The short answer, and why it is a range
Anti-wrinkle injections typically start showing an effect within three to five days, reach their full effect by about two weeks, and fade gradually over roughly three to four months. It is a typical range, not a guarantee for any individual face, because dose, the muscle involved, and simple biological variation between people all move the number in either direction.
The mechanism behind the softening itself, how botulinum toxin blocks the nerve signal at the neuromuscular junction so the muscle stops folding the skin above it, is covered in full in how anti-wrinkle injections actually work. This piece starts where that one stops: not what the treatment does, but the clock it runs on, and why that clock does not tick the same way for everyone.
Onset: why nothing changes on day one
The toxin has to reach the nerve ending, be taken up into it, and then act on the machinery inside that releases the chemical messenger which tells the muscle to contract. None of that is instant. Most people see the first softening from around three to five days after treatment, with the effect continuing to build until it is fully developed by about two weeks.
Jawline slimming from masseter treatment runs on a different, slower curve again, because that change is not just the nerve signal quietening. It also depends on the muscle itself gradually reducing in bulk once it stops working as hard, which plays out over the weeks that follow rather than settling by the two-week mark the way a frown line does. Judging either outcome before that window has passed is judging an unfinished result.
Why it wears off: a handover, not a switch
The wearing-off is not the nerve simply "waking back up" on a set date. Research on this exact mechanism, published in the Proceedings of the National Academy of Sciences, found that once a nerve ending is blocked, it responds by growing temporary side branches, called sprouts, that reconnect with the muscle and carry the earliest return of movement. The original nerve ending is still recovering underneath while these sprouts are doing the work. Only once the original ending resumes normal signalling on its own are the temporary sprouts withdrawn.
That two-step process, sprouts first, original ending later, is why the fade reads as gradual and sometimes slightly uneven rather than a single day where the effect simply stops. A line that seems to soften back in patches over a few weeks is usually this handover in progress, not a sign anything went wrong.
What actually moves the number: dose, muscle, area, the person
Four things account for most of the variation from one person, or one area, to the next.
Dose is the most direct lever: a higher dose generally takes longer to fully wear off than a lower one in the same muscle, which is one reason a conservative starting dose is not a compromise, it is a deliberate first data point on how a particular face responds.
Muscle bulk and strength matter because a stronger, larger muscle has more work to do to overcome the same degree of blockade, and a masseter treated for jaw slimming is a different proposition from the smaller muscles around the brow. A comparative study of botulinum toxin across both facial-wrinkle and masseter treatment found the two outcomes did not behave identically over time even within the same toxin types, which is consistent with area and what is actually being measured, a line softening versus a muscle's bite force, mattering as much as the toxin itself.
Area follows from the same logic: a muscle used constantly, such as one involved in a habitual expression or in clenching, is re-exercising itself throughout the recovery window in a way a quieter muscle is not, which can shift how quickly function is felt to return even if the underlying nerve recovery timeline is similar.
And the person is the variable that resists a number altogether. Metabolism, the density of nerve endings in an individual's muscle, and simple biological variation between people all play a part, which is exactly why this article gives a typical range rather than a fixed figure, and why the honest position on any one face is to observe how it responds rather than assume it will match the average.
The rare complication: antibody resistance
A small number of people develop neutralising antibodies against the toxin, which make subsequent treatments progressively less effective even at doses that worked well before. This is worth naming honestly rather than leaving out, and it is also worth putting in proportion. A 2024 literature review on the immunogenicity of botulinum toxin type A across both clinical and cosmetic use found that aesthetic treatment uses lower doses than therapeutic use, and that treatment failure from antibody formation is uncommonly reported at cosmetic doses, while cumulative dose, number of treatment cycles, and how frequently injections are given were the factors most associated with raising the risk. The same review noted a caution worth keeping rather than dropping, that antibody incidence in aesthetic use specifically may be underreported, since most people who stop responding well simply stop coming back rather than being formally investigated.
In practice, this argues for spacing treatments by how the muscle has actually recovered rather than compressing them closer together than necessary, which is the same principle the next section covers from a different angle.
Why an early top-up is not the answer
Someone who notices one side softening slightly ahead of the other, or the effect seeming to fade a little sooner than last time, may wonder about an early top-up to smooth it out. The more useful answer is usually to wait rather than add more toxin sooner than the muscle has actually finished its cycle.
Two reasons sit behind that. First, an uneven fade during the handover described above is common and typically settles on its own within a short period, so treating it as a fault to be corrected often means correcting something that was never wrong. Second, adding toxin into a muscle before its previous dose has genuinely worn off raises the cumulative dose delivered over a given stretch of time, and cumulative dose and injection frequency are exactly the factors the literature above ties to the rare cases of resistance. Spacing repeats by response rather than by impatience protects both the result and the long-term reliability of the treatment.
How repeat timing is actually decided
At this clinic, repeat timing is planned around how the muscles have responded since the last treatment, assessed at review, rather than booked automatically for a fixed number of months ahead. Movement returning is the expected, planned end of one cycle, not a sign the treatment failed or that something was done wrong the first time. Nothing rebounds beyond the original baseline, and nothing is made worse by letting the effect run its full course before deciding on the next one.
That review is also where dose gets reconsidered, not just the date. A face that has settled into a comfortable pattern over a few cycles sometimes needs less than the first treatment did, and occasionally more, and that decision belongs in an assessment rather than a standing calendar entry. Which line type responds to which treatment class in the first place is the earlier decision this same kind of assessment makes, before duration ever becomes the question.
