Aluminum chloride hexahydrate
"Drysol is one of those rare cases where the product works exactly as advertised. The first day I used it, I already saw a dramatic difference in my sweating. And I am not talking just a little bit less sweat, I am talking literally none. Application is as simple as putting it on before you go to bed (a few dabs on each armpit) and then showering in the morning.

Now, there are two small flaws to this product:

1. As some others had mentioned, Drysol can be a little irritating to the skin. The applied area might sting a little or be itchy, but it's nothing terrible.

2. Because Drysol is essentially closing the pores in your armpits to achieve results, this does lead to more sweating in some areas, if you have heavy forehead/back sweat."