Thank you for letting us know your need.  Here is Dr. Laundry's recommendation in getting rid of yellow underarm stain. 

Underarm stains are a big problem to treat because they are highly variable.  Each person’s unique body chemistry combined with his/her choice of deodorant creates pretty individualized stains, and what works to remove one person’s stains doesn’t always work for another!  If you are trying to remove a crusty yellow build up of deodorant/antiperspirant mixed with body soil from a t-shirt, ideally you can avoid having it happen in the first place by pre-treating the armpits on the shirts before washing on a regular basis before stains develop.  Two effective pre-treating methods to try are:

1.  Pre-treat with Clorox® Bleach Pen Gel: use the broad scrubber tip to apply the gel and gently rub it into the armpit area.  Wash immediately in hot water with detergent and ¾ cup Clorox® Regular-Bleach.

2.  Pre-treat with a good liquid laundry detergent that contains an enzyme.  Wait 5-10 minutes, but don’t let it dry on the fabric.  Wash in hot water with detergent + Clorox2® Stain Fighter and Color Booster.

Unless you have an obvious stain you were trying to remove, you can tumble dry t-shirts with the rest of your white load. 

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