Hyperhidrosis is a common condition in which a person sweats excessively. When small doses of botox are injected into the skin, it blocks the signals from the nervous system that supply the sweat glands; this stops them working so hard and prevents them from producing so much sweat. After studies, Botox has been proven to reduce up to 95% of sweat in the injected area and can last between 6 - 12 months.