Botulinum toxins have a similar effect on the nerves to sweat glands that they do on nerves to muscles and so they are a very effective treatment for stopping the sweat glands under the armpit from working therefore stopping excessive underarm sweating.  This condition can be very awkward and embarrassing for many people and so this is a very popular and highly effective treatment option if hyperhidrosis, or excessive underarm sweating, is something that affects you.