How do detergents keep loosened dirt from settling back onto fabric?

Detergents prevent loosened dirt from settling back onto fabric by suspending the soil in a protective colloid, a process sometimes enhanced by special additives.1

To remain clean, the detached oil droplets and dirt particles must stay in a stable, highly dispersed condition within the wash water. If they are not kept in this state, they tend to flocculate—coalescing into larger aggregates that can easily redeposit onto the surface. By maintaining the dirt in a finely dispersed, deflocculated state, detergents ensure that these particles are small enough to be carried away through the interstices of the fabric during the washing process.1