Allergies or other respiratory ailments naturally cause mucus in the respiratory passages. Sometimes coughing or sneezing occurs suddenly, and there isn't time to grab a tissue to spare nearby items from the spray. This kind of sneezing or coughing suddenly can lead to mucus on your clothing. This usually won't create a serious stain on a T-shirt, as long as you wash the shirt quickly and appropriately.
Place the T-shirt in a sink. Rinse it in lukewarm water and then spray the stained area with a pre-wash laundry spray that contains enzymes. These are often labelled as sprays for protein-based stains. The enzymes help break these stains down.
Allow the product to remain on the shirt for a few minutes. The package should indicate exactly how long you should leave it on--usually it's up to 15 minutes.
Place the white T-shirt in your washing machine. If you have other white cotton items to wash, like bathroom towels, you can wash them with the T-shirt.
Add detergent and a capful of laundry bleach. Wash the shirt in warm water. If the stain remains after washing, re-treat it with the enzyme product and then let it soak in warm water for at least half an hour before rewashing.