How can I clean sweat stains from shirts?

I use amonia and pour in area of odor. Let it sit for a while and then wash. It gets urine smell out of materials also.

If normal washing with a booster like Borax doesn't get it out, you will want to use some type of enzymatic cleaner like Clorox Urine Remover for stains & odors.

Here are some clothing smell removal basics:

1. Fresh Air hang it to air out smoke, fumes, smells
2. Put some straight vodka in a spray bottle and spray the area. That's what we use on concert tour clothing, especially if it can't be washed.
3. Armpit or crotch smell? Try using a dryer sheet folded over the seam, you can leave that there indefinitely, between wears.
4. Fabreeze...

If it's white, try a bit of lemon juice in about a 1/4 cup of hydrogen peroxide with 1 to 2 drops of Dawn dish soap. Blot on, rub gently, rinse and repeat if needed.

Works great on pee stains too.