One of the easiest ways to soften sheets is with white vinegar. While laundry detergent can help soften scratchy sheets, certain detergents can actually have the opposite effect and make the sheets too stiff.
The most-effective way to soften sheets is by adding 2 cups of white vinegar to the washing machine when washing sheets. Using vinegar to wash sheets also eliminates the need to use fabric softeners or dryer sheets. Another way to soften scratchy sheets is by using baking soda instead of laundry detergent. SF Gate recommends using a cup of baking soda in place of detergent and then adding a cup of white vinegar to the washing machine during the rinse cycle.