In their natural state, many fabrics have an off-white or yellowish cast and are, therefore, often bleached to remove their natural color. Manufacturers often add optical brighteners which make fabrics appear whiter and brighter. Occasionally, these agents break down, causing the fabric to revert to its natural off-white or yellowish color.
Exposure to light can break down fluorescent brighteners, causing the areas not exposed to light to be unaffected. Thus, the front of a sweater laid out to dry in the sun may turn yellow while the back remains white. Once this happens, it usually can't be corrected.
Graying of whites is another story. Dingy-looking whites are most often caused by incomplete soil removal over an extended period of time despite repeated washing. This can be caused by any or all of the following:
- Too little detergent
- Overloading the washing machine
- Water temperature too low
- Sorting clothes incorrectly
To remove this soil buildup and restore whiteness, take the following steps with washable items:
- Use the hottest temperature of water acceptable for the fabric
- Add 1-2 cups water conditioner
- Add detergent
- Add clothes and run through a complete wash and rinse cycle