Accurately speaking, alum soaking feet is not antiperspirant, but antiperspirant. Alum has a strong adsorption capacity, which can adsorb your beriberi. After soaking your feet, a small amount of alum will adhere to your feet. When your feet sweat, it will absorb the smelly substances such as urea in your sweat, so you can stop sweating!
I think you should know that activated carbon insoles also have this effect! The principle is basically the same, except that activated carbon can't be attached to feet, but can only be made into insoles!