Miracle stain remover: 1 part blue Dawn dishwashing liquid, 2 parts hydrogen peroxide. If bad use old toothbrush & baking soda to scrub it in & let sit for an hour before washing. Works on every stain from set in grease, to yellow arm pit stain.
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!
MS: DIY Underarm Stain Remover: 1 part Dawn (or any dishwashing liquid, I assume), 2 parts hydrogen peroxide, then add baking soda to create a paste. Use brush to work it in, and let it sit for 1 hour.