Sheets yellow over time because of the build-up of dead skin cells, sweat, and body oils. Washing your sheets frequently and showering before bed can help reduce the amount of oil and dirt in your sheets and delay yellowing. In addition, you can do other things like: Avoid eating in bed to keep spills from staining your sheets. Launder your white sheets separate from colors. Remove makeup before bed. Don’t use fabric softeners (they can deposit color).