Botulinum toxin works by relaxing specific muscles under the skin to treat facial wrinkles. In some instances it can also be used to treat bulky muscles like the masseter (jaw) to give a slimmer appearing face. Botulinum toxin can also be used to treat excessive sweating for example under the arms. Botulinum toxin has been used in the medical field for over 3 decades and therefore has a very good safety profile.