When botulinum toxin is injected into the muscle, it spreads to the nerve terminal and prevents a neurotransmitter from releasing, stopping muscle activity. This site-specific paralysis smoothes wrinkles and stops spasms. Botulinum toxin also prevents the release of pain and inflammatory mediators - an effective way to treat migraines.

But the effects of botulinum toxin wear off. The nerves take about 120 days before it regenerates, explaining why people sometimes get serial treatments.

Belgian scientist Emile Pierre van Ermengem discovered Clostridium botulinum after a botulism outbreak in Belgium. In the 1920s, scientists tried to isolate botulinum toxin, but it took another 20 years before it was isolated in crystalline.

In the 1970s, scientists tested a treatment for strabismus (crossed eyes) on monkeys and noticed reduced wrinkles in the skin between the eyebrows and above the nose. After the toxin proved successful, Allergan licensed the treatment and branded it Botox.