Proteins found in perspiration cause yellow armpit stains. To get rid of the stains, you must eliminate the proteins that contain urea, the same chemical that causes urine to be yellow. Follow a multi-step approach to achieve the best result, but avoid putting the shirt in a dryer until you know the stains are gone.Continue Reading
When you know a shirt has perspiration stains, pretreat them using your normal liquid laundry detergent. Measure the amount required for a normal load. Pour a little from the cup onto the stain and rub it into the fabric. Once all the shirts are treated, pour the remaining detergent into the washing machine. Fill with the hottest water appropriate for the garments and wash as normal. Check for stains.
Ammonia, while smelly, helps to remove stubborn stains from the armpits of the shirt. Use ammonia in a well-ventilated area to scrub the stains and then launder as normal. Ammonia is also effective at removing the underarm residue from dark shirts that make them stiff, even though the stain isn't apparent.
Prevent yellow stains by using a deodorant that doesn't contain aluminum. While aluminum-containing antiperspirants reduce sweat, they increase staining. Protect your dress shirts by wearing an undershirt.