Antiperspirant deodorants often claim to offer "24-hour" protection. What determines the length of time a deodorant works and how do they test for it? How does the chemical composition of the deodorant prevent perspiration?

Rowan Howell Lewes, East Sussex, UK

I understand that anitperspirants work by plugging skin pores with aluminum salts.  But it does not seem that blocking excretion of a substance would prevent the body from producing it. I envision blisters or cysts forming under the skin,perhaps merging to form a layer of somewhat nasty fluid.  In my case at least, huge volumes of the stuff would accumulate.  So what really happens?