Botulinum toxin vs dermal fillers:
which does what, and when both

What is the difference between botulinum toxin and a dermal filler?

Botulinum toxin acts on muscle; a dermal filler acts on space. Botulinum toxin is a prescription medicine injected into a specific muscle, where it blocks the signal that makes that muscle contract, so the skin above is folded less often and less hard. The page on botulinum toxin sets out the muscles treated and the two categories of use. A dermal filler is a gel, most often hyaluronic acid, placed in a chosen tissue plane to occupy volume that has been lost or was never there.

Because the mechanisms are unrelated, the two are not alternatives for the same problem. A line that appears only when you frown is a muscle problem. A hollow under the cheekbone is a volume problem. Both show up as shadows in the mirror and both arrive in a syringe, which is where the confusion starts; dermal fillers do not relax a muscle, and toxin does not add a millimetre of volume.

Which lines need toxin, and which need filler?

Lines that appear with expression and fade at rest need toxin; folds and hollows that are present at rest usually need volume or structure, and sometimes skin treatment. Frown lines, horizontal forehead lines and crow's feet are made by the frontalis, the glabellar complex and the orbicularis oculi contracting thousands of times a day, which is why forehead and frown lines respond to muscle relaxation while the muscle is still the cause.

The nasolabial fold is the clearest example on the other side. It is a structural crease where the mobile cheek meets the fixed upper lip, deepened by cheek fat that has deflated and descended, so relaxing a muscle does nothing for it. Nasolabial folds are assessed from the cheek above, and support is restored there before the line itself is considered. A short chin, a flat temple or a hollow tear trough are also volume questions, not movement ones.

The overlap sits in the middle: a frown line that has been folded for so long that it is etched into the dermis at rest. Toxin stops the folding; it does not fill the groove that is already carved. That groove may need skin remodelling or, in careful hands and with full awareness of the vascular risk of the glabella, a small amount of filler. Which applies is decided by looking at the line at rest and in movement, not from a photograph.

“A filler adds volume. It does not lift, and it does not tighten. Asking it to do either is how faces end up over-filled.”

Dr Sin YongOn what a filler cannot do

When are botulinum toxin and filler planned together?

Toxin and filler are planned together when a face has both a movement problem and a volume problem, which after the mid-thirties is common. The lower face is the usual example. Botulinum toxin into the depressor anguli oris eases the downward pull at the corners of the mouth, while filler or a biostimulator restores the structure of the chin and pre-jowl area that lets the corner sit level.

Sequence matters. Where both are planned in one area, toxin is often placed first and the face reviewed after it has taken effect, because a relaxed muscle changes how much volume, if any, is still needed. In the upper face, a forehead that was working hard to hold heavy brows up is examined before anything is injected, since relaxing it fully can drop the brow. Volume restoration in the temple can change how the brow reads before any muscle is touched.

A combination is not the same as more. Each product is dosed to what the examination finds, and the aim is a face that still moves. Published comparisons of toxin alone against toxin with hyaluronic acid filler in the glabella address the etched component that toxin leaves behind; that is an argument for assessing the line at rest, not for adding filler routinely.

Can either be reversed if the result is not wanted?

Botulinum toxin cannot be reversed, but it wears off as the nerve endings recover, so an unwanted effect is temporary by nature. Hyaluronic acid filler can be dissolved with hyaluronidase, in a targeted way, and that is the reason it is the usual first choice for anyone new to filler. Calcium hydroxylapatite, polycaprolactone and poly-L-lactic acid cannot be dissolved; they are placed conservatively and in deep planes for that reason.

The two also fail differently. Too much toxin in the wrong muscle produces a heavy brow, an asymmetric smile or a frozen upper face until the effect fades. Filler placed in the wrong plane, in too great a quantity, or layered over product that has not yet cleared produces heaviness and a loss of contour, and the serious risk with any filler is a blocked blood vessel. The dermal fillers page describes the warning signs and why hyaluronidase is kept in the room wherever hyaluronic acid is injected.

Who should wait, and who assesses which is needed?

Both are deferred in pregnancy and breastfeeding, and where there is infection or inflamed skin at the site. Toxin is avoided in neuromuscular disorders such as myasthenia gravis and reviewed where medicines affect nerve transmission; filler is discussed carefully where there is a bleeding tendency, autoimmune disease, a keloid tendency or earlier non-resorbable product. Neither suits loose, redundant skin, which is assessed for lifting or referred to a plastic surgery specialist.

The assessment is the same for both: the face is examined at rest and in animation, the muscles are watched working, and the volume of each compartment is compared with the skeleton beneath it. Dr Sin Yong, an aesthetic physician, performs that examination and the injections himself. The fee follows what the examination finds, including the areas treated, the formulation or material and the quantity the anatomy calls for; how fees are quoted explains the written itemised quote given after consultation, since Singapore's advertising rules prevent prices being published.