Why does detergent lower the surface tension of water?

Detergents lower the surface tension of water by acting as surface-active agents, or surfactants. Water molecules naturally have a strong affinity for one another, which creates surface tension. Detergents disrupt this by reducing that affinity, thereby increasing the liquid's ability to spread and wet surfaces.12

This occurs because detergent molecules possess a unique chemical structure consisting of two distinct parts:
* A hydrophobic (water-insoluble) part: Typically a long-chain carbon group or fatty acid that attaches to soil or oily surfaces.1
* A hydrophilic (water-soluble) part: Such as a sulfo or ethylene oxide group, which attaches to the water.1

By concentrating at the interfaces between water and other materials, these molecules effectively break the cohesive forces between water molecules. This process facilitates the wetting of surfaces and the penetration of fibers, which is the essential first step in the cleaning process.12