Botox: does it really stay where it's injected? What science says

Yes, botulinum toxin is a neurotoxin: that is precisely why it works

Let us start with the first point: yes, botulinum toxin is a neurotoxin. And that is precisely why it works. It penetrates the nerve endings of the treated area and temporarily blocks the release of acetylcholine, the chemical messenger that instructs the muscle to contract. It does so by cleaving a protein called SNAP-25, which is essential for vesicles to release that neurotransmitter at the neuromuscular junction.

The consequence is straightforward: the nerve transmits less of its signal to the muscle, and the muscle contracts less. That is the mechanism we are looking for when we treat, for example, forehead lines, frown lines, or what are commonly called crow's feet. This entire process — from binding to its receptors on the neuron to the cleavage of SNAP-25 — is very well described in the pharmacological literature.

Does it stay exactly at the millimetre where the needle enters? No

After an injection, there is a zone of local diffusion of the toxin's effect around the point of entry. This is something that those of us who administer injections know perfectly well. That diffusion is neither infinite nor random, but it does exist, and it depends on several factors: the dose used, the volume injected, the specific product, the depth, the anatomical location, and the injection technique.

That is why a botulinum toxin injection should not be considered a simple aesthetic gesture. Administering injections is not just about knowing how to handle a syringe: one must know exactly what is being injected, where it is being injected, and which muscles are in the surrounding area.

Why anatomy is almost everything

Let us take an example. When we treat the frown area, we want to act on certain muscles responsible for the lines in that zone. But just a few millimetres or centimetres away there are other muscular structures that we do not want to weaken.

If the injection is incorrectly placed, if the dose is inadequate, or if the diffusion reaches a neighbouring muscle, an unwanted effect may appear: an asymmetry, a change in the position of the eyebrow, or, in some cases, a temporary drooping of the eyelid. Precisely because the toxin has a zone of action around its point of entry, a precise knowledge of facial anatomy is indispensable.

And what about it 'travelling' through the nerves?

Here too there is a scientific reality that deserves a proper explanation. Various experiments, conducted mainly on animal and cellular models, have shown that a fraction of botulinum toxin can undergo retrograde axonal transport: that is, it can travel backwards through the interior of the nerve to more distant neurons. This is a truly fascinating phenomenon in neuroscience and one that continues to be the subject of ongoing research.

But going from that experimental observation to 'aesthetic injections travel to your brain and destroy your neurons' is a leap that the current data simply do not support. Changes in central nervous system activity have also been observed following certain injections in humans; however, that does not necessarily mean that large amounts of toxin have reached the brain. Some of those changes may be secondary to the modification of the sensory and motor information reaching the brain when a muscle's activity changes. Our brain continuously adapts to the signals it receives from the body.

Can there still be systemic complications? Yes.

And there is no point in hiding it. Medications based on botulinum toxin include — particularly in the United States — a prominent warning about the possibility of the toxin's effect spreading to distant sites. Symptoms such as generalised muscle weakness, difficulty swallowing, difficulty speaking, or, in exceptional cases, difficulty breathing have been reported, and these can appear hours, days, or even weeks after the injection.

These serious complications are rare, and their risk depends on the doses used, the indications, the patient's individual profile, and the conditions of use; the highest risk has been described in children treated for spasticity with high doses, not in aesthetic use at standard doses. Saying the risk is zero would be incorrect. But claiming the opposite — that every aesthetic injection causes chronic neurological toxicity — is equally wrong.

What about Alzheimer's disease, dementia, or ALS?

To date, we have no evidence to support the claim that aesthetic botulinum toxin injections cause Alzheimer's disease, dementia, or amyotrophic lateral sclerosis. Presenting that hypothesis as a proven consequence of the treatment goes far beyond the scientific data currently available.

So, should we be afraid?

No. But we should treat it with respect. Botulinum toxin is a biologically very active medication: it has indications, contraindications, doses, and potential adverse effects. The fact that an injection takes ten minutes does not make it a trivial procedure.

And that is probably the most important message I want you to take away: do not trivialise botulinum toxin, but do not demonise it either. When it is properly indicated, correctly dosed, and administered by a medical professional who has a thorough command of facial anatomy, it has a well-documented safety profile.

In aesthetic medicine, safety does not depend on the product alone. It depends, to a very great extent, on the person holding the syringe. I am Dr. Florian Vallecillo, and I will always prefer to explain the reasons behind something rather than frighten you with a headline or sell you the latest trend.