What Causes Sweating At The Night Time?

my husband sometimes sweats profusely at night, completely soaking the bed. Even worse than the wetness is the smell. it smells like something fermenting, maybe yeast. It is extremely foul. His brother also does this (according to his wife). Its not every night, but the smell is so pungent, our mattress is disgusting. I change the sheets regularly & use febreeze on the mattress, let it air out, etc. His pilllow also gets drenched. even the stains are terribly embarrasing. What can we do to help this. I cant stand to sleep in our bed anymore.