Soil is to blame for most stain complaints, where sugary drinks are spilled on a rug. Drinks such as coffee, sodas and juices all contain sugars which leave a stick deposit. This deposit then attracts soil from foot traffic leaving behind an unsightly stained area.
Many detergents are also guilty of staining when not adequately rinsed with plain water leaving behind a sticky detergent stain. The secret to clean rugs is properly rinsing with ample amounts of plain water.