at rest and with your eyebrows raised, and bring the ones taken before treatment if you have them.

Depending on the form of the asymmetry, see also the page on the Spock brow raised at the tail, the one on the eyebrow that droops, or the one on the uneven forehead, which often goes with it.