Excessive sweating, or hyperhidrosis, is caused by stimulation of the sweat glands by nerve endings which descend from higher centers in the brain. These nerves respond to emotional stresses; like intimate social situations, public speaking, physical stresses, and increased body temperature that comes with exercise or hot humid weather.
Most people with excessive sweating are bothered primarily when they are emotionally stressed, physically active, or over-heated. Botox can prevent sweating for months by blocking the release of the neurotransmitter, i.e., acetylcholine, from the nerve endings, that causes the glands to produce sweat.