Greying occurs due to damaging of the fabric and more importantly by soil re-deposition in the wash. The soil which re-deposits mostly contains of environmental soils, like soot in the air, household dust, sebum from skin etc. Another important part consists of stains (removed) from clothing in the wash.
Carbon Black Liquid
Stain removal is an important aspect of the wash performance for consumers, next to for instance colour maintenance. But consumer awareness about the fabric caring aspects of a detergent is growing as well.
Prevention: The Original PT-1:
Resolving: The Pre-Pilled PT-2: