Lower-Face and Neck Toxin: Where the Margin for Error Narrows
Upper-face treatment goes wrong cosmetically. Lower-face treatment goes wrong functionally, and that is the whole difference between them. The muscles below the mid-face are not decorative — they close the mouth, chew, articulate speech and hold the lower lip in place — and weakening them affects things the patient does all day.
This is why the region belongs after the upper face rather than alongside it, and why conservative assessment matters more here than technique.
What the region is genuinely good for
Masseter treatment has two quite different populations. One wants a softer lower-face outline; the other has bruxism, jaw pain or headaches and is seeking relief. Treating the masseter for those reasons is off-label across the EU, and the published evidence is limited and mixed rather than settled. It is still worth asking every patient which group they are in, because the assessment, the consent conversation and the measure of success all differ — and because off-label use carries its own consent and documentation duties.
Mentalis treatment addresses the dimpled, orange-peel chin produced by an overactive muscle, and is often more effective than filling the same area.
Depressor anguli oris treatment can lift a downturned mouth corner in the right patient. In the wrong one — where the corner is down because of volume loss and descent rather than muscle pull — it does nothing useful [2].
Platysma treatment softens vertical neck bands. It is worth being clear with patients that this addresses banding rather than laxity; skin that has lost elasticity is not a toxin problem and no amount of product will make it one.
The functional consequences
Over-treatment here does not look wrong so much as behave wrong. Excessive masseter weakening affects chewing, particularly of firm foods, and can alter the balance between the two sides. Diffusion toward the muscles around the mouth affects speech, the ability to purse the lips and, in some cases, control of a drinking glass. Difficulty swallowing is the recognised serious adverse event of lower-face and neck treatment, and it is the one that can require intervention rather than patience. Over-treated depressors produce a smile that is uneven in a way the patient notices in every photograph [3].
These resolve as the effect wears off. But "resolve" can mean several months of a change the patient encounters several times a day, and swallowing difficulty after lower-face or neck treatment is not a side effect to review in a fortnight — it is a reason to be seen urgently. A cosmetic result that is slightly under-treated is invisible; a functional result that is slightly over-treated is not.
Assessment that prevents most problems
Palpate rather than assume. Ask the patient to clench and feel what the muscle actually does — bulk, symmetry, which part is doing the work. Watch them speak and smile before deciding anything. Ask directly about previous treatment elsewhere, because the current state may be someone else's partially resolved result rather than a baseline.
In masseter treatment specifically, establish whether the concern is aesthetic, functional or both, and set expectations about timeline: visible change in facial outline develops over months rather than weeks, and patients told to expect it immediately conclude the treatment failed.
Who should not be treated
Botulinum toxin is a prescription-only medicine, and the decision to use it carries the contraindications of a drug rather than the cautions of a cosmetic. Disorders of the neuromuscular junction — myasthenia gravis, Lambert–Eaton syndrome, motor neurone disease — are contraindications, and their early presentations can be subtle enough that a new ptosis or a swallowing complaint deserves a diagnosis before it is treated. Medicines affecting neuromuscular transmission, aminoglycoside antibiotics among them, potentiate the effect. Treatment is avoided in pregnancy and breastfeeding, and postponed where there is infection at the intended site.
European product information for every licensed toxin carries a warning about effects spreading beyond the treatment site. Difficulty swallowing or breathing after treatment is an emergency, not a side effect to review at two weeks. None of this argues for hesitancy in appropriate patients; all of it belongs in the consultation and in the notes [1].
Principles
- Under-treat and review. This is true everywhere and it is not negotiable here.
- Treat symmetrically only if the muscles are symmetrical — many are not.
- Be conservative near the mouth. The muscles of articulation do not tolerate approximation.
- Distinguish muscle problems from volume and skin problems before reaching for toxin.
- Warn about function, not just appearance, during consent. Chewing, speech and smile symmetry belong in that conversation.
The training point
The lower face is where an injector's habit of conservatism is tested, because the patient often wants a dramatic change and the anatomy will let you deliver one. The practitioners who work here safely are the ones who arrived with the discipline already built — which is another argument for spending an unglamorous first year on the upper face rather than treating it as a formality on the way to something more interesting.