Axillary Hyperhidrosis: Botox Cosmetic is FDA approved for excessive underarm perspiration that is not adequately managed with topical agents. Botox® neurotoxin treatment helps control this condition by temporarily blocking the chemical signals from the nerves that stimulate the sweat glands. When the sweat glands don’t receive chemical signals, the excessive sweating stops. You should notice a significant reduction in underarm sweating within 4 weeks of your first treatment and results should last up to 6-8 months.