Botulinum toxin is a neurotoxin that helps control muscle spasms. It acts locally by blocking the release of acetylcholine (the neurotransmitter necessary to produce muscle contraction) and produces temporary muscle relaxation.
Botulinum toxin was first used at the medical level to treat blepharospasm (uncontrollable blinking) and strabismus (abnormal alignment of the eyes). In aesthetic medicine, it is used to relax the muscles that cause lines or wrinkles. Commonly treated areas of the face include the forehead, between the eyebrows, and the eye area known as "crow’s feet".