Sweat is the most common stain in our daily life, also easily left on silk sheets. But you can deal with it yourself using supplies from home easily.
First, lay your sweat-stained silk bed sheets on a work surface with sweat stain facing up. Then, mix equal parts ammonia and water in a bowl. Wet a clean sponge with the solution and dab at the sweat stain. Allow the ammonia solution to sit on the sweat stain for a couple of minutes to remove it and restore color. Rinse the site of the sweat stain with cool water. If tackle old sweat stain, use a mixture of 1 tbsp. white vinegar in 1/2 cup cool water. Sponge the diluted vinegar on the sweat stain to remove the alkaline. Doing this will remove the discoloration and any remaining sweat stain and odor.
If you leave sweat stain on your pure silk sheets for a long time, those stains can also cause discoloration. So the faster, the better.