Key facts
- Class
- Prescription-only medicine, injected by a doctor after assessment
- Mechanism
- Blocks acetylcholine release at the neuromuscular junction, reducing the contraction that creates dynamic lines
- Directed at
- Lines produced by movement, muscle bulk such as the masseter, and excessive sweating
- Units
- Potency units are specific to each formulation's own assay and cannot be converted between brands
- Duration
- Temporary; the effect fades as nerve signalling recovers, and timing of any repeat is decided at review
What botulinum toxin is, and how it works
Botulinum toxin is a purified protein produced by the bacterium Clostridium botulinum. In the minute, measured doses used in medicine it blocks the release of acetylcholine, the chemical a nerve uses to tell a muscle to contract. The muscle that is injected relaxes in proportion to the dose; it is not paralysed in the sense people fear, and other muscles are unaffected unless product spreads to them. Over the following months the nerve forms new connections and movement returns.
It is a prescription medicine in Singapore and is injected by a doctor. Several formulations are registered, and each is measured in its own units, defined by that manufacturer's assay; a dose quoted for one brand cannot be converted into another. BTX is the site's shorthand for the class, not for any single brand.
How botulinum toxin is used in aesthetic medicine
Its first use is for dynamic lines: frown lines between the brows, horizontal forehead lines, crow's feet, lines across the nose, and the downward pull of the corners of the mouth or the vertical bands of the neck. These lines are made by movement, so reducing movement softens them. Dosing is calibrated to the muscle; the frontalis, for instance, is the only muscle that lifts the brow, so overtreating it drops the brow rather than smoothing the forehead. How this is planned is set out on the BTX treatment page.
Its second use is contouring. Injected into the masseter, it reduces the bulk of an overworked jaw muscle over weeks, which is why it is used for jaw slimming and for bruxism. The trapezius and calf muscles are treated on the same principle. Its third use is medical: it reduces sweating from the underarms, palms and soles in hyperhidrosis by blocking the nerve supply to sweat glands.
“If the line is there at rest, reducing muscle movement will not remove it.”
Dr Sin YongOn dynamic versus static lines
What botulinum toxin is often confused with
Botox is a brand name for one botulinum toxin product, in the way a brand of paracetamol is not paracetamol itself. The class includes several registered formulations, which differ in diffusion profile, onset and unit potency, and the choice between them is made for the zone and the patient.
The more consequential confusion is with dermal filler. Botulinum toxin treats the cause of a dynamic line by relaxing the muscle; it adds nothing. Filler treats the effect of volume loss by adding material. A forehead line that only shows on raising the brows is a BTX question; a tear trough hollow is a filler question. Using one where the other is indicated is a common reason for disappointment, and masseter treatment is sometimes confused with slimming the face in general, which it does not do.
When botulinum toxin is not the answer
If a line is visible at rest, it has become a crease in the skin, and reducing muscle movement will not remove it. Static lines need skin remodelling or filler, decided at assessment, and sagging driven by volume loss or descent is not a muscle problem at all. Lines that bother someone only in photographs under harsh light are sometimes better left alone.
As a prescription medicine it needs a doctor's assessment. It is generally avoided in pregnancy and breastfeeding, in neuromuscular disorders such as myasthenia gravis, with infection at the injection site and where there has been a previous reaction to any botulinum toxin product. Common side effects include bruising, headache and temporary heaviness of the brow or eyelid; asymmetry and spread to a neighbouring muscle are less common and settle as the effect wears off. These are discussed before any treatment, and the frozen look people fear is a sign of overdosing rather than of the medicine itself.
