New research has uncovered disturbing findings that Botulinum neurotoxin type A, which is otherwise known as botox, has the ability to travel from the injection site to the brain.
In the study, researchers injected rats' whisker muscles with botulism - the toxin commonly used to treat muscular disorders and in cosmetic procedures.
Then, they looked at the connected brain areas for a tell-tale sign of the toxin: the remnants of a protein that botulinum breaks down.
Three days after the injection, they found these remnants in an area in the brainstem. The dilute amount of the toxin that reached these cells meant that there were no noticeable effects on the animals.
The fact that the toxin gets inside nerves allows it privileged access to the brain, which blood-borne drugs often have trouble reaching, reports Nature.
This previously unknown ability of botilinum to affect the brain "is certainly of concern", said Matteo Caleo of the Italian National Research Council's Institute of Neuroscience in Pisa, who reports the work.
The result shows that more work is needed to better understand how the toxin spreads along nerves, and how to prevent this or use it to therapeutic benefit, said Caleo.
The study is published in the Journal of Neuroscience.