I once read that (not in alle cases) Teatree oil can help. The bacteria producing the bad smell seem not to like the oil. Teatree oil is cheap en easily to buy. I've got sometimes troubles with bad smell, especially when I transpire hard. The Teatree oil helped, although you have to renew the treatment after a month or two. I just brought the oil in the armpit for a day of 5 and the problem was gone. As Teatree oil costs almost nothing, it 's worth a try.