If you notice yellowish-brown discoloration on your white clothing, sweat and/or deodorant are likely culprits. There is no need to throw out a white shirt that is in otherwise good condition just because of these stains. A variety of common household products will treat deodorant and sweat stains on white clothing.
Removing Sweat Stains
Fill a bowl with 1/2 cup lukewarm water. Add 1/2 cup household ammonia to the bowl and stir with a spoon.
Dip a rag into the bowl and wring it out lightly. Dab a generous amount of the solution onto the sweat stain.
Allow the mixture to remain on the clothing for a few minutes. Launder the garment as usual.
Use aspirin if the stain persists after washing. Fill a bowl with 1/2 cup lukewarm water. Add two aspirins to the bowl. Wait a few minutes until the aspirin completely dissolves into the water.
Pour the mixture onto the perspiration stain. Allow the mixture to remain on the garment for 2 hours.
Pour a few drops of clear liquid laundry detergent onto the stained area of the garment. Rub the fabric with your fingers. Launder the item as usual.
Removing Deodorant Stains
Fill a bucket with equal parts white vinegar and warm water. Place the garment into the bucket.
Swish the garment around in the bucket a few times with your hands. Make sure that the deodorant stained portion of the garment is completely submerged in the water.
Allow the garment to sit in the bucket for at least 2 hours. If possible, leave it in the bucket overnight.
Apply a laundry pretreatment spray, such as Shout or Spray 'n Wash, to the deodorant stain. Let it sit for a few minutes before laundering as usual.
Use salt water if the stain persists. Fill a bowl with 1 qt. hot water. Add 1/2 cup salt and stir until the salt has completely dissolved.
Dip a white rag into the bowl. Sponge the salt water solution on the stain. Add more salt water and continue sponging until the stain has lifted. Launder the garment as usual.
Use baking soda and water for an alternate method for removing sweat stains. Mix 4 tbsp. baking soda with 1/4 cup warm water. Stir to form a paste. Rub the paste into the stain, let it sit for 2 hours and launder as usual.
Never mix bleach and ammonia, or products containing these ingredients. The results could be toxic.