Open before and after gallery. Botulinum toxin works by relaxing specific muscles under the skin in order to treat facial wrinkles, improve facial symmetry and proportion and reduce bulky muscles such as the masseter. Botulinum toxin has been used in medical treatments for over 4 decades and was first approved by the Food and Drug Administration (FDA) for the treatment of wrinkles in 1989. It is now one of the most popular cosmetic treatments in the world.