I read somewhere that smelly feet could be sign of a zinc deficiency. Don't know if that applies to underarms.
My aunt had this problem and she called me about it. She used Head and Shoulder, which has zinc as an active ingredient, and I told her to use that to wash her underarms, and then to put on Colloidal Silver . She said it really worked.
FYI, the castor oil/iodine mixture works great for me, underarms.