Rinse the stain with cold water as soon as possible
Mix equal parts white vinegar and water
Apply the mixture to the stain and let it sit for 15 to 30 minutes
Gently rub the fabric against itself or with a soft brush
Make a paste with baking soda and water
Apply the paste to the stain and let it sit for 30 minutes
Wash the shirt in the hottest water safe for the fabric
Use an enzyme-based laundry detergent
Add oxygen bleach to the wash if the fabric allows
Avoid using chlorine bleach on sweat stains with protein buildup
Air-dry the shirt and check that the stain is gone before using heat
Repeat the treatment if needed before drying
For old stains, soak the shirt in oxygen bleach solution before washing