i have a friend who has suffered all of his life with very smelly feet. So much so that his wife amkes him put his socks in a lidded nappy bucket when he takes them off, and they have to be washed seperately from the rest of the household washing, otherwise everthing comes out smelling slightly of feet. He tried all the normal things - erall leather shoes, cotton socks, lots of washing, trips to Drs about it. For a long time there was no answer.
Then he had a medical at work, where the problem was noted (you could hardly miss it!). They got the Dr to prescribe some cream (anti fungal????) and the problem has pretty much gone.
This rambling is probably just to say that if it is a problem tkae him to the Drs and get it checked out - there could be some sort of foot infection making it occur.