Botox is Botulinum toxin A, a muscle relaxant that is injected into the muscles or deep into the skin. It works by partially blocking the nerve impulses to any muscles that have been injected and reduces excessive contractions of these muscles. In the case of chronic migraine, it is thought that Botox blocks pain signals, which indirectly block the development of a migraine. When injected into the skin, Botox works on sweat glands to reduce the amount of sweat produced. When injected into the bladder wall, Botox works on the bladder muscle to prevent leakage of urine (urinary incontinence) due to uncontrolled contractions of the bladder muscle.