May be worth trying this. Baby Powder as Stain Guard Sprinkle a little on the shirt’s underarms and collar, then iron to prevent sweat stains on white shirts. The powder forms a barrier that keeps oil and grime from seeping into the threads.
Recipe: 1 part Dawn dishwashing liquid 2 parts Hydrogen Peroxide Mix, pour on stains and scrub with a laundry brush. Add baking soda for a little grit, and there you have it! After letting it sit a while, put it in the washer and wash as usual.
stubborn grease stains and armpit stains 5 The mixture I scrubbed on with the brush above was 1 tsp. Dawn dishwashing detergent, tablespoons of hydrogen peroxide, and a couple tablespoons of baking soda.
---every girl need to remember this for their guy! Remove yellow underarm stains--Mix hydrogen peroxide and baking soda. Apply to stains, let soak for 30 minutes and wash like normal. - I've gotta try this. I have a couple shirts def worth saving
The armpit stain removal trick requires mixing just one part dishwashing liquid with two parts hydrogen peroxide, then let the mixture sit on the stain for an hour. For the worst kinds of stains, add baking soda and scrub.