Neuromodulators, fillers and biostimulators: what each one does

Three categories of injectable account for most of what happens in a medical-aesthetics clinic, and they are routinely confused — including in the way they are advertised. They work by entirely different mechanisms, they last for different lengths of time, and they solve different problems. Knowing which is which makes you a considerably better-informed patient.

A neuromodulator — botulinum toxin type A, sold as Botox, Dysport, Xeomin and others — is a purified protein that temporarily reduces the signal from nerve to muscle. Injected in tiny quantities into a specific muscle, it reduces how forcefully that muscle contracts. It adds no volume. It does nothing directly to the skin. Its entire effect is on movement.

That makes it the right tool for dynamic lines: horizontal forehead bands, the vertical glabellar elevens, crow's feet, and a range of smaller applications such as a gummy smile, a downturned mouth, jaw clenching and excessive sweating. It is the wrong tool for a hollow temple or a deflated cheek.

Onset is gradual — three days to see something, ten to fourteen for the full effect — which is why we review at two weeks rather than judging on day three. Duration is typically three to four months and varies with dose, muscle strength and metabolism. Common effects are pinpoint bruising and a mild headache for a day. The uncommon ones — a heavy brow, an asymmetric smile, a drooping eyelid — are almost always product diffusing where it was not wanted, they are temporary, and they resolve as the effect wears off.

A dermal filler is a gel, usually hyaluronic acid, that occupies space. It is the right tool for volume: structural support on bone in the cheek or jaw, softening a fold, defining a lip border, filling a tear trough in carefully selected patients. Different products have different densities and are chosen for the layer being treated. The result is immediate, though swelling means the honest verdict comes at two weeks.

Fillers last longer than neuromodulators — roughly six to twelve months in the lips, twelve to eighteen in the mid-face — but lasting is not the same as disappearing. Filler degrades unevenly, and repeated treatment before full resorption is how faces slowly become overfilled without anyone deciding to overfill them. This is the most common reason we decline to treat someone on the day.