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

A forehead that creases on one side and stays smooth on the other, or lines that fade on one side only, are among the possible problems after a forehead injection. It is bothersome, because asymmetry draws the eye, but it is not dangerous and it is temporary. Reviews of the literature list asymmetry among the common adverse effects of botulinum toxin³. This page answers the seven questions people ask most often.

Why does the forehead become uneven after an injection?

The frontalis muscle has two halves, one on each side, and each lifts the eyebrow on its side. When one half is more relaxed than the other, the side that stays active keeps creasing and the forehead looks uneven.

A review of the complications of botulinum toxin in the upper face cites two main causes of asymmetry: a difference in the site or amount injected from one side to the other, and each patient’s own anatomical variations². Forehead muscles do not have the same shape, strength or position in everyone⁶. Some people have deeper lines on one side before any treatment: the same review describes asymmetrical line patterns, present in a small proportion of people². Softening the lines then makes an existing asymmetry more visible.

The labels describe this too: after treatment of the upper face with a type A toxin, facial asymmetry is listed among the uncommon effects¹.

How soon after the injection does it appear?

It becomes visible as the effect of the toxin builds up. For a type A toxin approved for the forehead, improvement of the lines is usually seen within 7 days of the injection, with the peak effect around day 30¹. The two sides do not always respond at the same pace: an asymmetry visible in the first few days may fade afterwards, or on the contrary become clearer.

How long does it last?

The asymmetry lasts as long as the effect of the product injected. With a type A toxin approved for the forehead, the effect has been shown for about 4 months after the injection⁴. Movement comes back gradually, and not necessarily at the same pace on both sides. Durations for each product are explained on the page about how long botulinum toxin lasts.

The short-acting botulinum toxin (serotype E) is approved only for frown lines, not for the forehead; its effect usually lasts 2–3 weeks⁵. It has been approved in the European Union since 15 July 2026 and in Canada since 22 June 2026^7,8.

Is it reversible?

Yes. An asymmetry caused by uneven relaxation disappears when the effect of the toxin wears off: each half of the frontalis muscle regains its strength. If the asymmetry existed before the injection, the forehead simply returns to how it looked before.

Is there a treatment?

Yes, in some cases. The principle is to rebalance the two sides by relaxing slightly the area that remains too active. The review mentioned above describes this correction for a common form of asymmetry, the eyebrow raised at the tail: adding a little toxin into the part of the muscle that remains active². The same logic applies to one half of the forehead that still creases. This procedure is decided after an examination, once the effect of the first treatment is complete: an asymmetry that is still changing is not corrected.

The doctor may also feel it is better to wait for the effect to wear off, for example if the asymmetry is slight or if a correction might relax the forehead too much. The label of a type A toxin states that intervals between two treatments should not be shorter than 3 months¹: an early small additional injection is a medical decision.

What should you avoid?

Avoid judging too early: wait until the effect is complete before drawing conclusions. Avoid having the asymmetry "compensated" by another practitioner without giving them the date, the area treated and the product used at the first session. Do not try to force the relaxed side with exercises: no exercise has shown any effect in the sources we consulted.

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 would help. See a doctor sooner if the asymmetry comes with an eyebrow or eyelid drooping enough to get in the way of your vision, or with visual disturbances. For this appointment, take photos from the front, with your forehead at rest and with your eyebrows raised, and bring the ones taken before treatment if you have them.

An uneven forehead often affects the eyebrows too: see the pages on uneven eyebrows after an injection and on the Spock brow, raised at the tail. If the forehead does not move on either side, the page on the frozen forehead is more relevant to you.