Botulinum toxin is a protein which is produced by the bacterium Clostridium botulinum. It interferes with neuron transmission, which can keep muscles from contracting. As this effect can be very deadly, botulinum toxin is known as a neurotoxin, meaning that it is a toxic agent which affects the nervous system. When used in small amounts and in highly localized applications, however, it can be extremely medically useful to treat uncontrollable muscle spasms in conditions such as torticollis and spasmodic dysphonia. The most publicized use, however, is purely cosmetic: it can be used to smooth out facial wrinkles, and for this use it is often known by the trade name Botox.