Botox works by blocking the nerves responsible for activating your sweat glands. Normally, your nervous system activates your sweat glands when your body temperature rises. This is how your body automatically cools itself. In people with hyperhidrosis, however, the nerves that signal the sweat glands are overactive.
When you receive Botox injections directly into the area of your body that commonly sweats, your overactive nerves are essentially paralyzed. When your nerves can’t signal your sweat glands, you don’t sweat. However, Botox only prevents sweating in the specific area where it’s injected. Botox injections are very shallow, meaning that the medicine is injected just below the surface of the skin, where it remains.
When used to treat underarm excessive sweating, Botox has been shown to result in an 82-87% decrease in sweating. Results start to be noticeable approximately 2 to 4 days after treatment with the full effects usually noted within 2 weeks. Dryness typically lasts 4 to 12 months but some studies have found it can last as long as 14 months.