Those yellow mystery stains on your polyester shirt or tennis skirt might be perspiration, iron stains or even food stains. To treat them, start with basic stain removing techniques, or use a commercial rust remover if you suspect the stain is rust. Don't expose polyester to high heat. Polyester is a durable, stain-resistant fabric, but it melts or becomes permanently wrinkled when exposed to high temperatures.
Dab the stain with stain remover stick. Pour 1/4 cup heavy-duty liquid detergent directly on the stain. Rub the fabric so the detergent is thoroughly distributed throughout the stain.
Wait 30 minutes and wash in a gentle wash cycle on cold. Examine the garment. If the stain remains, reapply detergent and soak the garment overnight in cold water. Rinse and wash the garment.
Dry the garment on low and remove it when it is damp dry. Polyester wrinkles easily in a hot dryer. Do not dry the garment until the stain is completely removed. Doing so will set it permanently.