Three to four months is not marketing — it is how long nerve terminals take to regrow. Here is why yours may fade sooner and what improves with repetition.
Botulinum toxin blocks the signal between nerve ending and muscle. The block itself is not undone; instead the nerve grows new terminals around it, and that regrowth takes roughly twelve to sixteen weeks. That is the mechanism behind the three-to-four month figure, and it is why no injector can make a standard dose last a year. Anyone promising six months from one session is either overdosing you or counting the fade-out as effect.
Muscle mass is the biggest single factor: a heavy frontalis or a strong masseter needs more units to reach the same effect and recovers sooner. Regular endurance training and a high metabolic rate shorten duration measurably. First treatments also fade faster than later ones, because untrained muscle is stronger. Men typically need twenty to thirty percent more units than women in the same area for the same result — that is anatomy, not pricing strategy.
By the second or third cycle the treated muscle has partly weakened from disuse, so the same result needs fewer units and holds a few weeks longer. More importantly the static line — the crease still visible when your face is completely still — starts to soften, because the skin is no longer being folded a thousand times a day. That is the real long-term argument for treating early and lightly rather than late and heavily.
Two rules protect the result. Review at day fourteen, not day five: the effect is not fully in yet, and topping up early is how eyebrows end up uneven. And leave at least three months between full sessions, because frequent small doses raise the theoretical risk of neutralising antibodies and, in practice, blur where you are in the cycle. If it has faded at ten weeks, the answer is more units next time, not another session now.
No. The muscle regains its original strength and the lines return to where they would have been anyway — no worse, no faster. The idea that stopping causes a rebound is a myth.
That depends on your lines, not your age. If a crease is visible when your face is at rest, treating it now stops it deepening. If it vanishes completely at rest, there is nothing urgent to treat.