Sweat stains are a fact of life, especially on certain areas of your clothing such as the armpit. The process for getting sweat stains off polyester fabric often depends upon the garment. Always refer to care instructions before proceeding with spot cleaning and try a spot test to ensure the garment doesn't become damaged. In addition, never use bleach to clean sweat stains because the chlorine reacts with the proteins in sweat and will make the satin darker.
Apply full-strength liquid laundry detergent directly to the perspiration stain.
Allow the detergent to sit on the stain for about 30 minutes. Launder your polyester garment as normal and allow it to air dry, as machine drying will set the stain in if it has not lifted yet.
Mix a vinegar and water stain remover if the polyester still has a sweat stain. Use 1/2 cup water and 1 tbsp. white vinegar. Apply it directly to the stain.
Wait about 30 minutes with the vinegar mixture soaking on the stain. Launder the stained polyester in cold water. Air dry and check to see if the stain is gone.