If you tend to sweat alot, you probably have had problems with sweat stains on clothing. Fortunately, there are other ways to remove these kinds of stains without having to go to the expense of a drycleaner.
Pour a small amount of vinegar onto the stains and then GENTLY scrub. If you scrub too hard you may damage the fabric. Then allow to sit 30 to 60 minutes then wash as usual. You may need to repeat for very yellow stains, or stains that have set for a while.
If you face this problem frequently, check your deodorant. Many of the clear deodorants seem to result in sweat stains being more yellow than usual.