Check the care label before treating the shirt
Rinse the stained area with cold water
Make a paste of baking soda and water, then apply it to the stain
Let the paste sit for 30 to 60 minutes
Gently rub the fabric together or use a soft brush
Wash the shirt with laundry detergent in the hottest water safe for the fabric
Add oxygen bleach to the wash if the fabric allows it
Soak the shirt in a mixture of warm water and oxygen bleach for several hours
Use white vinegar on underarm stains before washing
Apply hydrogen peroxide to the stain and let it sit briefly before washing
Repeat the treatment if the stain remains
Dry the shirt in sunlight if possible after the stain is removed
Avoid using a dryer until the stain is fully gone