Frozen face after botulinum toxin: myth or reality?

Where does the frozen look come from?

Botulinum toxin type A relaxes, for a few months, the muscle into which it is injected. At the right dose, it softens an expression line without removing movement. The face looks frozen when the effect is too strong, or when it reaches a muscle that should not have been affected.

International recommendations have moved in this direction. The aim is no longer to paralyse the muscle, but to modulate its activity, with lower doses in the upper face. Experts also note that overcorrecting one area harms the whole: the look becomes unnatural, and neighbouring muscles may start to compensate.

Three situations that create a frozen look

• A dose too strong for the muscle. Movement disappears instead of softening: the forehead becomes smooth, but motionless.
• The forehead treated alone. The forehead muscle is the only one that lifts the eyebrows. If it is relaxed without taking into account the frown muscles, which pull the eyebrows down, the eyes can look heavy. The risk is greater when the eyebrows are naturally low, as is often the case in men, or when the forehead is already working constantly to hold them up.
• An eyebrow lifted too high. When only the centre of the forehead is relaxed, the outer part of the muscle, still active, can pull the tail of the eyebrow upwards: this is the so-called "Mephisto" effect. One product's instructions list it among the common effects after treating the frown. A small additional injection usually corrects it.

These effects are temporary: they fade with the product. But once injected, the toxin cannot be removed. An effect that is too strong can only wait, or sometimes be balanced by treating the opposing muscle.

When the effect appears, and why the dose varies

The first effects appear within two to three days. The result is largely in place at around two weeks, even though the product instructions place the maximum effect at around one month. The muscle then gradually regains its strength, over three to four months on average.

The dose depends on the strength and size of each muscle, which vary greatly from one person to another. Men have, on average, more muscle mass: in a trial of one toxin, effectiveness was lower in men at the usual dose, and an expert consensus proposes higher doses for them. The same dose can therefore be too low for one person and too strong for another.

"The product builds up": true or false?

False. The toxin blocks the signal between nerve and muscle, then the nerve ending restores its connections: according to one product's instructions, recovery normally occurs within about twelve weeks. Each session works for a while, then wears off.

A retrospective study looked at 945 patients who had received at least three sessions, more than 4,000 treatments in all. Doses remained stable from one session to the next, no cumulative side effect was observed, and side effects even became less frequent over the sessions.

One nuance: after several sessions, the effect sometimes lasts a little longer. This is not product stored in reserve, but a more lasting response of the muscle. Sessions can then be spaced further apart.

"Lines come back worse when you stop"?

None of the studies I have reviewed describes such a rebound. When the effect fades, the muscle gradually regains its strength and the face returns to how it was before. What can be surprising is the contrast: you got used to a smoother forehead, and time, meanwhile, has kept passing. The limited data suggesting even the opposite are discussed in my article on the age to start.

"The muscles waste away"?

Here, the belief contains some truth. A reduction in muscle volume has been described after repeated injections, especially at high doses. It is even the intended effect when slimming an overly thick masseter. One product's instructions list it among the effects reported since marketing, without giving its frequency.

The available publications describe it as temporary and reversible once treatment stops. But it remains poorly studied, and the trials behind one product's instructions did not assess repeated sessions beyond one year. This is one more reason for measured doses and well-spaced sessions.

"Over time, you become resistant"?

It is possible, but rare. The body can produce so-called neutralising antibodies, which make the toxin less effective. The product instructions state that doses that are too high or too close together increase this risk. I therefore keep at least three months between two sessions and avoid repeated touch-ups. In the study of 945 patients, nothing pointed to a loss of effect over the sessions.

How I work

• I observe your face at rest and in movement, and analyse it by computer before choosing the muscles to treat.
• I think in terms of balance: the forehead is not treated without looking at the frown and the position of the eyebrows.
• I start with a cautious dose and deliberately keep some movement. More can be added at the check-up around day 15; nothing can be taken away.
• I keep at least three months between two sessions.

The toxin is not used during pregnancy and breastfeeding, in the case of a neuromuscular disease such as myasthenia gravis, or if the area is infected. It only works on lines caused by movement: a hollow or a line that is marked at rest calls for other approaches, which we can discuss together. And keeping your lines remains an entirely legitimate choice.