One part Dawn dishwashing liquid mixed with two parts HYDROGEN PEROXIDE. Add baking soda for scrubbing help. Use laundry brush to work into the stain. Supposed to actually take yellow armpit stains out of white shirts!
Use Hydrogen Peroxide to get rid of armpit stains, clean cookie sheets, as a miracle cleaner in the kitchen and bathroom - this stuff is amazingly versatile! The list goes on and on!This stuff is MAGIC