Method 5 – Use bluing products
Bluing laundry products like Mrs. Stewart’s Bluing Concentrate offset the yellow/gray color of your sheets, making them look whiter. You can safely whiten sheets with bluing liquids made specifically for laundry.
*Please note that bluing is not a stain remover. It will only whiten whites, but you must spot-treat stains with other methods above. And never use too much bluing liquid, as it can turn your sheets blue. Always super-dilute it before use.
If you have a front loader washing machine, soak your yellow sheets with a few drops of blue in a tub filled with water. Soak for a few hours and then launder as usual. If you have a top load machine, wait until the machine is filled with water before adding the diluted blue into the detergent dispenser cup.